- Email: [email protected]
Enhanced relative cooling power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties
Accepted Manuscript Enhanced Relative Cooling Power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties R. Ben Hassine, W. Cherif, J.A. Alonso, F. Mompean, M.T. Fernández-Díaz, F. Elhalouani PII:
S0925-8388(15)30431-X
DOI:
10.1016/j.jallcom.2015.07.034
Reference:
JALCOM 34723
To appear in:
Journal of Alloys and Compounds
Received Date: 21 April 2015 Revised Date:
29 June 2015
Accepted Date: 3 July 2015
Please cite this article as: R. Ben Hassine, W. Cherif, J.A. Alonso, F. Mompean, M.T. FernándezDíaz, F. Elhalouani, Enhanced Relative Cooling Power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.07.034. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Graphical abstract
Enhanced Relative Cooling Power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties. J.A. Alonso, F. Mompean M.T. Fernández-Díaz, F.
RI PT
R. Ben Hassine, W. Cherif,
EP
TE D
M AN U
SC
Elhalouani
AC C
The title perovskites present a crystallographic phase transition from an orthorhombic structure (Pnma) for x=0 to a rhombohedral structure (R-3c) for Fe-doped samples, as shown in a neutron study. Magnetic data show that x = 0 and x = 0.1 perovskites exhibit sharp paramagnetic-ferromagnetic transitions. The relative cooling power (RCP) is as high as 241 J.Kg-1 for x= 0.1, being a promising candidate for magnetic refrigeration.
ACCEPTED MANUSCRIPT
Enhanced Relative Cooling Power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties. R. Ben Hassine,a W. Cherif,
a
J.A. Alonso,b* F. Mompean,b M.T. Fernández-Díaz,c F.
RI PT
Elhalouani d a
Sfax University, Faculty of Sciences, B. P. 1171 - 3000, Tunisia.
b
Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones
Científicas, Cantoblanco, E-28049 Madrid, Spain. d
SC
Institut Laue-Langevin, B.P. 156, F-38042 Grenoble Cedex 9, France
Sfax University, National School of Engineers, B. P. W 3038, Tunisia.
M AN U
c
Abstract:
We present the structural and magnetic properties of a novel series of La0.67Sr0.22Ba0.11Mn1-xFexO3 (0≤x≤0.3) perovskites prepared by the sol-gel method. These oxides were characterized by x-ray (XRD), neutron powder diffraction (NDP) at room
TE D
temperature and magnetization measurements versus temperature and various applied magnetic fields. The NPD data, very sensitive to the octahedral tilting, show a crystallographic phase transition from an orthorhombic structure (Pnma) for x=0 to a rhombohedral structure (R-3c) for Fe-doped samples. Magnetic data show that x = 0 and x =
EP
0.1 perovskites exhibit a paramagnetic-ferromagnetic transition at low temperature, while for 0.2≤x≤0.3 a strong divergence between ZFC and FC curves suggest the presence of
AC C
antagonistic antiferromagnetic and ferromagnetic interactions. The magnetic entropy change (│∆Smax│) takes values of 2.46 J Kg-1 K-1, 2.43 J Kg-1 K-1 and 0.91 J Kg-1 for x = 0, x = 0.1 and 0.2 , respectively at 5 T . The relative cooling power (RCP) amounts 169 J.Kg-1, 241 J.Kg-1 and 70 J.Kg-1 at 5 T for x= 0, 0.1, 0.2 respectively. These values are compared favorably
with
those
of
some
others
reported
manganites,
making
La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 a promising candidate for magnetic refrigeration. Keywords: Sol gel, X-Ray diffraction, Neutron diffraction, Curie temperature, Magneto caloric effect
ACCEPTED MANUSCRIPT *Corresponding autor. Email : [email protected]
1-Introduction:
perovskite
ABO3-type
manganites
with
the
general
formula
RI PT
Recently,
,where Ln is a rare earth (Ln = La, Pr…) and A is a divalent alkali-earth element (A= Ca, Sr, Ba……), have been the subject matter of a large number of studies due to their interesting structural and magnetic properties [1]. These perovskites are
SC
simultaneously metallic and ferromagnetic below Curie temperatures close to room temperature, by virtue of a well-known double-exchange effect.
M AN U
Given their ferromagnetic properties, many works on the magnetocaloric effect (MCE) involving perovskite-type rare-earth manganites have attracted considerable attention of the scientific community over the past years, due to their potential applications [2-3], such as magnetic refrigeration (MR). Comparing with the gas compression refrigeration, this technology exhibits significant advantages such as high efficiency and minimal environmental
TE D
impact [4,5]. The magnetocaloric effect (MCE) is characterized by the isothermal change of the magnetic entropy and the adiabatic change of temperature, induced by the application of an external magnetic field [5]. The main requirements for a magnetic material to possess a large │∆SM│, are a large spontaneous magnetization as well as a sharp drop in the
EP
magnetization associated with the ferromagnetic to paramagnetic transition at the Curie temperature TC [6,7].
AC C
The MCE property is usually explained by the double exchange interaction (DE)
between the trivalent (Mn3+) and tetravalent (Mn4+) ions [8] contained in mixed-valence manganites. To enhance this property many studies have discussed the effect of Fe doping on the structural and magnetic properties. Such manganites have a complex band structure containing trivalent Mn3+ and trivalent Fe3+ ions occupying both octahedral (B) sites [9,10]. The substitution of Mn ions by Fe ions in AMn1-xFexO3 manganites, introduces lattice distortions but also reduces the Mn3+/Mn4+ ratio.
In this work, we present the effect of the substitution of the Mn ions by Fe ions on the structural and magnetic properties of La0.67Sr0.22Ba0.11Mn1-xFexO3 (0 ≤ x ≤ 0.3) compounds
ACCEPTED MANUSCRIPT and the magnetocaloric effect for the La0.67Sr0.22Ba0.11MnO3 , La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 and La0.67Sr0.22Ba0.11Mn0.8Fe0.2O3 samples. In this perovskite series we have optimized TC by doping with 33% of alkali-earth cations at the A positions of the perovskite, and we have increased the tolerance factor by partially replacing Sr by Ba: the larger ionic radius of Ba2+ ions leads to an increase of the perovskite symmetry, opening of the superexchange Mn-O-
RI PT
Mn angles between octahedral units, thus favouring double exchange, enhancing the ferromagnetic interactions and hence the Curie temperature. The structural analysis from NPD data show interesting features, neutrons being sensitive to the oxygen positions and thus allowing determining the tilting systems and Mn-O distances and Mn-O-Mn angles with
upon Fe doping the Mn position of the perovskites.
M AN U
2-Experimental
SC
precision; these data have been essential to correctly characterize a phase transition observed
Samples with nominal composition La0.67Sr0.22Ba0.11Mn1-xFexO3 (x= 0, 0.1, 0.2, 0.3) were synthesized by the sol–gel method from MnCO3, La2O3, SrCO3, BaCO3 and Fe2O3 (99.9% purity) in the appropriate stoichiometric proportions. The powders were dissolved in
TE D
nitric acid, HNO3. Suitable amounts of citric acid and ethylene glycol as a chelating agent were added until a completely homogeneous and transparent solution was achieved. At this stage, the PH is considerably acid, around 1.2. During the subsequent gentle heating leading to the evaporation of the solvent and partial elimination of HNO3 as NO2 vapors the PH
EP
increases until 1.5, when the resin is formed. After slowly drying the solution, it was decomposed at 600ºC in air. Finally, the resulting powders were annealed in air at 1000 °C.
AC C
The structure, phase purity and homogeneity of the as-elaborated samples were checked by Xray powder diffraction (XRD) using CuKα radiation (λ = 1.54056 Å) and neutron powder diffraction (NPD). The crystallographic structures were refined from high resolution NPD patterns collected at the Institut Laue-Langevin (ILL) in Grenoble (France), acquired at room temperature at the D2B diffractometer with λ=1.594(1) Å. About 3 grams of each sample were contained in vanadium cylinders; the counting time was 2 hours for each data collection in the high-intensity mode. The diffraction data were analyzed by the Rietveld method using the FULLPROF program [11] and the average particle size was determined using the Scherrer formula implemented in this software. A pseudo-Voigt function was chosen to generate the line shape of the diffraction peaks. The background was approximated with a 5th-degree polynomial.
ACCEPTED MANUSCRIPT The following parameters were refined in the final runs: scale factor, background coefficients, zero-point error, pseudo-Voigt corrected for asymmetry parameters, positional coordinates, isotropic displacement factors and mixed occupancy factors of Mn/Fe. The coherent scattering lengths for La, Sr, Ba, Mn, Fe, and O were 8.240, 7.02, 5.07, -3.438, 9.45 and 5.805 fm,
RI PT
respectively.
Magnetic measurements were performed on a commercial SQUID magnetometer from Quantum Design; the dc magnetic susceptibility was recorded in the temperature range 5-450 K in ZFC and FC runs with an applied field of 0.1 T with a heating rate of 5 K min-1;
SC
magnetization isotherms were collected between –50 kOe and +50 kOe with ∆T= 8K between 300 to 420 K (x= 0) and 180 to 260 K (x= 0.1). The magnetic entropy changes |∆SM| were
3-Results and discussion 3.1 Crystallographic structure
M AN U
estimated from the magnetization data using a Maxwell relation.
TE D
Fig. 1 shows the XRD patterns of the four compounds described in this work. They show reflections characteristic of pure perovskite phases. They have been Rietveld-refined with the structural models derived from NPD data, described immediately below. No impurity phases
EP
are observed in any of the diagrams. From XRD data it is difficult to determine any deviation from the cubic symmetry, since the structural distortion is weak and the superstructure
AC C
reflection are almost invisible, hence NPD are required. The NDP analysis for La0.67Sr0.22Ba0.11Mn1-xFexO3 (0≤x≤0.3) helped to assess the true symmetry and structural features of these oxides. For x= 0 the pattern can be refined in the standard orthorhombic (Pnma) space group, whereas for x ≥ 0.1 a symmetry change is observed, and the crystal structures need to de defined in the rhombohedral R-3c space group A structural transition is thus identified as Fe is introduced into the crystal structure. Similar results were observed by Tlilia and al. in ref [12] in the La0.75Ca0.08Sr0.17 Mn1-xFexO3 series. The crystal structure of La0.67Sr0.22Ba0.11MnO3 was indexed in an orthorhombic unit cell with unit-cell parameters related to a0 (ideal cubic perovskite, a0≈ 3.8 Å) as a≈c≈√2a0; b≈ 2a0, in
ACCEPTED MANUSCRIPT the Pnma space group. In this model La, Sr and Ba are distributed at random over the 4c (x,1/4,z) positions, Mn atoms occupy a single position at 4b (0,0,1/2) Wyckoff sites, and there are two independent positions for oxygens, O1 (4c) and O2 (8d). The lattice parameter values obtained in the fitting are presented in Table 1, as well as the atomic positions; some selected interatomic distances (Mn-O bond distances) and Mn-O-Mn bond angles are listed in
RI PT
Table 2. The good agreement between experimental and calculated XRD and NDP profiles after the Rietveld refinements are displayed in Figs. 1a and 2a, respectively. No extra peaks were detected in the XRD or NPD patterns that could indicate the presence of impurities in the sample.
SC
For x ≥ 0.1 a phase transition to a rhombohedral R-3c symmetry is observed; in this structure La, Ba and Sr are randomly distributed at 6a (0,0,1/4) sites, Mn and Fe statistically distributed
M AN U
over the 6b (0,0,0) positions and a single type of oxygen atoms O1 at 18e (x,0,1/4). The unit cell and atomic parameters, as well as discrepancy factors after the refinement from NPD data, and main interatomic distances and angles are gathered at Table 1. The goodness of the fit for the three compounds with x= 0.1, 0.2 and 0.3 are displayed at Figs. 1b-d for XRD data
TE D
and Figs. 2b-d for NPD data, respectively. No impurities appear at any XRD of NPD pattern.
Fig. 3 and Fig. 4 display two views of the orthorhombic (x= 0) and rhombohedral (x = 0.1) structures, highlighting the occurrence of deformed octahedra for the orthorhombic perovskite, allowing for the manifestation of a Jahn-Teller distorsion corresponding to the
EP
presence of 67% of Mn3+ ions (as derived from the nominal doping), whereas for the rhombohedral phase this distortion is not allowed for the symmetry of the space group, the
AC C
octahedra containing six equivalent Mn-O distances, as observed in a previous work [13].
Fig. 5a exhibits the variation of unit-cell volume for a single perovskite unit (taking into account that Z= 4 and 6 for the Pnma and R-3c space groups, respectively), bond distances and Fig. 5b the bond angles as a function of iron contents. From x= 0 to x= 0.1 there is a considerable increase of the unit-cell volume, which is softened for higher Fe contents, once the rhombohedral symmetry is established. This is not easily deduced from the similarity in ionic radii between Fe3+ and Mn3+, of 0.645 Å in six-fold coordination and high-spin state for both cations [14]. We can speculate that the introduction of Fe3+ decreases the effectiveness of the hole doping effect given by the replacement of 33% La by alkali-earth ions, leading to a lower content of Mn4+ at the Fe-doped samples, showing a higher unit-cell
ACCEPTED MANUSCRIPT volume and distances. On the other hand, a conspicuous increase of the unit-cell volume has also been observed in other series of compounds where Mn3+ is replaced by Fe3+; for instance in ErMnFeO5 an expansion by 1% in the volume is reported [15] with respect to ErMn2O5. In the present case the reduction of the average octahedral size also accounts for an increase of the perovskite geometric tolerance factor t ≡ (A-O)/[√2(B-O)] and
RI PT
the concomitant increase of symmetry upon Fe introduction into the lattice, driving a structural phase transition from an orthorhombic to rhombohedral symmetry.
Whereas the Pnma space group involves a-b+c- tilting of the octahedra (in antiphase along the
SC
a and c directions of the aristoptype, and in phase along the long b-axis direction), the R-3c space group allows cooperative octahedral-site tilting along the [111] direction of the primary unit cell or the c axis in the hexagonal cell. A few perovskite oxides A3+B3+O3 with t ≤ 1
M AN U
adopt the R-3c crystal structure at ambient pressure, i.e. RAlO3 (R= La, Pr, Nd), LaCoO3, LaNiO3, LaCuO3, LaGaO3 (at T > 540 K). The rhombohedral phase can also be stabilized under pressure: the X-ray powder diffraction of LaMnO3 under 12 GPa can be refined well with the R-3c structure [16]. In the present case we have seen that subtly modifying the B octahedral sublattice with suitably chosen elements also drives the mentioned increased in
TE D
perovskite symmetry. In the present case this has the advantage of increasing the superexchange Mn-O-Mn angles (Fig. 5b), improving the overlap between Mn 3d and O 2p orbitals and thus enhancing the magnetic interactions, which are the properties of interest of
EP
the present materials.
It is interesting to compare the present compounds with La0.67Ba0.22Sr0.11Mn1-xFexO3 (x = 0,
AC C
0.1, 0.2, 0.3 and 1.0) described in Ref. [17]. In this system the samples with x≤ 0.3 are described as orthorhombic from XRD data, contrasting with the present perovskites, where NPD data, very sensitive to the octahedral tilting, unveil a crystallographic phase transition from an orthorhombic structure (Pnma) for x=0 to a rhombohedral structure (R-3c) for Fedoped samples. Comparing the undoped x=0 compounds we observe that the size of the unit cell decreased from V/Z*=59.17 Å3 for La0.67Sr0.11Ba0.22MnO3 [17] to 58.21 Å3 for the present La0.67Sr0.22Ba0.11MnO3 perovskite, which is expected from the larger ionic size of Ba2+ vs Sr2+. In our case we could detect from the neutron study that the samples experienced a transition to a rhombohedral symmetry for Fe-doped compounds; the higher tolerance factor for the Ba0.22 series [17] would have led to a similar transition; however from the XRD patterns the
ACCEPTED MANUSCRIPT authors could not detect such a subtle feature, which is not surprising given the fair crystallinity of their samples.
We employed the Scanning Electron Microscopy (SEM) in order to examine the morphology
RI PT
of the La0.67Sr0.22Ba0.11Mn1-xFexO3 samples (x = 0, 0.1, 0.2, 0.3 and 1.0). SEM images reveals the presence of some pores in the samples, probably related to the preparation procedure from citrate precursors, and a good connectivity between the grains.
M AN U
SC
The average crystallite size was estimated from the NDP data using the Scherrer relation [18]:
Here K, ᵝ, λ, and Ѳ are the grain shape factor, the X-ray wavelength, the full width at half maximum (FWHM) of the diffraction peak, and the Bragg diffraction angle, respectively. The values of the effective crystallite sizes are summarized in Table 1. In all cases a nanometric size for the crystallites is found, around 30 nm, which is related to the moderate synthesis
procedures.
EP
3.2 Magnetic properties
TE D
temperatures of these samples, of 1000ºC, obtained from very reactive precursors from sol-gel
The ZFC and FC M(T) curves are presented in Fig. 7. Fig. 7a shows the thermal
AC C
variation of the susceptibility for x=0 and 0.1 samples; both exhibit a ferromagnetic (FM) to paramagnetic (PM) phase transition as the temperature increased. The Curie temperature TC, can be determined by the minimum of dM/dT at the inflection point of the FC M(T) curve. The Curie temperature decreased with doping iron from 360 K to 232 K for La0.67Sr0.22Ba0.11MnO3 and La0.67Sr0.22Ba0.11Fe0.1Mn0.9O3, respectively. Interestingly, the TC for x= 0 is well above RT, as expected for the high tolerance factor of this perovskite, containing both Sr and Ba ions at the A sublattice; this ferromagnetic behavior is due to the double exchange effect associated with the mixed Mn valence at the octahedral sublattice (nominally 66% Mn3+ 33% Mn4+). The introduction of Fe very fast perturbs the double exchange leading to a decrease of the Curie temperature, since the presence of Fe3+ establishes antiferromagnetic interactions in the octahedral sublattice. Yet, in our samples the
ACCEPTED MANUSCRIPT decrease of TC per 1% Fe doping is approximately 13 K, smaller from that obtained for the Nd0.67Sr0.33Mn1-xFexO3 system [19,20], where a drop of 18 K per 1% Fe was observed. The M(T) curves for the samples x=0.2 and x=0.3 show that the magnetization progressively decreases (Fig. 7b). At a temperature Tm, indicated by arrow in Fig. 7b, a bifurcation between
RI PT
the FC and ZFC curves (λ shape) is observed ,which is generally associated in the literature of manganites with the appearance of antiferromagnetic interactions antagonistic with the ferromagnetic double-exchange interactions. These interactions sometimes give rise to a glass magnetic state, with a spin- or cluster-like freezing process [21,22]. However, this could also
SC
be a result of the magnetic anisotropy and other authors consider that the competition between the ferromagnetic DE interactions and the coexisting anti-ferromagnetic super exchange interactions with the introduction of Fe3+ for Mn3+ could drive the system supposedly into a
M AN U
random canted ferromagnetic state at low temperatures [23].
In comparison with the magnetic properties of the La0.67Sr0.11Ba0.22Mn1-xFexO3 series [17], we found that the Curie temperature for La0.67Sr0.22Ba0.11MnO3 (360 K) is higher than that of La0.67Sr0.11Ba0.22MnO3 (TC= 345 K [17]); the shorter Mn-O distances observed in the former
TE D
perovskite account for the enhanced FM interactions found in the present perovskite oxide. As observed in the present series, an even sharper decrease of the Curie temperature upon Fe doping is reported in Ref [17], also explained by the appearance of AFM Fe-O-Fe and Fe-OMn superexchange interactions competing with the FM double exchange; for instance, for x=
AC C
K.
EP
0.1, TC= 190 K [17] in contrast with the present La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 with TC= 268
3.3 Magnetic caloric effect
Fig. 8(a-b) show isothermal magnetization curves for La0.67Sr0.22Ba0.11MnO3 and
La0.67Sr0.22Ba0.11Fe0.1Mn0.9O3 samples (hereafter called LSBMO and LSBMFO, respectively), measured under applied magnetic fields ranging between 0-5 T and at temperatures spanning from 300 to 420 K and 180 to 300 K, respectively. The isothermal magnetization M (H, T) magnetic field dependency, measured at different temperatures below TC, shows a non-linear behavior with a sharp increase for low field values and a tendency to saturation as the
ACCEPTED MANUSCRIPT magnetic field increases, reflecting a ferromagnetic behavior. Beyond the Curie temperature, the material follows a paramagnetic behavior in which the ferromagnetic order is broken, due to the random reorientation of the magnetic moments for to thermal agitation [24]. In Fig. 9a and 9b displays the Arrott curves (µ 0H/M vs M2) for LSBMO and
RI PT
LSBMFO deduced from isothermal magnetization curves recorded around TC for both samples in a magnetic field up to 5 T. According to Banerjee’s criterion [25], a negative or positive sign of the slope of Arrott curves corresponds to a first-order or second-order magnetic phase transition, respectively. The results obtained from µ 0H/M versus M2 plots of
SC
LSBMO and LSBMFO show a positive slope in all cases in the complete M2 range, confirming that a second-order FM to PM phase transition has occurred.
M AN U
The temperature dependence of│∆SM│ has been determined from the M (H) isotherms. Figure 10a and b show the magnetic entropy change │∆SM│ for both samples as a function of temperature under different magnetic fields: 1,2,3,4 and 5T. From the M (H, T) data, the magnetic entropy change for our samples can be calculated as [26]:
TE D
(1)
In the case of magnetization measurements at small discrete field and temperature intervals,
EP
numerical approximation of the integral in Eq. (1) could be approximated as [27]:
AC C
(2)
where Mi and Mi+1 are the experimental data of the magnetization Ti and Ti+1, under a magnetic field Hi.
In Fig. 8a, b and c we observe that |∆SM| increases with an increasing applied magnetic field, the maximum entropy change corresponding to a magnetic field variation of 1, 2, 3, 4 and 5 T for
La0.67Sr0.22Ba0.11MnO3
is
0.35;
0.98;
1.49;
1.97;
2.46
JKg-1K-1,
for
La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 it is 0.48; 1.02; 1.42; 1.82; 2.43 JKg-1K-1 and for La0.67Sr0.22Ba0.11Mn0.8Fe0.2O3 it is 0.09; 0.28; 0.48; 0.68; 0.91 JKg-1K-1, respectively.
ACCEPTED MANUSCRIPT The magnetic cooling efficiency of a magnetocaloric material is evaluated by considering the relative cooling power (RCP) [28] given by:
RI PT
where │∆Smax│ is the maximum entropy change at TC and is equal to δTFWHM = (T2-T1), the full-width temperature span of the |∆SM| versus temperature plots at their half-maxima. The results of this estimation are show in Fig 11. The Rcp values exhibit a linear increase with increasing field for all compounds. For our samples, the Rcp values are 169 J.Kg-1, 241
SC
J.Kg-1 and 70 J.Kg-1 at 5 T for x= 0, 0.1, 0.2 respectively.
In Table 3 the present results are compared with those of similar systems (perovskite
M AN U
manganites) taken from the literature, achieving weaker responses than those described here. The Rcp of La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 compound is higher than those obtained by F. Ben Jemaa et al [17] for La0.67Sr0.11Ba0.22Mn0.9Fe0.1O3 prepared by sol-gel method, superior than La0.67Sr0.22Ba0.11MnO3 oxide reported by D.T. Morelli et al [30] and, in general, better than all perovskite oxides, only overcome by Gd metal [31]. The replacement of Mn by Fe ions is
TE D
certainly advantageous, as shown in Table 3, with respect to Mn-only containing compounds. The values of Rcp are extended over a wide range of temperature around the Curie temperatures and hence these materials are useful for near-room-temperature magnetic
AC C
4. Conclusion
EP
refrigeration applications.
La0.67Sr0.22Ba0.11Mn1-xFexO3 compounds were prepared by sol–gel method and
sintered at 1000 °C, yielding nanometric powders. NPD data show that these perovskites crystallize, for x= 0, in an orthorhombic structure (Pnma space group) and undergo a transition to a rhombohedral superstructure of perovskite (R-3c) for Fe contents x≥ 0.1. This is due to the increment of the average <(Mn,Fe)-O> distances in the octahedral positions, leading to a concomitant increase of the tolerance factor of the perovskite. Magnetic measurements show a ferromagnetic behavior for x=0 (TC= 360 K) and 0.1 (TC= 232 K) samples, whereas compounds with x≥0.2 present a divergence of FC and ZFC curves due to the appearance of antagonistic antiferromagnetic interactions upon introduction of Fe3+
ACCEPTED MANUSCRIPT moments, that compete with the double exchange effect associated with the mixed Mn3+,4+ valence. The relative cooling power Rcp is 168 (J Kg-1) and 241 (J Kg-1) for the samples x=0 and x=0.1 under ∆H= 5T respectively. Hence, the compound doped by Fe (x=0.1) is a candidate for magnetic refrigerant, performing better than most related perovskites.
RI PT
Acknowledgements
We acknowledge the financial support of the Spanish Ministry of Economy and Competitivity
AC C
EP
TE D
M AN U
SC
the project MAT2013-41099-R. We are grateful to ILL for making all facilities available.
ACCEPTED MANUSCRIPT References [1]
R. Von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer, Phys. Rev. Lett. 71 (1993) 2331.
[2]
S. Othmani, R. Blel, M. Bejar, M. Sajieddine, E. Dhahri, E.K. Hlil, Solid State
RI PT
Commun. 149 (2009) 969. [3]
L. Li, K. Nishimura, M. Fujii, K. Mori, Solid State Commun. 144 (2007) 10.
[4]
O. Tegus, E. Bruck, K.H.J. Buschow, F.R. de Boer, Transition-metal- based magnetic refrigerants for room-temperature applications, Nature 415 (2002) 150–152.
A.M. Tishin, I. Spichkin, The Magnetocaloric Effect and its Applications, Institute of Physics Publishing, Bristol, 2003.
S.Y. Dan’kov, A.M. Tishin, V.K. Pecharsky, K.A. Gschneidner, Phys. Rev. B57
M AN U
[6]
SC
[5]
(1998) 3478. [7]
M.H. Phan, S.C. Yu, N.H. Hur, Appl. Phys. Lett. 86 (2005) 072504.
[8]
C. Zener, Interaction between the d shells in the transition metals, Phys. Rev. 81(1951)440–444.
[9]
G.H. Rao, J.R. Sun, A. Kattwinkel, L. Haupt, K. Baerner, E. Schmitt, E. Gmelin,
[10]
TE D
Physica B 269 (1999) 379.
M. Sugantha, R.S. Singh, A. Guha, A.K. Raychaudhuri, C.N.R. Rao, Mater. Res. Bull. 33 (1998) 1129.
J. Rodríguez-Carvajal, Physica B (Amsterdan) 192 (1993) p. 55.
[12]
M.T. Tlili, M. Bejar, E. Dhahri, M. Sajieddine, M.A. Valente, E.K. Hlil, Materials
EP
[11]
Characterization. 62 (2011) 243-247. M. Ellouze, W. Boujelben, A. Cheikhrouhou, H. Fuess, R. Madar, Solid State
AC C
[13]
Commun. 124 (2002) 125.
[14] [15]
R.D. Shannon, Acta Cryst. A, 32, (1976) 751.
A. Muñoz, J. A. Alonso, M. J. Martínez-Lope, and J. L. Martínez, Phys. Rev. B 72, 184402 (2005).
[17]
F. Ben Jemaa, S. Mahmood , M. Ellouze , E.K. Hlil, F. Halouani , I. Bsoul , M. Awawdeh, J. Solid State Sci. 37 (2014) 121-130.
[18]
A. Guinier, in: X. Dunod (Ed.), Theorie et Technique de la Radiocristallographie, p. 482. third ed., 1964
[19]
J. Takeuchi, S. Hirahara, T.P. Dhakal, K. Miyoshi, K. Fujiwara, Colossal
ACCEPTED MANUSCRIPT magnetoresistance of perovskite Nd0.67Sr0.33Mn1-xFexO3 single crystals, J. Magn. Magn. Mater. 226–230 (2001) 884–885. [20]
Y.L. Chang, Q. Huang, K. Ong, Effect of Fe doping on the magnetotransport properties in manganese oxides, J. Appl. Phys. 91 (2002) 789–793.
[21]
J.A. Mydosh, Spin-Glass: An experimental Introduction, Taylor& Francis, London,
[22]
RI PT
1993. M. Baazaoui, S. Zemni, M. Boudard, H. Rahmouni, A. Gasmi, A. Selmi, M. Oumezzine, Magnetic and electrical behaviour of La0.67Ba0.33Mn1-xFexO3 perovskites,
[23]
SC
Mater. Lett. 63 (2009) 2167–2170.
D. C. Kundaliy, R. Vij, R.G. Kulkarni, A.A. Tulapurkar, R. Pinto, S.K. Malik, W.B. Yelon,
Structural,
magnetic
and
magnetotransport
properties
of
the
Materials, 264, 2003, 62–69.
[24]
M AN U
La0.67Ca0.33Mn0.9Fe0.1O3 perovskite, Journal of Magnetism and Magnetic
B. Arayedh, S. Kallel, N. Kallel, O. Peña, Influence of non-magnetic and magnetic ions on the Magneto-Caloric properties of La0.7Sr0.3Mn0.9M0.1O3 doped in the Mn sites
TE D
by M= Cr, Sn, Ti, J. Magn. Magn. Mater. 361 (2014) 68–73. [25]
S.K. Banerjee, Phys. Lett. 12 (1964) 16.
[26]
X. Bohigas, J. Tejada, M.L. Martinez-Sarrión, S. Tripp, R. Black, Magnetic and calorimetric measurements on the magnetocaloric effect in La0.6Ca0.4MnO3, J. Magn.
[27]
EP
Magn. Mater. 208 (2000) 85–92.
R.D. McMichael, J.J. Ritter, R.D. Shull, Enhanced magnetocaloric effect in Gd3Ga5-xFexO12, J. Appl. Phys. 73 (1993) 6946–6948. M.H. Phan, S.C. Yu, Review of the magnetocaloric effect in manganite materials, J.
AC C
[28]
Magn. Magn. Mater. 308 (2007) 325–340.
[29]
D.T.Morelli, A.M.Mance, J.V.Mantese, A.L.Micheli, Magnetocaloric properties of doped lanthanum manganite films, J.Appl.Phys.79(1996) 373–375.
[29]
C.P. Reshmi, S.Savitha Pillai, K.G.Suresh, Manoj Raama Varma, Room temperature magnetocaloric properties of Ni substituted La0.67Sr0.33MnO3, Solid State Sci.19(2013)130–135.
[30]
Y.Sun, W.Tong, Y.H.Zhang, Large magnetic entropy change above 300 K in La0.67Sr0.33Mn0.9Cr0.1O3, J. Magn. Magn. Mater.232 (2001) 205–208.
ACCEPTED MANUSCRIPT V.K. Pecharsky Jr., K.A. Gschneidner, Effect of alloying on the giant magnetocaloric
EP
TE D
M AN U
SC
RI PT
effect of Gd5(Si2Ge2), J. Magn. Magn. Mater.167(1997) L179–L184.
AC C
[31]
ACCEPTED MANUSCRIPT Table 1. Unit-cell, positional and thermal parameters and discrepancy factors after the refinement of the crystal structure from NPD data at RT of La0.67Sr0.22Ba0.11Mn1-xFexO3. Cristallite size is also included. 0
0.1
0.2
0.3
Space group
Pnma
R-3c
R-3c
R-3c
a(Å)
5.4587(6)
5.5152 (2)
5.51264(7)
5.51699(7)
b(Å)
7.7177(12)
-
-
-
c(Å)
5.5271(7)
13.3972(7)
13.4135(2)
13.4216(2)
V(Å3)/Z*
58.21(1)
58.82(1)
58.84(1)
58.96(1)
La/Ba/Sr
4c (x, 1/4 , z)
6a (0, 0, 3/4)
x
0.0020(5)
z
-0.0258(1)
B(Å2)
0.93(8)
Mn/Fe
4b (0, 0, 1/2)
6b (0, 0, 0)
B(Å2)
0.34(9)
0.30
M AN U 0.44(6)
TE D
O1
SC
Cell parameters
RI PT
Fe content (x)
0.55(3)
0.54(3)
0.30
0.30
4c (x, 1/4 , z)
18e (x, 0, 1/4)
0.4989(9)
0.4625(3)
0.4627(1)
0.4644(1)
1.24(4)
1.20(2)
1.10(2)
0.7617(1)
-
-
-
0.02148(5)
-
-
-
0.2485(6)
-
-
-
1.6(2)
-
-
-
Rp
5.59
4.89
2.89
2.77
Rwp
7.96
6.96
3.65
3.46
Rexp
1.84
2.16
1.92
2.21
EP
x
0.0073(1)
z 2
B(Å )
AC C
O2
0.74(9)
x y z 2
B(Å )
8d (x ,y ,z)
Discrepancy factors (%)
ACCEPTED MANUSCRIPT 18.7
10.4
3.63
2.46
RBragg
5.91
5.21
3.08
3.01
Crystallite Size 28.19 32.31 28.8 D(nm) *Z: formula units per unit cell; Z= 4 for Pnma; Z= 6 for R-3c
33.97
Table
2.
Main bond
distances
(Å)
and
RI PT
χ2
selected
Fe content (x)
0
0.1
Bond distances 1.9299(3)
Mn-O2
1.911(2)
Mn-O2
1.989(2)
Angles 177.55(4)
Mn-O2-Mn
169.81(10)
EP AC C
1.9546(6)
(deg)
0.3
1.9569(4)
-
-
-
-
-
-
167.858(10)
167.963(4)
168.478(3)
-
-
TE D
Mn-O1-Mn
1.9555(4)
0.2
M AN U
Mn-O1
SC
La0.67Sr0.22Ba0.11Mn1-xFexO3 at RT.
angles
-
for
ACCEPTED MANUSCRIPT Table 3. Maximum entropy change │∆SMax│ and relative cooling power (RCP), for La0.67Sr0.22Ba0.11MnO3 and La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 compounds, occurring under magnetic field variations, compared to several materials considered for magnetic refrigeration
5 5 5 5 5 5 5 5
EP AC C
(J/KgK) 2.46 2.43 0.91 2.26 1.48 3 5 9.5
Rcp (J/Kg) 169 241 70 153 161 132 200 410
Reference
RI PT
360 268 94 190 292 290 328 293
TE D
La0.67Sr0.22Ba0.11MnO3 La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 La0.67Sr0.22Ba0.11Mn0.8Fe0.2O3 La0.67Ba0.22Sr0.11Mn0.9Fe0.1O3 La0.67Ba0.33MnO3 La0.67Sr0.33Mn0.9Ni0.1O3 La0.67Sr0.33Mn0.9Ni0.1O3 Gd
µ 0∆H (T)
SC
Tc (K)
M AN U
Sample
This work This work This work [17] [28] [29] [30] [31]
ACCEPTED MANUSCRIPT Figure captions Fig. 1. X-ray diffraction patterns of La0.67Sr0.22Ba0.11Mn1-xFexO3 compounds, Rietveld refined with the model derived from NPD data. a) x= 0, b) x= 0.1, c) x= 0.2, c) x= 0.3.
Fig. 2. Observed (crosses), calculated (full line), and difference (bottom) NPD Rietveld
Bragg positions. a) x= 0, b) x= 0.1, c) x= 0.2, c) x= 0.3.
RI PT
profiles for La0.67Sr0.22Ba0.11Mn1-xFexO3 (0≤x≤0.3) at 298 K. Vertical lines correspond to the
Fig. 3. View of the orthorhombic (Pnma) crystal structure of La0.67Sr0.22Ba0.11MnO3 and the
SC
coordination polyhedron of Mn displaying the Mn-O distances.
M AN U
Fig. 4. View of the rhombohedral (R-3c) crystal structure of La0.67Sr0.22Ba0.11MnO3 and the coordination polyhedron of Mn displaying the equal Mn-O distances.
Fig. 5. (a) Variation of cell unit volume and the average bond distances with x, (b) variation of the average bond angles with the Fe content. Fig. 6. Typical scanning electron micrographs of La0.67Sr0.22Ba0.11Mn1-xFexO3 samples; (a) x=
TE D
0, (b) x=0.1, (c) x=0.2 and (d) x=0.3
Fig. 7. Temperature dependence of ZFC and FC magnetization data taken at H= 1000 Oe for:
EP
(a) x=0, x=0.1; (b) x=0.2, x=0.3; the inset represents dM/dT versus T curves, to determine TC. Fig. 8. Magnetization vs Field isotherms near TC for La0.67Sr0.22Ba0.11Mn1-xFexO3 (x=0, 0.1
AC C
and 0.2) samples
Fig. 9. Arrott plots around TC for La0.67Sr0.22Ba0.11Mn1-xFexO3 (x=0 and 0.1) samples. Fig. 10. Thermal evolution of the entropy under different amplitudes of change in the magnetic
field
(from
bottom
to
top
∆H=1
T,
2T,
3T,
4T,
and
5T)
for
La0.67Sr0.22Ba0.11Mn1-xFexO3. a) x=0, b) x= 0.1 and x=0.2. Fig.11. Relative cooling power values (RCP) versus applied magnetic field for La0.67Sr0.22Ba0.11Mn1-xFexO3 (x = 0, 0.1 and 0.2) compounds.
ACCEPTED MANUSCRIPT
AC C
EP
b
TE D
M AN U
SC
RI PT
a
Fig.1
ACCEPTED MANUSCRIPT
AC C
EP
d
TE D
M AN U
SC
RI PT
c
Fig.1
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
a
AC C
EP
TE D
b
Fig.2
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
c
AC C
EP
TE D
d
Fig.2
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.3
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.4
ACCEPTED MANUSCRIPT
1,960 59,0
a 1,955
RI PT
1,950
1,945
58,6
1,940
1,935
SC
58,4
M AN U
58,2 0,0
0,1
0,2
1,930 0,3
x
TE D
b
171,0
EP
172,5
AC C
(deg)
174,0
169,5
168,0
0,0
0,1
0,2
X
Fig.5
0,3
(A°)
3 V (A° )
58,8
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.6
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.6
ACCEPTED MANUSCRIPT 0,4
80
FC (x=0) FC (x=0.1)
a 0,0
dM/dT
70
50
Tc=232K
-0,4
RI PT
-0,8
Tc=360K
40 -1,2 0
30
200
400
20
SC
T (K)
x=0(FC ) x=0(ZFC ) x=0.1(FC ) x=0(ZFC )
10 0 0
100
200
M AN U
M(emu/g)
60
300
400
500
600
700
b
10
EP
x = 0 .2 (Z F C ) x = 0 .2 (F C ) x = 0 .3 (Z F C ) x = 0 .3 (F C )
6
AC C
M(emu/g)
8
TE D
T(K )
4
2
0 0
Fig.7
100
200
T (K )
300
ACCEPTED MANUSCRIPT 50
300K
x=0
30
∆T=8T
RI PT
M(emu/g)
40
20
10
0 0
1
2
3
µ 0 H (T ) x = 0 .1 70 60
M(emu/g)
50 40
5
5K 180K
∆T=8K
TE D
30
4
a
M AN U
80
SC
420K
20 10 0
1
EP
0
2
280K 300K
b 3
4
5
µ 0 H (T )
50K
x = 0 .2
AC C
40
M(emu/g)
30
∆T=8K
20
200K 10
c 0 0
Fig.8
1
2
3
µ 0 H (T )
4
5
ACCEPTED MANUSCRIPT
300K
x=0
RI PT
2000
2
-2
M (emu g )
1500
1000
500
0 0,00
0,08
0,16
M AN U
2
SC
∆ T=8K
0,24
0,32
30 0 0
x = 0 .1 25 0 0
g)
∆ T= 8 K
10 0 0
280K
500
0 0 ,00
0 ,0 4
b 0 ,0 8
0,1 2
0 ,1 6
µ 0 H /M (T e m u
Fig.9
0,48
180K
EP
15 0 0
0,40
AC C
2
2
-2
M (emu g )
20 0 0
-1
a
TE D
µ 0 H /M (T em u
420K
0 ,2 0 -1
g)
0 ,2 4
0 ,2 8
ACCEPTED MANUSCRIPT 1T 2T 3T 4T 5T
a
2 ,4
1 ,6
1 ,2
M
-∆ S (J/Kg.K)
2 ,0
0 ,4
0 ,0 300
320
340
360
380
2 ,4
b
M AN U
2 ,0
1 ,6
1 ,2
M
-∆ S (J/Kg.K)
400
SC
T (K )
RI PT
0 ,8
0 ,8
0 ,0 180
200
220
240
260
280
c
M
-∆S (J/Kg.K)
300
1T 2T 3T 4T 5T
AC C
0 ,8
1T 2T 3T 4T 5T
T (K )
EP
1 ,0
TE D
0 ,4
420
0 ,6
0 ,4
0 ,2
0 ,0 40
60
80
100
120
T (K )
Fig.10
140
160
180
200
250
M AN U
SC
x=0 x=0.1 x=0.2
200
Rcp (J/Kg)
RI PT
ACCEPTED MANUSCRIPT
150
100
0
2
AC C
EP
1
TE D
50
Fig.11
3
µ0H (T)
4
5
ACCEPTED MANUSCRIPT HIGHLIGHTS
-Novel Fe-doped manganite oxides prepared by a sol-gel procedure
- Ferromagnetic behavior for x= 0, 0.1; spin glass for x= 0.2, 0.3
RI PT
- Neutron diffraction shows a phase transition upon Fe introduction, since tolerance factor increases
AC C
EP
TE D
M AN U
SC
- Magnetocaloric effect enhanced for x=0.1; improved “relative cooling power” respect x=0
S0925-8388(15)30431-X
DOI:
10.1016/j.jallcom.2015.07.034
Reference:
JALCOM 34723
To appear in:
Journal of Alloys and Compounds
Received Date: 21 April 2015 Revised Date:
29 June 2015
Accepted Date: 3 July 2015
Please cite this article as: R. Ben Hassine, W. Cherif, J.A. Alonso, F. Mompean, M.T. FernándezDíaz, F. Elhalouani, Enhanced Relative Cooling Power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.07.034. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Graphical abstract
Enhanced Relative Cooling Power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties. J.A. Alonso, F. Mompean M.T. Fernández-Díaz, F.
RI PT
R. Ben Hassine, W. Cherif,
EP
TE D
M AN U
SC
Elhalouani
AC C
The title perovskites present a crystallographic phase transition from an orthorhombic structure (Pnma) for x=0 to a rhombohedral structure (R-3c) for Fe-doped samples, as shown in a neutron study. Magnetic data show that x = 0 and x = 0.1 perovskites exhibit sharp paramagnetic-ferromagnetic transitions. The relative cooling power (RCP) is as high as 241 J.Kg-1 for x= 0.1, being a promising candidate for magnetic refrigeration.
ACCEPTED MANUSCRIPT
Enhanced Relative Cooling Power of Fe-doped La0.67Sr0.22Ba0.11Mn1-xFexO3 perovskites: Structural, magnetic and magnetocaloric properties. R. Ben Hassine,a W. Cherif,
a
J.A. Alonso,b* F. Mompean,b M.T. Fernández-Díaz,c F.
RI PT
Elhalouani d a
Sfax University, Faculty of Sciences, B. P. 1171 - 3000, Tunisia.
b
Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones
Científicas, Cantoblanco, E-28049 Madrid, Spain. d
SC
Institut Laue-Langevin, B.P. 156, F-38042 Grenoble Cedex 9, France
Sfax University, National School of Engineers, B. P. W 3038, Tunisia.
M AN U
c
Abstract:
We present the structural and magnetic properties of a novel series of La0.67Sr0.22Ba0.11Mn1-xFexO3 (0≤x≤0.3) perovskites prepared by the sol-gel method. These oxides were characterized by x-ray (XRD), neutron powder diffraction (NDP) at room
TE D
temperature and magnetization measurements versus temperature and various applied magnetic fields. The NPD data, very sensitive to the octahedral tilting, show a crystallographic phase transition from an orthorhombic structure (Pnma) for x=0 to a rhombohedral structure (R-3c) for Fe-doped samples. Magnetic data show that x = 0 and x =
EP
0.1 perovskites exhibit a paramagnetic-ferromagnetic transition at low temperature, while for 0.2≤x≤0.3 a strong divergence between ZFC and FC curves suggest the presence of
AC C
antagonistic antiferromagnetic and ferromagnetic interactions. The magnetic entropy change (│∆Smax│) takes values of 2.46 J Kg-1 K-1, 2.43 J Kg-1 K-1 and 0.91 J Kg-1 for x = 0, x = 0.1 and 0.2 , respectively at 5 T . The relative cooling power (RCP) amounts 169 J.Kg-1, 241 J.Kg-1 and 70 J.Kg-1 at 5 T for x= 0, 0.1, 0.2 respectively. These values are compared favorably
with
those
of
some
others
reported
manganites,
making
La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 a promising candidate for magnetic refrigeration. Keywords: Sol gel, X-Ray diffraction, Neutron diffraction, Curie temperature, Magneto caloric effect
ACCEPTED MANUSCRIPT *Corresponding autor. Email : [email protected]
1-Introduction:
perovskite
ABO3-type
manganites
with
the
general
formula
RI PT
Recently,
,where Ln is a rare earth (Ln = La, Pr…) and A is a divalent alkali-earth element (A= Ca, Sr, Ba……), have been the subject matter of a large number of studies due to their interesting structural and magnetic properties [1]. These perovskites are
SC
simultaneously metallic and ferromagnetic below Curie temperatures close to room temperature, by virtue of a well-known double-exchange effect.
M AN U
Given their ferromagnetic properties, many works on the magnetocaloric effect (MCE) involving perovskite-type rare-earth manganites have attracted considerable attention of the scientific community over the past years, due to their potential applications [2-3], such as magnetic refrigeration (MR). Comparing with the gas compression refrigeration, this technology exhibits significant advantages such as high efficiency and minimal environmental
TE D
impact [4,5]. The magnetocaloric effect (MCE) is characterized by the isothermal change of the magnetic entropy and the adiabatic change of temperature, induced by the application of an external magnetic field [5]. The main requirements for a magnetic material to possess a large │∆SM│, are a large spontaneous magnetization as well as a sharp drop in the
EP
magnetization associated with the ferromagnetic to paramagnetic transition at the Curie temperature TC [6,7].
AC C
The MCE property is usually explained by the double exchange interaction (DE)
between the trivalent (Mn3+) and tetravalent (Mn4+) ions [8] contained in mixed-valence manganites. To enhance this property many studies have discussed the effect of Fe doping on the structural and magnetic properties. Such manganites have a complex band structure containing trivalent Mn3+ and trivalent Fe3+ ions occupying both octahedral (B) sites [9,10]. The substitution of Mn ions by Fe ions in AMn1-xFexO3 manganites, introduces lattice distortions but also reduces the Mn3+/Mn4+ ratio.
In this work, we present the effect of the substitution of the Mn ions by Fe ions on the structural and magnetic properties of La0.67Sr0.22Ba0.11Mn1-xFexO3 (0 ≤ x ≤ 0.3) compounds
ACCEPTED MANUSCRIPT and the magnetocaloric effect for the La0.67Sr0.22Ba0.11MnO3 , La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 and La0.67Sr0.22Ba0.11Mn0.8Fe0.2O3 samples. In this perovskite series we have optimized TC by doping with 33% of alkali-earth cations at the A positions of the perovskite, and we have increased the tolerance factor by partially replacing Sr by Ba: the larger ionic radius of Ba2+ ions leads to an increase of the perovskite symmetry, opening of the superexchange Mn-O-
RI PT
Mn angles between octahedral units, thus favouring double exchange, enhancing the ferromagnetic interactions and hence the Curie temperature. The structural analysis from NPD data show interesting features, neutrons being sensitive to the oxygen positions and thus allowing determining the tilting systems and Mn-O distances and Mn-O-Mn angles with
upon Fe doping the Mn position of the perovskites.
M AN U
2-Experimental
SC
precision; these data have been essential to correctly characterize a phase transition observed
Samples with nominal composition La0.67Sr0.22Ba0.11Mn1-xFexO3 (x= 0, 0.1, 0.2, 0.3) were synthesized by the sol–gel method from MnCO3, La2O3, SrCO3, BaCO3 and Fe2O3 (99.9% purity) in the appropriate stoichiometric proportions. The powders were dissolved in
TE D
nitric acid, HNO3. Suitable amounts of citric acid and ethylene glycol as a chelating agent were added until a completely homogeneous and transparent solution was achieved. At this stage, the PH is considerably acid, around 1.2. During the subsequent gentle heating leading to the evaporation of the solvent and partial elimination of HNO3 as NO2 vapors the PH
EP
increases until 1.5, when the resin is formed. After slowly drying the solution, it was decomposed at 600ºC in air. Finally, the resulting powders were annealed in air at 1000 °C.
AC C
The structure, phase purity and homogeneity of the as-elaborated samples were checked by Xray powder diffraction (XRD) using CuKα radiation (λ = 1.54056 Å) and neutron powder diffraction (NPD). The crystallographic structures were refined from high resolution NPD patterns collected at the Institut Laue-Langevin (ILL) in Grenoble (France), acquired at room temperature at the D2B diffractometer with λ=1.594(1) Å. About 3 grams of each sample were contained in vanadium cylinders; the counting time was 2 hours for each data collection in the high-intensity mode. The diffraction data were analyzed by the Rietveld method using the FULLPROF program [11] and the average particle size was determined using the Scherrer formula implemented in this software. A pseudo-Voigt function was chosen to generate the line shape of the diffraction peaks. The background was approximated with a 5th-degree polynomial.
ACCEPTED MANUSCRIPT The following parameters were refined in the final runs: scale factor, background coefficients, zero-point error, pseudo-Voigt corrected for asymmetry parameters, positional coordinates, isotropic displacement factors and mixed occupancy factors of Mn/Fe. The coherent scattering lengths for La, Sr, Ba, Mn, Fe, and O were 8.240, 7.02, 5.07, -3.438, 9.45 and 5.805 fm,
RI PT
respectively.
Magnetic measurements were performed on a commercial SQUID magnetometer from Quantum Design; the dc magnetic susceptibility was recorded in the temperature range 5-450 K in ZFC and FC runs with an applied field of 0.1 T with a heating rate of 5 K min-1;
SC
magnetization isotherms were collected between –50 kOe and +50 kOe with ∆T= 8K between 300 to 420 K (x= 0) and 180 to 260 K (x= 0.1). The magnetic entropy changes |∆SM| were
3-Results and discussion 3.1 Crystallographic structure
M AN U
estimated from the magnetization data using a Maxwell relation.
TE D
Fig. 1 shows the XRD patterns of the four compounds described in this work. They show reflections characteristic of pure perovskite phases. They have been Rietveld-refined with the structural models derived from NPD data, described immediately below. No impurity phases
EP
are observed in any of the diagrams. From XRD data it is difficult to determine any deviation from the cubic symmetry, since the structural distortion is weak and the superstructure
AC C
reflection are almost invisible, hence NPD are required. The NDP analysis for La0.67Sr0.22Ba0.11Mn1-xFexO3 (0≤x≤0.3) helped to assess the true symmetry and structural features of these oxides. For x= 0 the pattern can be refined in the standard orthorhombic (Pnma) space group, whereas for x ≥ 0.1 a symmetry change is observed, and the crystal structures need to de defined in the rhombohedral R-3c space group A structural transition is thus identified as Fe is introduced into the crystal structure. Similar results were observed by Tlilia and al. in ref [12] in the La0.75Ca0.08Sr0.17 Mn1-xFexO3 series. The crystal structure of La0.67Sr0.22Ba0.11MnO3 was indexed in an orthorhombic unit cell with unit-cell parameters related to a0 (ideal cubic perovskite, a0≈ 3.8 Å) as a≈c≈√2a0; b≈ 2a0, in
ACCEPTED MANUSCRIPT the Pnma space group. In this model La, Sr and Ba are distributed at random over the 4c (x,1/4,z) positions, Mn atoms occupy a single position at 4b (0,0,1/2) Wyckoff sites, and there are two independent positions for oxygens, O1 (4c) and O2 (8d). The lattice parameter values obtained in the fitting are presented in Table 1, as well as the atomic positions; some selected interatomic distances (Mn-O bond distances) and Mn-O-Mn bond angles are listed in
RI PT
Table 2. The good agreement between experimental and calculated XRD and NDP profiles after the Rietveld refinements are displayed in Figs. 1a and 2a, respectively. No extra peaks were detected in the XRD or NPD patterns that could indicate the presence of impurities in the sample.
SC
For x ≥ 0.1 a phase transition to a rhombohedral R-3c symmetry is observed; in this structure La, Ba and Sr are randomly distributed at 6a (0,0,1/4) sites, Mn and Fe statistically distributed
M AN U
over the 6b (0,0,0) positions and a single type of oxygen atoms O1 at 18e (x,0,1/4). The unit cell and atomic parameters, as well as discrepancy factors after the refinement from NPD data, and main interatomic distances and angles are gathered at Table 1. The goodness of the fit for the three compounds with x= 0.1, 0.2 and 0.3 are displayed at Figs. 1b-d for XRD data
TE D
and Figs. 2b-d for NPD data, respectively. No impurities appear at any XRD of NPD pattern.
Fig. 3 and Fig. 4 display two views of the orthorhombic (x= 0) and rhombohedral (x = 0.1) structures, highlighting the occurrence of deformed octahedra for the orthorhombic perovskite, allowing for the manifestation of a Jahn-Teller distorsion corresponding to the
EP
presence of 67% of Mn3+ ions (as derived from the nominal doping), whereas for the rhombohedral phase this distortion is not allowed for the symmetry of the space group, the
AC C
octahedra containing six equivalent Mn-O distances, as observed in a previous work [13].
Fig. 5a exhibits the variation of unit-cell volume for a single perovskite unit (taking into account that Z= 4 and 6 for the Pnma and R-3c space groups, respectively),
ACCEPTED MANUSCRIPT volume and
RI PT
the concomitant increase of symmetry upon Fe introduction into the lattice, driving a structural phase transition from an orthorhombic to rhombohedral symmetry.
Whereas the Pnma space group involves a-b+c- tilting of the octahedra (in antiphase along the
SC
a and c directions of the aristoptype, and in phase along the long b-axis direction), the R-3c space group allows cooperative octahedral-site tilting along the [111] direction of the primary unit cell or the c axis in the hexagonal cell. A few perovskite oxides A3+B3+O3 with t ≤ 1
M AN U
adopt the R-3c crystal structure at ambient pressure, i.e. RAlO3 (R= La, Pr, Nd), LaCoO3, LaNiO3, LaCuO3, LaGaO3 (at T > 540 K). The rhombohedral phase can also be stabilized under pressure: the X-ray powder diffraction of LaMnO3 under 12 GPa can be refined well with the R-3c structure [16]. In the present case we have seen that subtly modifying the B octahedral sublattice with suitably chosen elements also drives the mentioned increased in
TE D
perovskite symmetry. In the present case this has the advantage of increasing the superexchange Mn-O-Mn angles (Fig. 5b), improving the overlap between Mn 3d and O 2p orbitals and thus enhancing the magnetic interactions, which are the properties of interest of
EP
the present materials.
It is interesting to compare the present compounds with La0.67Ba0.22Sr0.11Mn1-xFexO3 (x = 0,
AC C
0.1, 0.2, 0.3 and 1.0) described in Ref. [17]. In this system the samples with x≤ 0.3 are described as orthorhombic from XRD data, contrasting with the present perovskites, where NPD data, very sensitive to the octahedral tilting, unveil a crystallographic phase transition from an orthorhombic structure (Pnma) for x=0 to a rhombohedral structure (R-3c) for Fedoped samples. Comparing the undoped x=0 compounds we observe that the size of the unit cell decreased from V/Z*=59.17 Å3 for La0.67Sr0.11Ba0.22MnO3 [17] to 58.21 Å3 for the present La0.67Sr0.22Ba0.11MnO3 perovskite, which is expected from the larger ionic size of Ba2+ vs Sr2+. In our case we could detect from the neutron study that the samples experienced a transition to a rhombohedral symmetry for Fe-doped compounds; the higher tolerance factor for the Ba0.22 series [17] would have led to a similar transition; however from the XRD patterns the
ACCEPTED MANUSCRIPT authors could not detect such a subtle feature, which is not surprising given the fair crystallinity of their samples.
We employed the Scanning Electron Microscopy (SEM) in order to examine the morphology
RI PT
of the La0.67Sr0.22Ba0.11Mn1-xFexO3 samples (x = 0, 0.1, 0.2, 0.3 and 1.0). SEM images reveals the presence of some pores in the samples, probably related to the preparation procedure from citrate precursors, and a good connectivity between the grains.
M AN U
SC
The average crystallite size was estimated from the NDP data using the Scherrer relation [18]:
Here K, ᵝ, λ, and Ѳ are the grain shape factor, the X-ray wavelength, the full width at half maximum (FWHM) of the diffraction peak, and the Bragg diffraction angle, respectively. The values of the effective crystallite sizes are summarized in Table 1. In all cases a nanometric size for the crystallites is found, around 30 nm, which is related to the moderate synthesis
procedures.
EP
3.2 Magnetic properties
TE D
temperatures of these samples, of 1000ºC, obtained from very reactive precursors from sol-gel
The ZFC and FC M(T) curves are presented in Fig. 7. Fig. 7a shows the thermal
AC C
variation of the susceptibility for x=0 and 0.1 samples; both exhibit a ferromagnetic (FM) to paramagnetic (PM) phase transition as the temperature increased. The Curie temperature TC, can be determined by the minimum of dM/dT at the inflection point of the FC M(T) curve. The Curie temperature decreased with doping iron from 360 K to 232 K for La0.67Sr0.22Ba0.11MnO3 and La0.67Sr0.22Ba0.11Fe0.1Mn0.9O3, respectively. Interestingly, the TC for x= 0 is well above RT, as expected for the high tolerance factor of this perovskite, containing both Sr and Ba ions at the A sublattice; this ferromagnetic behavior is due to the double exchange effect associated with the mixed Mn valence at the octahedral sublattice (nominally 66% Mn3+ 33% Mn4+). The introduction of Fe very fast perturbs the double exchange leading to a decrease of the Curie temperature, since the presence of Fe3+ establishes antiferromagnetic interactions in the octahedral sublattice. Yet, in our samples the
ACCEPTED MANUSCRIPT decrease of TC per 1% Fe doping is approximately 13 K, smaller from that obtained for the Nd0.67Sr0.33Mn1-xFexO3 system [19,20], where a drop of 18 K per 1% Fe was observed. The M(T) curves for the samples x=0.2 and x=0.3 show that the magnetization progressively decreases (Fig. 7b). At a temperature Tm, indicated by arrow in Fig. 7b, a bifurcation between
RI PT
the FC and ZFC curves (λ shape) is observed ,which is generally associated in the literature of manganites with the appearance of antiferromagnetic interactions antagonistic with the ferromagnetic double-exchange interactions. These interactions sometimes give rise to a glass magnetic state, with a spin- or cluster-like freezing process [21,22]. However, this could also
SC
be a result of the magnetic anisotropy and other authors consider that the competition between the ferromagnetic DE interactions and the coexisting anti-ferromagnetic super exchange interactions with the introduction of Fe3+ for Mn3+ could drive the system supposedly into a
M AN U
random canted ferromagnetic state at low temperatures [23].
In comparison with the magnetic properties of the La0.67Sr0.11Ba0.22Mn1-xFexO3 series [17], we found that the Curie temperature for La0.67Sr0.22Ba0.11MnO3 (360 K) is higher than that of La0.67Sr0.11Ba0.22MnO3 (TC= 345 K [17]); the shorter Mn-O distances observed in the former
TE D
perovskite account for the enhanced FM interactions found in the present perovskite oxide. As observed in the present series, an even sharper decrease of the Curie temperature upon Fe doping is reported in Ref [17], also explained by the appearance of AFM Fe-O-Fe and Fe-OMn superexchange interactions competing with the FM double exchange; for instance, for x=
AC C
K.
EP
0.1, TC= 190 K [17] in contrast with the present La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 with TC= 268
3.3 Magnetic caloric effect
Fig. 8(a-b) show isothermal magnetization curves for La0.67Sr0.22Ba0.11MnO3 and
La0.67Sr0.22Ba0.11Fe0.1Mn0.9O3 samples (hereafter called LSBMO and LSBMFO, respectively), measured under applied magnetic fields ranging between 0-5 T and at temperatures spanning from 300 to 420 K and 180 to 300 K, respectively. The isothermal magnetization M (H, T) magnetic field dependency, measured at different temperatures below TC, shows a non-linear behavior with a sharp increase for low field values and a tendency to saturation as the
ACCEPTED MANUSCRIPT magnetic field increases, reflecting a ferromagnetic behavior. Beyond the Curie temperature, the material follows a paramagnetic behavior in which the ferromagnetic order is broken, due to the random reorientation of the magnetic moments for to thermal agitation [24]. In Fig. 9a and 9b displays the Arrott curves (µ 0H/M vs M2) for LSBMO and
RI PT
LSBMFO deduced from isothermal magnetization curves recorded around TC for both samples in a magnetic field up to 5 T. According to Banerjee’s criterion [25], a negative or positive sign of the slope of Arrott curves corresponds to a first-order or second-order magnetic phase transition, respectively. The results obtained from µ 0H/M versus M2 plots of
SC
LSBMO and LSBMFO show a positive slope in all cases in the complete M2 range, confirming that a second-order FM to PM phase transition has occurred.
M AN U
The temperature dependence of│∆SM│ has been determined from the M (H) isotherms. Figure 10a and b show the magnetic entropy change │∆SM│ for both samples as a function of temperature under different magnetic fields: 1,2,3,4 and 5T. From the M (H, T) data, the magnetic entropy change for our samples can be calculated as [26]:
TE D
(1)
In the case of magnetization measurements at small discrete field and temperature intervals,
EP
numerical approximation of the integral in Eq. (1) could be approximated as [27]:
AC C
(2)
where Mi and Mi+1 are the experimental data of the magnetization Ti and Ti+1, under a magnetic field Hi.
In Fig. 8a, b and c we observe that |∆SM| increases with an increasing applied magnetic field, the maximum entropy change corresponding to a magnetic field variation of 1, 2, 3, 4 and 5 T for
La0.67Sr0.22Ba0.11MnO3
is
0.35;
0.98;
1.49;
1.97;
2.46
JKg-1K-1,
for
La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 it is 0.48; 1.02; 1.42; 1.82; 2.43 JKg-1K-1 and for La0.67Sr0.22Ba0.11Mn0.8Fe0.2O3 it is 0.09; 0.28; 0.48; 0.68; 0.91 JKg-1K-1, respectively.
ACCEPTED MANUSCRIPT The magnetic cooling efficiency of a magnetocaloric material is evaluated by considering the relative cooling power (RCP) [28] given by:
RI PT
where │∆Smax│ is the maximum entropy change at TC and is equal to δTFWHM = (T2-T1), the full-width temperature span of the |∆SM| versus temperature plots at their half-maxima. The results of this estimation are show in Fig 11. The Rcp values exhibit a linear increase with increasing field for all compounds. For our samples, the Rcp values are 169 J.Kg-1, 241
SC
J.Kg-1 and 70 J.Kg-1 at 5 T for x= 0, 0.1, 0.2 respectively.
In Table 3 the present results are compared with those of similar systems (perovskite
M AN U
manganites) taken from the literature, achieving weaker responses than those described here. The Rcp of La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 compound is higher than those obtained by F. Ben Jemaa et al [17] for La0.67Sr0.11Ba0.22Mn0.9Fe0.1O3 prepared by sol-gel method, superior than La0.67Sr0.22Ba0.11MnO3 oxide reported by D.T. Morelli et al [30] and, in general, better than all perovskite oxides, only overcome by Gd metal [31]. The replacement of Mn by Fe ions is
TE D
certainly advantageous, as shown in Table 3, with respect to Mn-only containing compounds. The values of Rcp are extended over a wide range of temperature around the Curie temperatures and hence these materials are useful for near-room-temperature magnetic
AC C
4. Conclusion
EP
refrigeration applications.
La0.67Sr0.22Ba0.11Mn1-xFexO3 compounds were prepared by sol–gel method and
sintered at 1000 °C, yielding nanometric powders. NPD data show that these perovskites crystallize, for x= 0, in an orthorhombic structure (Pnma space group) and undergo a transition to a rhombohedral superstructure of perovskite (R-3c) for Fe contents x≥ 0.1. This is due to the increment of the average <(Mn,Fe)-O> distances in the octahedral positions, leading to a concomitant increase of the tolerance factor of the perovskite. Magnetic measurements show a ferromagnetic behavior for x=0 (TC= 360 K) and 0.1 (TC= 232 K) samples, whereas compounds with x≥0.2 present a divergence of FC and ZFC curves due to the appearance of antagonistic antiferromagnetic interactions upon introduction of Fe3+
ACCEPTED MANUSCRIPT moments, that compete with the double exchange effect associated with the mixed Mn3+,4+ valence. The relative cooling power Rcp is 168 (J Kg-1) and 241 (J Kg-1) for the samples x=0 and x=0.1 under ∆H= 5T respectively. Hence, the compound doped by Fe (x=0.1) is a candidate for magnetic refrigerant, performing better than most related perovskites.
RI PT
Acknowledgements
We acknowledge the financial support of the Spanish Ministry of Economy and Competitivity
AC C
EP
TE D
M AN U
SC
the project MAT2013-41099-R. We are grateful to ILL for making all facilities available.
ACCEPTED MANUSCRIPT References [1]
R. Von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer, Phys. Rev. Lett. 71 (1993) 2331.
[2]
S. Othmani, R. Blel, M. Bejar, M. Sajieddine, E. Dhahri, E.K. Hlil, Solid State
RI PT
Commun. 149 (2009) 969. [3]
L. Li, K. Nishimura, M. Fujii, K. Mori, Solid State Commun. 144 (2007) 10.
[4]
O. Tegus, E. Bruck, K.H.J. Buschow, F.R. de Boer, Transition-metal- based magnetic refrigerants for room-temperature applications, Nature 415 (2002) 150–152.
A.M. Tishin, I. Spichkin, The Magnetocaloric Effect and its Applications, Institute of Physics Publishing, Bristol, 2003.
S.Y. Dan’kov, A.M. Tishin, V.K. Pecharsky, K.A. Gschneidner, Phys. Rev. B57
M AN U
[6]
SC
[5]
(1998) 3478. [7]
M.H. Phan, S.C. Yu, N.H. Hur, Appl. Phys. Lett. 86 (2005) 072504.
[8]
C. Zener, Interaction between the d shells in the transition metals, Phys. Rev. 81(1951)440–444.
[9]
G.H. Rao, J.R. Sun, A. Kattwinkel, L. Haupt, K. Baerner, E. Schmitt, E. Gmelin,
[10]
TE D
Physica B 269 (1999) 379.
M. Sugantha, R.S. Singh, A. Guha, A.K. Raychaudhuri, C.N.R. Rao, Mater. Res. Bull. 33 (1998) 1129.
J. Rodríguez-Carvajal, Physica B (Amsterdan) 192 (1993) p. 55.
[12]
M.T. Tlili, M. Bejar, E. Dhahri, M. Sajieddine, M.A. Valente, E.K. Hlil, Materials
EP
[11]
Characterization. 62 (2011) 243-247. M. Ellouze, W. Boujelben, A. Cheikhrouhou, H. Fuess, R. Madar, Solid State
AC C
[13]
Commun. 124 (2002) 125.
[14] [15]
R.D. Shannon, Acta Cryst. A, 32, (1976) 751.
A. Muñoz, J. A. Alonso, M. J. Martínez-Lope, and J. L. Martínez, Phys. Rev. B 72, 184402 (2005).
[17]
F. Ben Jemaa, S. Mahmood , M. Ellouze , E.K. Hlil, F. Halouani , I. Bsoul , M. Awawdeh, J. Solid State Sci. 37 (2014) 121-130.
[18]
A. Guinier, in: X. Dunod (Ed.), Theorie et Technique de la Radiocristallographie, p. 482. third ed., 1964
[19]
J. Takeuchi, S. Hirahara, T.P. Dhakal, K. Miyoshi, K. Fujiwara, Colossal
ACCEPTED MANUSCRIPT magnetoresistance of perovskite Nd0.67Sr0.33Mn1-xFexO3 single crystals, J. Magn. Magn. Mater. 226–230 (2001) 884–885. [20]
Y.L. Chang, Q. Huang, K. Ong, Effect of Fe doping on the magnetotransport properties in manganese oxides, J. Appl. Phys. 91 (2002) 789–793.
[21]
J.A. Mydosh, Spin-Glass: An experimental Introduction, Taylor& Francis, London,
[22]
RI PT
1993. M. Baazaoui, S. Zemni, M. Boudard, H. Rahmouni, A. Gasmi, A. Selmi, M. Oumezzine, Magnetic and electrical behaviour of La0.67Ba0.33Mn1-xFexO3 perovskites,
[23]
SC
Mater. Lett. 63 (2009) 2167–2170.
D. C. Kundaliy, R. Vij, R.G. Kulkarni, A.A. Tulapurkar, R. Pinto, S.K. Malik, W.B. Yelon,
Structural,
magnetic
and
magnetotransport
properties
of
the
Materials, 264, 2003, 62–69.
[24]
M AN U
La0.67Ca0.33Mn0.9Fe0.1O3 perovskite, Journal of Magnetism and Magnetic
B. Arayedh, S. Kallel, N. Kallel, O. Peña, Influence of non-magnetic and magnetic ions on the Magneto-Caloric properties of La0.7Sr0.3Mn0.9M0.1O3 doped in the Mn sites
TE D
by M= Cr, Sn, Ti, J. Magn. Magn. Mater. 361 (2014) 68–73. [25]
S.K. Banerjee, Phys. Lett. 12 (1964) 16.
[26]
X. Bohigas, J. Tejada, M.L. Martinez-Sarrión, S. Tripp, R. Black, Magnetic and calorimetric measurements on the magnetocaloric effect in La0.6Ca0.4MnO3, J. Magn.
[27]
EP
Magn. Mater. 208 (2000) 85–92.
R.D. McMichael, J.J. Ritter, R.D. Shull, Enhanced magnetocaloric effect in Gd3Ga5-xFexO12, J. Appl. Phys. 73 (1993) 6946–6948. M.H. Phan, S.C. Yu, Review of the magnetocaloric effect in manganite materials, J.
AC C
[28]
Magn. Magn. Mater. 308 (2007) 325–340.
[29]
D.T.Morelli, A.M.Mance, J.V.Mantese, A.L.Micheli, Magnetocaloric properties of doped lanthanum manganite films, J.Appl.Phys.79(1996) 373–375.
[29]
C.P. Reshmi, S.Savitha Pillai, K.G.Suresh, Manoj Raama Varma, Room temperature magnetocaloric properties of Ni substituted La0.67Sr0.33MnO3, Solid State Sci.19(2013)130–135.
[30]
Y.Sun, W.Tong, Y.H.Zhang, Large magnetic entropy change above 300 K in La0.67Sr0.33Mn0.9Cr0.1O3, J. Magn. Magn. Mater.232 (2001) 205–208.
ACCEPTED MANUSCRIPT V.K. Pecharsky Jr., K.A. Gschneidner, Effect of alloying on the giant magnetocaloric
EP
TE D
M AN U
SC
RI PT
effect of Gd5(Si2Ge2), J. Magn. Magn. Mater.167(1997) L179–L184.
AC C
[31]
ACCEPTED MANUSCRIPT Table 1. Unit-cell, positional and thermal parameters and discrepancy factors after the refinement of the crystal structure from NPD data at RT of La0.67Sr0.22Ba0.11Mn1-xFexO3. Cristallite size is also included. 0
0.1
0.2
0.3
Space group
Pnma
R-3c
R-3c
R-3c
a(Å)
5.4587(6)
5.5152 (2)
5.51264(7)
5.51699(7)
b(Å)
7.7177(12)
-
-
-
c(Å)
5.5271(7)
13.3972(7)
13.4135(2)
13.4216(2)
V(Å3)/Z*
58.21(1)
58.82(1)
58.84(1)
58.96(1)
La/Ba/Sr
4c (x, 1/4 , z)
6a (0, 0, 3/4)
x
0.0020(5)
z
-0.0258(1)
B(Å2)
0.93(8)
Mn/Fe
4b (0, 0, 1/2)
6b (0, 0, 0)
B(Å2)
0.34(9)
0.30
M AN U 0.44(6)
TE D
O1
SC
Cell parameters
RI PT
Fe content (x)
0.55(3)
0.54(3)
0.30
0.30
4c (x, 1/4 , z)
18e (x, 0, 1/4)
0.4989(9)
0.4625(3)
0.4627(1)
0.4644(1)
1.24(4)
1.20(2)
1.10(2)
0.7617(1)
-
-
-
0.02148(5)
-
-
-
0.2485(6)
-
-
-
1.6(2)
-
-
-
Rp
5.59
4.89
2.89
2.77
Rwp
7.96
6.96
3.65
3.46
Rexp
1.84
2.16
1.92
2.21
EP
x
0.0073(1)
z 2
B(Å )
AC C
O2
0.74(9)
x y z 2
B(Å )
8d (x ,y ,z)
Discrepancy factors (%)
ACCEPTED MANUSCRIPT 18.7
10.4
3.63
2.46
RBragg
5.91
5.21
3.08
3.01
Crystallite Size 28.19 32.31 28.8 D(nm) *Z: formula units per unit cell; Z= 4 for Pnma; Z= 6 for R-3c
33.97
Table
2.
Main bond
distances
(Å)
and
RI PT
χ2
selected
Fe content (x)
0
0.1
Bond distances 1.9299(3)
Mn-O2
1.911(2)
Mn-O2
1.989(2)
Angles 177.55(4)
Mn-O2-Mn
169.81(10)
EP AC C
1.9546(6)
(deg)
0.3
1.9569(4)
-
-
-
-
-
-
167.858(10)
167.963(4)
168.478(3)
-
-
TE D
Mn-O1-Mn
1.9555(4)
0.2
M AN U
Mn-O1
SC
La0.67Sr0.22Ba0.11Mn1-xFexO3 at RT.
angles
-
for
ACCEPTED MANUSCRIPT Table 3. Maximum entropy change │∆SMax│ and relative cooling power (RCP), for La0.67Sr0.22Ba0.11MnO3 and La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 compounds, occurring under magnetic field variations, compared to several materials considered for magnetic refrigeration
5 5 5 5 5 5 5 5
EP AC C
(J/KgK) 2.46 2.43 0.91 2.26 1.48 3 5 9.5
Rcp (J/Kg) 169 241 70 153 161 132 200 410
Reference
RI PT
360 268 94 190 292 290 328 293
TE D
La0.67Sr0.22Ba0.11MnO3 La0.67Sr0.22Ba0.11Mn0.9Fe0.1O3 La0.67Sr0.22Ba0.11Mn0.8Fe0.2O3 La0.67Ba0.22Sr0.11Mn0.9Fe0.1O3 La0.67Ba0.33MnO3 La0.67Sr0.33Mn0.9Ni0.1O3 La0.67Sr0.33Mn0.9Ni0.1O3 Gd
µ 0∆H (T)
SC
Tc (K)
M AN U
Sample
This work This work This work [17] [28] [29] [30] [31]
ACCEPTED MANUSCRIPT Figure captions Fig. 1. X-ray diffraction patterns of La0.67Sr0.22Ba0.11Mn1-xFexO3 compounds, Rietveld refined with the model derived from NPD data. a) x= 0, b) x= 0.1, c) x= 0.2, c) x= 0.3.
Fig. 2. Observed (crosses), calculated (full line), and difference (bottom) NPD Rietveld
Bragg positions. a) x= 0, b) x= 0.1, c) x= 0.2, c) x= 0.3.
RI PT
profiles for La0.67Sr0.22Ba0.11Mn1-xFexO3 (0≤x≤0.3) at 298 K. Vertical lines correspond to the
Fig. 3. View of the orthorhombic (Pnma) crystal structure of La0.67Sr0.22Ba0.11MnO3 and the
SC
coordination polyhedron of Mn displaying the Mn-O distances.
M AN U
Fig. 4. View of the rhombohedral (R-3c) crystal structure of La0.67Sr0.22Ba0.11MnO3 and the coordination polyhedron of Mn displaying the equal Mn-O distances.
Fig. 5. (a) Variation of cell unit volume and the average
TE D
0, (b) x=0.1, (c) x=0.2 and (d) x=0.3
Fig. 7. Temperature dependence of ZFC and FC magnetization data taken at H= 1000 Oe for:
EP
(a) x=0, x=0.1; (b) x=0.2, x=0.3; the inset represents dM/dT versus T curves, to determine TC. Fig. 8. Magnetization vs Field isotherms near TC for La0.67Sr0.22Ba0.11Mn1-xFexO3 (x=0, 0.1
AC C
and 0.2) samples
Fig. 9. Arrott plots around TC for La0.67Sr0.22Ba0.11Mn1-xFexO3 (x=0 and 0.1) samples. Fig. 10. Thermal evolution of the entropy under different amplitudes of change in the magnetic
field
(from
bottom
to
top
∆H=1
T,
2T,
3T,
4T,
and
5T)
for
La0.67Sr0.22Ba0.11Mn1-xFexO3. a) x=0, b) x= 0.1 and x=0.2. Fig.11. Relative cooling power values (RCP) versus applied magnetic field for La0.67Sr0.22Ba0.11Mn1-xFexO3 (x = 0, 0.1 and 0.2) compounds.
ACCEPTED MANUSCRIPT
AC C
EP
b
TE D
M AN U
SC
RI PT
a
Fig.1
ACCEPTED MANUSCRIPT
AC C
EP
d
TE D
M AN U
SC
RI PT
c
Fig.1
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
a
AC C
EP
TE D
b
Fig.2
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
c
AC C
EP
TE D
d
Fig.2
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.3
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.4
ACCEPTED MANUSCRIPT
1,960 59,0
a 1,955
RI PT
1,950
1,945
58,6
1,940
1,935
SC
58,4
M AN U
58,2 0,0
0,1
0,2
1,930 0,3
x
TE D
b
171,0
EP
172,5
AC C
174,0
169,5
168,0
0,0
0,1
0,2
X
Fig.5
0,3
3 V (A° )
58,8
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.6
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.6
ACCEPTED MANUSCRIPT 0,4
80
FC (x=0) FC (x=0.1)
a 0,0
dM/dT
70
50
Tc=232K
-0,4
RI PT
-0,8
Tc=360K
40 -1,2 0
30
200
400
20
SC
T (K)
x=0(FC ) x=0(ZFC ) x=0.1(FC ) x=0(ZFC )
10 0 0
100
200
M AN U
M(emu/g)
60
300
400
500
600
700
b
10
EP
x = 0 .2 (Z F C ) x = 0 .2 (F C ) x = 0 .3 (Z F C ) x = 0 .3 (F C )
6
AC C
M(emu/g)
8
TE D
T(K )
4
2
0 0
Fig.7
100
200
T (K )
300
ACCEPTED MANUSCRIPT 50
300K
x=0
30
∆T=8T
RI PT
M(emu/g)
40
20
10
0 0
1
2
3
µ 0 H (T ) x = 0 .1 70 60
M(emu/g)
50 40
5
5K 180K
∆T=8K
TE D
30
4
a
M AN U
80
SC
420K
20 10 0
1
EP
0
2
280K 300K
b 3
4
5
µ 0 H (T )
50K
x = 0 .2
AC C
40
M(emu/g)
30
∆T=8K
20
200K 10
c 0 0
Fig.8
1
2
3
µ 0 H (T )
4
5
ACCEPTED MANUSCRIPT
300K
x=0
RI PT
2000
2
-2
M (emu g )
1500
1000
500
0 0,00
0,08
0,16
M AN U
2
SC
∆ T=8K
0,24
0,32
30 0 0
x = 0 .1 25 0 0
g)
∆ T= 8 K
10 0 0
280K
500
0 0 ,00
0 ,0 4
b 0 ,0 8
0,1 2
0 ,1 6
µ 0 H /M (T e m u
Fig.9
0,48
180K
EP
15 0 0
0,40
AC C
2
2
-2
M (emu g )
20 0 0
-1
a
TE D
µ 0 H /M (T em u
420K
0 ,2 0 -1
g)
0 ,2 4
0 ,2 8
ACCEPTED MANUSCRIPT 1T 2T 3T 4T 5T
a
2 ,4
1 ,6
1 ,2
M
-∆ S (J/Kg.K)
2 ,0
0 ,4
0 ,0 300
320
340
360
380
2 ,4
b
M AN U
2 ,0
1 ,6
1 ,2
M
-∆ S (J/Kg.K)
400
SC
T (K )
RI PT
0 ,8
0 ,8
0 ,0 180
200
220
240
260
280
c
M
-∆S (J/Kg.K)
300
1T 2T 3T 4T 5T
AC C
0 ,8
1T 2T 3T 4T 5T
T (K )
EP
1 ,0
TE D
0 ,4
420
0 ,6
0 ,4
0 ,2
0 ,0 40
60
80
100
120
T (K )
Fig.10
140
160
180
200
250
M AN U
SC
x=0 x=0.1 x=0.2
200
Rcp (J/Kg)
RI PT
ACCEPTED MANUSCRIPT
150
100
0
2
AC C
EP
1
TE D
50
Fig.11
3
µ0H (T)
4
5
ACCEPTED MANUSCRIPT HIGHLIGHTS
-Novel Fe-doped manganite oxides prepared by a sol-gel procedure
- Ferromagnetic behavior for x= 0, 0.1; spin glass for x= 0.2, 0.3
RI PT
- Neutron diffraction shows a phase transition upon Fe introduction, since tolerance factor increases
AC C
EP
TE D
M AN U
SC
- Magnetocaloric effect enhanced for x=0.1; improved “relative cooling power” respect x=0