Study on the influence of magnetic phase transitions on the magnetocaloric effect in Sm0.7Sr0.3Mn0.95Fe0.05O3 manganite

Accepted Manuscript Study on the influence of magnetic phase transitions on the magnetocaloric effect in Sm0.7Sr0.3Mn0.95Fe0.05O3 manganite E.K. Abdel-Khalek, A.F. Salem, E.A. Mohamed PII: DOI: Reference:

S0925-8388(14)00905-0 http://dx.doi.org/10.1016/j.jallcom.2014.04.092 JALCOM 31057

To appear in: Received Date: Revised Date: Accepted Date:

3 March 2014 14 April 2014 15 April 2014

Please cite this article as: E.K. Abdel-Khalek, A.F. Salem, E.A. Mohamed, Study on the influence of magnetic phase transitions on the magnetocaloric effect in Sm0.7Sr0.3Mn0.95Fe0.05O3 manganite, (2014), doi: http://dx.doi.org/ 10.1016/j.jallcom.2014.04.092

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Study on the influence of magnetic phase transitions on the magnetocaloric effect in Sm0.7Sr0.3Mn0.95Fe0.05O3 manganite E. K. Abdel-Khaleka, A. F. Salemb and E.A. Mohamedc a

Department of Physics, Faculty of Science, Al Azhar University, Nasr City 11884, Cairo, Egypt.

b

Department of Physics, King Fahd University of Petroleum& Minerals, Dhahran 31261, KSA.

c

Department of Physics, Faculty of Science (Girl’s Branch), Al Azhar University, Nasr City, Cairo, Egypt

Abstract In this work, the structural, magnetic, magnetocaloric effect (MCE) and refrigerant capacity (RC) properties of nanosize Sm 0.7Sr0.3Mn0.95Fe0.05O3 manganite have been investigated. Structural characterization shows that this sample has orthorhombic (Pbnm) phase with the small impurities (Mn3O4). The sample undergoes second order paramagnetic to ferromagnetic transition at TC=90 K followed by two types of magnetic states at T < TC, which is formed by the presence of second order charge ordered at TCO=28 and first order antiferromagnetic clusters at TN=18 K. The magnetic entropy change ∆Sm changes from negative around TC to positive around TCO and TN indicating the presence of normal and inverse MCEs. The influence of first and second order magnetic phase transitions on the MCE and RC are reported. Keywords: Nanosize manganite; Magnetization; Magnetocaloric effect; refrigerant capacity. *Corresponding author. Tel.: E-mail addresses: [email protected]

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1. Introduction Recently, Sm1-xSrxMnO3 system has unique magnetic and magnetocaloric properties owing to the presence of multiphase competition among the ferromagnetic metallic (FM) state and charge-orbital-ordered (CO/OO) states with the collectively Jahn–Teller distortion [1-4]. The unique magnetic and magnetocaloric properties of this system depend on several factors such as the ionic radii of the metal ions, (There are large difference between the ionic radii of Sm and Sr), the percentage of the Sr ions, and the method used in the preparation of the system, etc [1-4]. The phase diagram of the Sm1xSrxMnO3

for ceramic [5] and single-crystal shows three different phases. Ferromagnetic

metallic (FMM) in the range 0.3 ≤ x ≤ 0.48, an orbitally ordered (OO) or charge-ordered (CO) insulator at x=0.49 and 0.50, and an antiferromagnetic insulating (AFMI) in the range 0.51 ≤ x ≤ 0.6 [2, 3]. The two phases FMM and CO/OO insulator are observed together only at x=0.49 and x=0.5. The competition between the FMM, CO/OO, and AFMI phases becomes dominant near x=0.5 for single crystal [2, 3]. C. Martin et al. and V. V. Runov et al. [5, 6] applied neutron diffraction and electron diffraction on the Sm 1−xSrxMnO3 system and showed that a magnetic inhomogeneous state for x=0.4, 0.45 consisting of FM clusters, A-type-AFM clusters and CO-AFM clusters [5-7]. Based on magnetic and magnetocaloric properties studies in Sm1−xSrxMnO3 (x=0.3–0.5), A. Rebello and R. Mahendiran [8] suggested that x=0.3 composition shows a magnetic second order transition and first order transition at x=0.3 and 0.5 in the paramagnetic state.

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Furthermore, the x=0.4 composition shows the highest magnetocaloric effect (MCE). Based on magnetic, and magnetocaloric properties studies in Sm0.7‒xLaxSr0.3MnO3 (0 ≤ x ≤ 0.7), M. Aparnadevi and R. Mahendiran [9] suggested that all the compounds show second order paramagnetic to FM transition at TC, (83 K ≤ TC ≤ 373 K). The insulating ferromagnet at x=0 transforms to a ferromagnetic metal for x=0.1 below TC. The fieldcooled M(T) of all except x=0.7 compounds show a cusp at a temperature T* much below Tc. The authors also suggested that the decrease of M(T) below T* is due to ferrimagnetic interaction between Mn and Sm sublattices [9]. V. Dyakonov et al. [10] have employed a co-precipitation method at different temperatures to obtain nanosize La0.7Sr0.3MnO3. They found that all the nanosize manganites show ferromagnetic like ordering and smaller magnetic entropy change. In addition to the doping with Fe in manganites lead to the formation of magnetic clusters with different size, random canting of spins or spin glass like behavior, superparamagnetic clusters, etc. [11, 12]. Furthermore, it is known that a small amount of Fe ions in the manganites occupy high-spin Fe3+ state and coupled antiferromagnetically with Mn ions [13-15]. In view of the aforementioned aspects, Sm0.7Sr0.3Mn0.95Fe0.05O3 sample has been synthesized by the co-precipitation method. The structural, magnetic, MCE and RC properties of the present sample have been studied. 2. Experimental

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Polycrystalline sample of the composition Sm0.7Sr0.3Mn0.95Fe0.05O3 was prepared by co-precipitation method using ammonium carbonate [12-15]. Powder x-ray diffraction (XRD) pattern of the sample at room temperature (RT) was obtained from SIEMENS D5000 diffractometer with Cu-Kα radiation. The analysis of such XRD pattern was carried out by the FULLPROF program based on the Rietveld method [12-15]. The crystallite size was estimated using the Scherrer's equation [16]; L = kλ/(βcosθ) where L is the crystallite size, k is a constant approximately equal to unity, λ is the wavelength used (1.5406 Å), β is the full-width at half-maximum in radians (obtained for high intense peak in the present studies) and θ is the related Bragg angle. Magnetization measurements were performed on a 9-Tesla PAR-4500 vibrating sample magnetometer (VSM) in the temperature range from 4.2 to 248 K. Temperature dependent magnetization was performed under a constant magnetic field of 0.099T. The magnetic moment was calibrated using a standard Ni sample and the temperature was monitored using a calibrated carbon-glass resistor [15]. 3. Results and discussion 3.1. Powder x-ray diffraction (XRD) The XRD pattern for the polycrystalline Sm 0.7Sr0.3Mn0.95Fe0.05O3 sample (Fig. 1) shows its single-phase character with the presence of a small amount of Mn3O4 [13, 17]. Rietveld refinement of the data (Fig. 1) reveals that the sample crystallizes in orthorhombic distorted perovskite structure with space group Pbnm which is consistent

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with the previous results [13-15]. In the orthorhombic structure, oxygen ions occupy two nonequivalent sites, namely OI (4c) and OII (8d), with a population ratio of 1:2. Six O2− ions (two OI and four OII) surround each Mn and Fe ions and form an octahedron [13]. The refined structural parameters including the lattice parameters, positional parameters, unit cell volume, bond lengths and bond angles are summarized for the sample in Table 1. The crystal structure for Sm0.7Sr0.3Mn0.95Fe0.05O3 sample which based on the refined atomic positions was represented graphically as shown in Fig.2. From this figure it can seen that the sample consist of MnO6 octahedra residing in the lattice formed by Sm and Sr. From table 1 it can be seen that the orthorhombic phase has a ratio c/a < √2 and there is one long Mn-O bond and two short ones in MnO6 octahedral, which reveal the presence of the Jahn-Teller distortion [13-15]. The crystal size (L=45 nm) was calculated from X-ray spectrum by Scherrer's equation indicating the sample being nanosized. 3.2. Magnetic measurements The temperature dependence of zero-field cooled (ZFC) magnetization for Sm0.7Sr0.3Mn0.95Fe0.05O3 under a magnetic field of 0.099 T and in the temperature range from 4.2 to 248 K, is depicted in Fig. 3. From this Figure, it can be seen that the ZFC magnetization curve increases with decreasing temperature below TC. Further, the ZFC magnetization shows an anomalous broad peak as we lower the temperature and then drops sharply below this peak. Such a peak was also observed in previous studies by other researchers [9,18, 19]. The sharp decrease of ZFC magnetization M(T) below a broad peak,

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which is a signature of cluster freezing [20], can be attributed to the antiparallel coupling of 3d spins of Mn sublattice and 4f spins of Sm sublattice [9, 18]. In a study reported by V. B. Naik and R. Mahendiran [18], they suggested that although these sublattices themselves order ferromagnetically, exchange coupling between them can be antiferromagnetic. In addition to the ordering of Sm3+(4f5) moment should have been induced by the molecular field of the Mn sublattice [18]. The magnetic transition temperatures have been determined from the minimum and two maxima in the first derivative of dM/dT vs. T curve [15, 21], as shown in Fig. 4. From this Figure, it is found that there are three magnetic transitions in Sm0.7Sr0.3Mn0.95Fe0.05O3 paramagnetic to ferromagnetic transition at TC=90 K and two types of magnetic states at T < TC is like to cluster glass, which is formed by the presence of charge ordered at TCO=28 and antiferromagnetic clusters at TN=18 K in the ferromagnetic matrix [20]. M. K. Srivastava et al. [20] suggested that the interpretation of TN due to the formation of "antiferromagnetic clusters" in thin films of Sm 0.53Sr0.47MnO3. This is not adequate where we are not in the presence of thin films and a region of the phase diagram far away of the studied compound. V. Runov et al and A. I. Shames et al. [22, 23] studied the Sm1−x SrxMnO3 using neutron and electron diffraction. They found that the existence of nanometer-scale CO/AFM clusters near the Curie temperature. N. S. Bingham et al. [24] found that a remarkable change in magnetization at 30 K is observed in the Sm 1−xSrxMnO3, which is related to the onset of the antiferromagnetic order and/or spin reorientation of the

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spontaneous magnetization [24]. S. T. Mahmud et al. [11] studied the polycrystalline Sm0.60Sr0.40Mn1−xFexO3 (0≤x≤0.02). They suggest that the strong suppression of the FMM phase by the Fe doping in Sm1−xSrxMnO3 evolves this inherent CO/OO instability. Biswas et al. [25] studied the Pr0.65(Ca0.6Sr0.4)0.35MnO3 nanocrystalline and concluded that the coexistence of CO and FM phase at low magnetic field. By comparing the above results with the present study, we found three magnetic transitions at TC=90, TCO=28 and TN=18 K in the ZFC curve at low and fixed applied field which may be attributed to the magnetic inhomogeneity due to Fe in manganites, the impurity phase and nanocrystalline form of the sample (L=45 nm) [26]. Fig. 5 shows the isotherms of magnetization M(H) curves measured around magnetic phase transitions. It can be seen that the hysteretic losses (the area is composed of the increasing and decreasing field curves [27]) are very large below the TCO, whereas they are small at T=50 K and negligible below the TC at T=75 K and increases above TC at T=100 K. The isotherm of magnetization M(H) curve becomes linear at T =150 K (inset Fig. 5) which indicated the occurrence of paramagnetic phase due to thermal energy. The difference in the width of the hysteresis in M(H) with increasing T may be attributed to the different nature of magnetic phase transition [28]. Fig. 6 shows the magnetization (M) isotherms around the three magnetic transition temperatures and Fig. 7 shows H/M versus M2 for the present sample. We have taken magnetization isotherms at a temperature interval of ∆T=21 K between 4 and 25 K, ∆T=25 K between 25 and 100 K and ∆T=50 K between 100 and 150 K. The field dependence of the

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magnetization becomes linear at T =150 K (inset Fig. 6) due to the magnetization in the paramagnetic state [18]. According to Banerjee criterion, the magnetic transition is of second order if the H/M vs. M2 curves have a positive slope [29]. On the other hand, if some of the H/M vs. M2 curves show a negative slope at some point, the transition is of first order [30, 31]. It can be observed in Fig. 7 that the change in the slope of the curves from positive around TC, and around TCO to negative at T < TN (at low H/M vs. M2 for T = 4 K). To calculate the change in magnetic entropy (∆SM) we used the isothermal magnetization measurements at discrete field intervals (Fig. 6) and initial magnetization curve (Fig. 3) for narrow temperature range. The ∆SM(T, H) was calculated by the Maxwell relation [32].

∆S M (T , H ) =

Hm

 ∂M 

∫  ∂T  0

dH H

where M is the magnetization, we have found the derivative ∂M / ∂T , and substituted it in the above equation [9, 18, 29]. Fig. 8 shows the temperature dependence of the change in magnetic entropy (-∆SM) taken at different magnetic fields ranging from 0.5 to 5 T. From Fig. 8 it can be seen that the ∆SM values of present sample exhibit a broad negative peak around the TC (i.e. normal MCE) and ∆Sm values are positive around the TCO and TN at low field (i.e. inverse MCE) [9, 18]. The normal MCE arises from ferromagnetic exchange interaction between Mn spins. In a recent study reported by V. B. Naik and R. Mahendiran [18] the normal MCE arises from ferromagnetic exchange interaction between Mn spins

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while the inverse MCE arises from antiferromagnetic superexchange interaction between Mn and Sm. In addition to also arises from a spin-reorientation transition occurs in the Mn-spin lattice. Our experimental study leads to a similar expectation. To verify the nature of the inverse MCE we calculated the change in magnetic entropy in narrow temperature range from magnetization curve (Fig. 3). In addition to the large change in magnetic entropy occurs at a low and fixed applied magnetic field which makes this material useful for magnetic refrigeration [8, 33]. Fig. 9 shows the temperature dependence of the change in magnetic entropy (-∆SM) taken at 0.099 T. From Fig. 9 it can be seen that the ∆SM values at TN and TCO (0.225 and 0.028J /kg K respectively) is much larger than that at TC (- 0.043 J /kg K) thus ∆SM in a second order transition is smaller than that in the first-order transition [9]. The lower magnitude of ∆SM in present sample can result from an almost negligible contribution from the magnetically disordered nanosize manganites [10]. Damay et al. [34] studied the magnetization versus temperature at 1.4 T for Sm0.7Sr0.3Mn1−xFexO3 ( 0 < x ≤ 0.10) and concluded that the ferromagnetic character of the samples at low temperature for 0 < x ≤ 0.03 these compounds exhibit ferromagnetic to paramagnetic transition. For higher x values the ferromagnetism vanishes rapidly, as shown for x = 0.04 and 0.05. The magnetocaloric effect for Fe doped manganite (Sm0.7Sr0.3Mn0.95Fe0.05O3 ) is much smaller than the effect in the non-doped compounds where the introducing of Fe increases magnetic inhomogeneity and leads to broadens the

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ferromagnetic transition and hence decreases ∆SM [9, 35]. We compute refrigerant capacity (RC) around the TC, TCO and TN using the following equation [9, 27], T2

RC = − ∫ ∆S M (T )dT T1

where T1 and T2 are the temperatures corresponding to the half-maximum of the ∆SM (T) peak around TC, TCO and TN. Fig. 9 shows the method for calculating the RC from the area under the –∆SM(T) curve in each temperature range around TC, TCO and TN. The first-order magnetic transition at TN and second order magnetic transition at TCO induces small RC (0.829 J/kg and 0.266 J/kg respectively) while the second order magnetic transition at TC induces large RC (0.954 J/kg). By comparing the values of RC and –∆SM around TC, TCO and TN it is found that the RC does not depend only on the magnitude of –∆SM, but also on the T1 and T2 which are the temperatures corresponding to the half-maximum of the ∆SM [27]. The smaller values of RC comparison to the literature data due to the presence of Fe which leads to increase the disorder in the sample which results in an inhomogeneous sample and smaller values of magnetocaloric effect. In addition to the smaller values of RC may be result from an negligible contribution from the magnetically disordered nanosize [35]. The value of RC around the TC indicates that the magnetic refrigeration in the vicinity of the TC is more effective than that around the TN and TCO [27]. 4. Conclusions

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In summary, the nanosize Sm0.7Sr0.3Mn0.95Fe0.05O3 manganite crystallizes in orthorhombic structure and exhibits both normal and inverse magnetocaloric effects. The sample undergoes a second order magnetic transition from the paramagnetic to the ferromagnetic at TC= 90 K followed by a second order from the ferromagnetic to charge ordered at TCO=28 K and a first order magnetic transition from charge ordered to antiferromagnetic at TN=18 K. The influence of first and second order magnetic phase transitions on RC show that the large value of RC around the TC indicates that magnetic refrigeration in the vicinity of the TC is more effective than that around the TN and TCO. Acknowledgement A. F. Salem would like to acknowledge the support of King Fahd University of Petroleum & Minerals. References [1] A. I. Kurbakov, C. Martin and A. Maignan, J. Magn. Magn. Mater. 321 (2009) 2601. [2] Y. Tomioka, H. Hiraka,Y. Endoh and Y. Tokura, Phys. Rev. B 74 (2006) 104420. [3] A. I. Kurbakov, A. V. Lazuta and V. A. Ryzhov, Journal of Physics: Conference Series 200 (2010) 012099. [4] R. Choithrani, N K Gaur and R K Singh, J. Phys.: Condens. Matter 20 (2008) 415201.

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[5] C. Martin, A. Maignan, M. Hervieu and B. Raveau, Phys. Rev. B 60 (1999) 12191. [6] V. V. Runov, D. Yu. Chernyshev, A. I. Kurbakov, M. K. Runova, V. A. Trunov and A. I. Okorokov, JETP (2000)1181174. [7] A. I. Abramovich, L. I. Koroleva and A. V. Michurin, J. Phys.: Condens. Matter 14 (2002) L537. [8] A. Rebello and R. Mahendiran, Appl. Phys. Lett. 93 (2008) 232501. [9] M. Aparnadevi and R. Mahendiran, J. Appl. Phys.113 (2013) 013911. [10]V. Dyakonov, A. Slawska-Waniewska, N. Nedelko, E. Zubov, V. Mikhaylov, K. Piotrowski, A. Szytua, S. Baran, W. Bazela, Z. Kravchenko, P. Aleshkevich, A. Pashchenko, K. Dyakonov, V. Varyukhin and H. Szymczak, J. Magn. Magn. Mater. 322 (2010) 3072. [11]S. T. Mahmud, M. M. Saber, H. S. Alagoz, K. Biggart, R. Bouveyron, Mahmud Khan, J. Jung, and K. H. Chow, Appl. Phys. Lett. 100 (2012) 232406. [12]A. G. Mostafa, E. K. Abdel-Khalek, W. M. Daoush, M.Y. Hassaan, Hyperfine Interact. 184 (2008) 167. [13] A.G. Mostafa, E.K. Abdel-Khalek, W.M. Daoush, S.F. Moustfa, J. Magn. Magn. Mater. 320 (2008) 3356.

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[14] E. K. Abdel-Khalek, W. M. EL-Meligy, E. A. Mohamed, T. Z. Amer, H. A. Sallam, J. Phys. Condens. Matter 21 (2009) 026003. [15] E. K. Abdel-Khalek, A. F. Salem, E. A. Mohamed, A. A. Bahgat, J. Magn. Magn. Mater. 322 (2010) 909. [16] P. Scherrer, Nachr. Ges. Wiss. Göttingen 26 (1918) 98. [17]P. A. Joy, C. R. Sankar, S. K. Date, J. Phys.: Condens. Matter 14 (2002) L663. [18] V. B. Naik and R. Mahendiran, J. Appl. Phys.110 (2011) 053915. [19] E. M. Levin and P. M. Shand, J. Magn. Magn. Mater. 311 (2007) 675. [20] M. K. Srivastava, M. P. Singh, P. K. Siwach, A. Kaur, F. S. Razavi, H. K. Singh, Solid State Commun. 152 (2012) 138. [21] S. Asthana, D. Bahadur, A. K. Nigam and S. K. Malik, J. Phys.: Condens. Matter 16 (2004) 5297. [22]V. Runov, H. Glattli, G. Kopitsa, A. Okorokov, and M. Runova, Physica B 276, (2000)795. [23]A. I. Shames, A. Yakubovsky, V. Amelichev, O. Gorbenko, and A. Kaul, Solid State Commun. 121 (2002)103.

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[24]N. S. Bingham, P. J. Lampen, The-Long Phan, Manh-Huong Phan, Seong-Cho Yu and H. Srikanth, J. Appl. Phys. 111 (2012) 07D705. [25]A. Biswas, T. Samanta, S. Banerjee and I. Das, , Appl. Phys. Lett. 92 (2008) 012502. [26]Z.H. Wang, D.Y. Geng, Y.J. Zhang and Z.D. Zhang, J. Crystal Growth 310 (2008) 4148. [27]N. S. Bingham, M. H. Phan, H. Srikanth, M. A. Torija and C. Leighton, J. Appl. Phys. 106 (2009) 023909. [28]P. Sarkar, P. Mandal, A. K. Bera, S. M. Yusuf, L. S. Sharath Chandra and V. Ganesan, Phys. Rev. B 78 (2008) 012415. [29]S. K. Banerjee, Phys. Lett. A12 (1964) 16. [30] J. Mira, J. Rivas, F. Rivadulla, C. Vazquez and M. A. Lopez-Quintela, Phys. Rev. B 60 (1999) 2998. [31]M. H. Phan, V. Franco, N. S. Bingham, H. Srikanth, N. H. Hur and S.C. Yu, J. Alloy. Compd. 508 (2010) 238. [32]A. H. Morrish, The Physical Principles of Magnetism IEEE, New York, (2001). [33]P. Sarkar, P. Mandal and P. Choudhury, Appl. Phys. Lett. 92 (2008) 182506. [34]F. Damay, A. Maignan, N. Nguyen, B. Raveau, J. Solid State Chem. 124 (1996) 385.

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[35] S. K. Barik, C. Krishnamoorthi and R. Mahendiran, J. Magn. Magn. Mater. 323 (2011) 1015.

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Table 1 Structural parameters for Sm0.7Sr0.3Mn0.95Fe0.05O3 perovskite sample obtained from the structural refinement using X-ray powder diffraction data at room temperature

Mn-O-Mn (°)

Lattice coordinate Lattice parameters

Atom

Site

x

y

z

-3

± 3×10 (A˚)

Mn-O(Ǻ)

Crystal Size

Mn-OI-Mn Mn-OII-Mn Mn-OI Mn-OII L(nm) ± 0.5˚

5×10

-3

± 3.0 (nm)

Orthorhombic (Pbnm) a= 5.4249 Mn 3+, Fe 3+ and Mn4+ 4a 0.000 0.000 0.000 b= 5.4716

Sm3+ and Sr2+

c= 7.6103

O2-I

4c 0.695 0.559

O2- I I

8d -0.232 -0.249 0.980

V= 225.894 ± 10-2 (Å3)

4c 0.501 -0.016 0.250 0.250

131.90

160.01

2.087

2.231 45 1.675

Figure Captions: Fig. 1 Rietveld plot of XRD pattern for the studied sample. Red dots indicate the experimental data and the black lines overlapping them indicate calculated profiles. The lowest curve shows the difference between experimental and calculated patterns. The vertical bars in green are the expected Bragg’s positions. The peak with star is attributed to the Mn3O4. Fig. 2 The crystal structure for Sm0.7Sr0.3Mn0.95Fe0.05O3 sample based on the refined atomic

positions of the orthorhombic Pbnm phase. Fig. 3 Temperature dependence of ZFC magnetizations taken at a field of 0.099 T for the studied sample. Fig. 4 The derivative of magnetization with respect to temperature (dM/dT vs T). Fig. 5 Hysteresis in M(H) at different fixed temperatures around three magnetic phase

transitions for the studied sample. Fig. 6 Isothermal magnetization curves taken at different fixed temperatures around three

magnetic phase transitions for the studied sample. Fig. 7 Magnetization isotherms replotted as H/M vs M2 at different fixed temperatures around three magnetic phase transitions for the studied sample. Fig. 8 Temperature dependence of magnetic entropy change (−∆SM) at different applied

fields up to 5 T for the studied sample. Fig. 9 The method for calculating the RC from the −∆SM (T) curve.

1

2

Fig. (1)

Mn/Fe Sm/Sr OI OII

Fig. (2)

3

18 16 14

10 8 6 4 2 0 -2 0

50

100

150

200

250

T(K)

Fig. (3) 2.5 TN

-1

dM/dT (emu.g .K )

2.0

-1

M (emu/g)

12

B

1.5 1.0 0.5

TCO

0.0 -0.5

TC

-1.0 0

50

100

150

T(K)

Fig. (4)

200

250

4

50

4 K 25 K 50 K 75 K 100 K

30 14

20

150 K

12

M(emu/g)

M(emu/g)

40

10

10 8 6 4 2 0 0

0 0

20000

10000 20000 30000 40000 50000 H(Oe)

40000

60000

80000

H(Oe)

Fig. (5) 50 4K 25 K 50 K 75 K 100 K

30 14 150 K

12

20

10 8

M(emu/g)

M(emu/g)

40

6

10

4 2 0 0

10000

20000

30000

40000

50000

H(Oe)

0 0

20000

40000

60000

H(Oe)

Fig. (6)

80000

100000

5

3000

4K 25 K 50 K 75 K 100 K

H/M (Oe.g/emu)

2500 2000 1500 1000 500 0 0

500

1000 1500 2 2 M (emu/g)

2000

Fig. (7) 0.5 T 1.0 T 1.5 T 2.0 T 2.5 T 3.0 T 3.5 T 4.0 T 4.5 T 5.0 T

0.15

0.05

-1

-1

-  SM(J kg K )

0.10

0.00 -0.05 -0.10 -0.15 0

25

50

75

100 125 T (K)

Fig. (8)

150

175

200

6

0.10 0.099 T RC at Tc

0.05

TFWHM

T1

T2

-1

-1

-  SM(J kg K )

0.00 RC at TCO

-0.05 -0.10 -0.15 -0.20 -0.25

RC at TN

0

50

100 T (K)

Fig. (9)

150

200

250

17 Highlights ► The nanosize Sm0.7Sr0.3Mn0.95Fe0.05O3 manganite was synthesized. ► The sample exhibits both normal and inverse magnetocaloric effects (MCE). ► The influence of first and second order magnetic phase transitions on the MCE and refrigerant capacity (RC) are reported.