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Magnetocaloric effect in In doped YbMnO3
Author’s Accepted Manuscript Magnetocaloric effect in In doped YbMnO3 Bhumireddi Sattibabu, A.K. Bhatnagar, K. Vinod, Awadhesh Mani
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To appear in: Physica B: Physics of Condensed Matter Received date: 10 January 2017 Revised date: 15 March 2017 Accepted date: 16 March 2017 Cite this article as: Bhumireddi Sattibabu, A.K. Bhatnagar, K. Vinod and Awadhesh Mani, Magnetocaloric effect in In doped YbMnO 3, Physica B: Physics of Condensed Matter, http://dx.doi.org/10.1016/j.physb.2017.03.024 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 galley proof before it is published in its final citable 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.
Magnetocaloric effect in In doped YbMnO3 Bhumireddi Sattibabu1,2*, A. K. Bhatnagar3, , K. Vinod4, Awadhesh Mani4 1
School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India
2
Department of Electronics and Physics, Institute of Science, GITAM University, Visakhapatnam 530045, India 3
4
School of Physics, University of Hyderabad, Hyderabad 500046, India
Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam - 603102, India
[email protected] [email protected] *
Corresponding authors: Dr. B. Sattibabu School of Engineering Sciences and Technology,
University of Hyderabad – 500046 INDIA Tel.: +91-40-23134301 / 23013200, Fax: +91-4023010227
Abstract Magnetic and magnetocaloric (MCE) properties of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 polycrystalline samples are presented in this paper. Isothermal magnetization measurements reveal a field induced magnetic transition. Magnetic entropy change of 2.34 ± 0.35 J/mole-K for Yb0.9In0.1MnO3 and 2.64 ± 0.38 J/mole-K for Yb0.8In0.2MnO3 field change ΔH = 10 KOe is observed around the ferromagnetic ordering temperature of Yb3+. Values of relative cooling power for the same field change are found to be 38.03 ± 9 J /mol, and 40.90 ± 10 J/mol for
1
Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3, respectively. These values suggest In doped YbMnO3 may be a potential candidate for magnetic refrigerant at low temperatures. Keywords Magnetic materials; Ceramics; Thermal properties; Magnetic entropy
1. Introduction Magnetocaloric refrigeration systems of much research interest in recent times. Magnetocaloric materials are generally characterized by the parameters like maximum magnetic entropy change (ΔSMax), Relative Cooling Power (RCP) and adiabatic temperature change (ΔTad). Many magnetic materials such as Gd5(Si2-xGe2+x) [1], LaFe13-xSix [2], MnFeP1-xAsx [3] and rare earth manganites [4] etc have been reported to have large magnetic entropy change under an applied magnetic field near magnetic phase transitions. Magnetocaloric properties of multiferroic rare earth manganites are worth investigating [5] and there are several works which have reported magnetocaloric properties of multiferroic rare earth manganites [6,7]. Systems showing large MCE in the low-temperature region from about 10 K down to sub-Kelvin are important for basic research as well as for specific technological applications such as space science and liquefaction of hydrogen in fuel industry. In our previous paper Yb1-xHoxMnO3 (x = 0.1, 0.2 and 0.3) large MCE properties were observed which were interpreted due to the higher magnetic moment of Ho3+ in these compounds [8]. Thus, in order to clarify the factors affecting the magnetocaloric properties of the multiferroic YbMnO3 and related materials, it is of important to study doped YbMnO3 systems with nonmagnetic substitutions as well. InMnO3, has a similar hexagonal structure as that of YbMnO3. The size of In3+ ion (0.925 Å) is only slightly smaller than Yb3+ ion size (0.985 Å), The field 2
induced magnetic transition observed in Yb1-xInxMnO3 has motivated us to investigate the magnetocaloric behavior in this system. Particularly, we are interested in studying the nature of the magnetic entropy change ΔSM and relative cooling power (RCP) in this compound at the Yb3+ ordering transition which takes place at a low temperature. In this work magnetocaloric properties of In doped polycrystalline YbMnO3 samples presented using magnetization measurements. 2. Experimental Details Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples were synthesized by solid state reaction method following a similar procedure as described in ref 9. The samples were characterized by powder x-ray diffraction (XRD) with Cu-Kα radiation (using Bruker D8 Advance X-ray powder diffractometer) and by magnetization measurements (using a commercial vibrating sample magnetometer (VSM): Cryogenic Inc. (UK)). 3. Results and Discussions Figure 1 shows XRD data of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3compounds. No impurity phase is detected and the XRD pattern is indexed using the hexagonal P63cm space group [10]. Lattice parameter values are a ~ 0.601 ± 0.002 nm c ~ 1.135 ± 0.005 nm for Yb0.9In0.1MnO3 and a ~ 0.603 ± 0.002 nm c ~ 1.136 ± 0.004 nm for Yb0.8In0.2MnO3 compounds. The doped lattice parameter is slightly lower than that of undoped one which may be due to small size of In 3+ ion compared to the Yb3+ ion size [10]. Among the Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples the lattice parameters do not vary significantly. This may be due to the fact that the actual In content may be slightly different from the expected/nominal levels or lattice strains.
3
Fig 1. XRD pattern for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 collected at room temperature.
Fig 2 shows temperature (T) dependence of zero field cooled (ZFC) magnetic susceptibility () and its inverse (1/) for the Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 compounds. Data clearly show two magnetic transitions ; first around the Neel temperature (TN) ~ 89 K corresponding to the AFM ordering of the Mn3+ moments and second around the Curie temperatures (TC) ~ 3.8 K corresponding to the ferromagnetic (FM) ordering of Yb3+ moments. Both magnetic transitions are well established and documented for pure and doped YbMnO3 in the literature [9,10]. Two transitions are shown for Yb0.8In0.2MnO3 sample in the zoomed plots given as insets of figure 2. The left inset shows first derivative of vs T around the Yb3+ ordering temperature and the right inset shows first derivative of 1/ vs T around the Mn3+ ordering temperature. The value of Neel temperature (TN) is 89 ± 1 K which is slightly higher than reported for polycrystalline YbMnO3
4
at 85 ± 1 K[10], and is due to the slight reduction in lattice parameter; which reduces the Mn-O bond lengths and strengthen the exchange interactions and therefore for the increase the TN [9]. 1/ vs T data shows linear Curie–Weiss (CW) behavior for T >> TN. Curie temperature (θcw) and effective magnetic moment (μeff) extracted from the Curie-Weiss fit are θcw = -156.7 ± 1.1 K, μeff = 6.02 ± 0.02 µB for Yb0.9In0.1MnO3 and θcw = -160.4 ± 1.5 K and μeff = 6.28 ± 0.02 µB for Yb0.8In0.2MnO3.The negative value of θcw obtained by fitting data points only above TN indicates presence of antiferromagnetic interaction.
Fig.2 Temperature dependence of χ and 1/χ with Curie–Weiss fit of Yb0.9In0.1MnO3 (filled red symbols) and Yb0.8In0.2MnO3 (open black symbols). Upper inset: of Yb3+and lower inset:
( )
of T near the FM transition
of curves of T near the AFM transition of Mn3+ for Yb0.8In0.2MnO3.
5
Fig. 3a shows isothermal magnetization (M-H) curves for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples, respectively, measured under applied magnetic field ranging from 0 to 100 kOe and between 2.5–38 K. A sudden slope change of M vs H at magnetic field ~ 30 kOe is observed and is due to the field-induced magnetic transition. A similar behavior has been observed in some other doped YbMnO3 samples [8]. Fig 3b shows the corresponding Arrott plots (H/M vs M2) for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples, respectively. Both samples exhibit a second order field induced magnetic transition as the Arrots plots have positive slope [11].
2
Fig 3. (a) Field dependence of isothermal magnetization and (b) Arrott plots of H/M vs M at
various temperatures for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3.
6
To obtain the magnetocaloric properties of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples, total magnetic entropy change ΔSM is calculated using Maxwell equations given below [12]: (
)
(
)
∫
(
)
(1)
which is approximated to ∑
(2)
Fig 4 Variation of magnetic entropy change (ΔSM) with temperature for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3.Inset figure shows RCP as a function of field.
7
Figure 4 shows variation in magnetic-entropy change (ΔSM) as a function of temperature for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 at ΔH = 2, 4, 6, 8, and 10 kOe. As seen from Fig. 4, the maximum magnetic entropy change ΔSMax increases with increasing field change. Position of the ΔSMax shifts from 4.5 to 7.5 K as ΔH increases from 2 to 10 kOe. The ΔSMax value is 2.34 ± 0.35 J/mole-K for Yb0.9In0.1MnO3 and is 2.64 ± 0.38 J/mole-K for Yb0.8In0.2MnO3 at a field change of ΔH= 100 kOe. The field induced transition contributes to increase of ΔSMax. The relative cooling power (RCP) of the samples calculated as, RCP S Max TFWHM and RCP values are 38.03 ± 9 J /mol for Yb0.9In0.1MnO3 and 40.90 ± 10 J/mol for Yb0.8In0.2MnO3 with ΔH = 100 kOe. RCP increases with increasing field change as shown inset in the fig 4. ΔSMax and RCP values of the present materials are higher than reported for a single crystal YbMnO3 [13] and comparable to reported perovskite manganites listed in Table 1.
Table.1. Maximum entropy change and RCP of Yb1- xInxMnO3 (x = 0.1 and 0.2) samples Compared with reported values.
Composition
TPeak (K)
ΔH (kOe)
ΔSMmax (J mol-1K-1) If units are 8
RCP (J mol-1) If units are
References
Yb0.9In0.1MnO3 Yb0.8In0.2MnO3 HoMnO3 Tb0.9Sn0.1MnO3 Yb0.7Ho0.3MnO3 YbMnO3(Single Crystal) HoMnO3(Single Crystal) DyMnO3(Single Crystal) HoMnO3(Single Crystal) YbMnO3 Yb0.95Mg0.05MnO3 Yb0.9Er0.1MnO3 Yb0.8Er0.2MnO3 TbMnO3(Single Crystal) Tb0.6Dy0.4MnO3 GdMnO3 TbMnO3 DyMnO3 GdMnO3 (Single Crystal) TbMnO3 Tb0.67Dy0.33MnO3 Tb0.67Y0.33MnO3 Tb0.67Ho0.3MnO3 DyMnO3 (Single Crystal)
8 8 18 25 9 9 12 12 9.5 9 9 9 9 10 11 10 10 7 7 12 12 12 12 7
100 100 70 30 100 80 80 80 70 100 100 80 80 70 50 50 50 50 80 50 50 50 50 80
different then these are shown against the compound, 2.34 ± 0.35 2.64 ± 0.38 12.5 (J kg-1K-1) -4 (J kg-1K-1) 3.75 ± 6 0.78 2.3 5.2 5.5 13.1 (J kg-1K-1) 3.02 ± 0.37 2.63 ± 0.36 2.0 2.1 18(J kg-1K-1) 0.83 1.27 1.08 4.07 31.8 (J kg-1K-1) 6.75 ( J kg-1K-1) 5.25 ( J kg-1K-1) 5.15 ( J kg-1K-1) 6.63 ( J kg-1K-1) 13 ( J kg-1K-1)
different then these are shown against the compound, 38.03 ± 9 40.90 ± 10 312 (J kg-1) -90.0 ± 6 27 26 144 155 320 (J kg-1) 41 ± 9 40.0 ± 10 23.1 23.8 390 (J kg-1) 10 ---95 (J kg-1) 103 (J kg-1) 56 (J kg-1) 63 (J kg-1) 48 (J kg-1) 250 (J kg-1)
Our work Our work 6 7 8 13 13 13 14 15 15 16 16 17 18 19 19 19 20 21 21 21 21 22
For magnetic materials with second order transition, -ΔSMax is predicted to be proportional to H2/3[23]. For the present In doped YbMnO3 samples, the observed linear dependence of -ΔSMax versus H2/3 (shown in fig.5 (a, b) confirms the second order transition.
9
Fig 5. Maximum magnetic entropy change (|ΔSMax|) vs H2/3for (a) Yb0.9In0.1MnO3 and (b)Yb0.8In0.2MnO3 and universal curve constructed from the normalized entropy change (|S/SMax|)vs rescaled temperature () for different magnetic field for (c) Yb0.9In0.1MnO3 and (d) Yb0.8In0.2MnO3.
Now, we construct the universal curve of for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 by using the method with two reference temperature points [24]. The magnetic entropy change has to be rescaled to the normalized entropy change (ΔS /ΔSMax). The temperature axis has to be rescaled to a reduced temperature () by considering two reference temperatures Tr1 and Tr2,
10
In this work, we selected Tr1 and Tr2 such that ΔS(Tr1,2) = 1/2 ΔSMax [24]. Figure 5 (c) and (d) show normalized entropy change (|S/SMax|) vs rescaled temperature () for different magnetic fields for the two samples. We can notice that all the normalized entropy change curves merge onto one universal curve, as expected for the second-order ferromagnetic ordering transition. 4. Conclusion Magnetic and magnetocaloric properties of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 are reported here. Maximum entropy change observed at a field ΔH = 100 KOe is 2.34 ± 0.35 J/mole-K for Yb0.9In0.1MnO3and 2.64 ± 0.38 J/mole-K and Yb0.8In0.2MnO3. For similar field change of ΔH = 100 KOe, the values of relative cooling power are 38.03 ± 9 J /mol, and 40.90 ± 10 J/mol for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 respectively. The second order phase transition is confirmed by observing the merging of rescaled ΔSMax vs. T curves for various fields fit into a single curve. These compounds have RCP higher than that of pure YbMnO3. It may be a potential candidate as a magnetic refrigerant at low temperatures.
Acknowledgement BSB acknowledges UGC-DAE CSR, Mumbai, for the finical support in the form of project fellowship (project # CRS-M-199). AKB is thankful to the National Academy of Sciences (India) for their support.
References [1] V.K. Pecharsky, K.A. Gschneidner Jr., Phys. Rev. Lett. (1997);78: 4494. [2] S.FujiedaA. Fujita, and K. Fukamichi, Appl. Phys.Lett.(2002);81: 1276.
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[3] O.Tegus, E. Brück, K. H. J. Buschowand F. R. de Boer., Nature , (2002);415: 150. [4] Z. B. Guo, Y. W. Du, J. S. Zhu, H. Huang, W. P. Ding, and D. FengPhys. Rev. Lett. (1997);78: 1142. [5] A. Midya, P. Mandal,S. Das, S. Banerjee, L. S. Sharath Chandra, V. Ganesan and S. Roy Barman, Appl. Phys. Lett.(2010);96: 142514. [6] Shao Mingjie, Cao Shixun, Yuan Shujuan, Shang Jin, Kang Baojuan, Lu Bo, et al. Appl Phys Lett.,(2012);100:222404. [7] Wolff Fabris F, Pekala M, Drozd V, Fagnard J F, VanderbemdenPh, Liu Ru-Shi, et al. J Appl Phys (2007);101:103904. [8] B. Sattibabu, A. K. Bhatnagar, K. Vinod, Awadhesh Mani and D. Das, Appl. Phys. Lett. (2015); 107: 262904. [9] B. Sattibabu, A. K. Bhatnagar, S.,Rayaprol, D. Mohan, D. Das, M. Sundararaman and V. Siruguri, Physica B,(2014); 448: 210. [10] X. Fabree ´ges, I. Mirebeau, P. Bonville, S. Petit, G. Lebras-Jasmin, A. Forget, G. Andre, and S. Pailhes, Phys. Rev. B. (2008);78: 214422. [11] A. Arrott and J. Noakes, Phys. Rev. Lett. (1967);19: 786. [12] Karpasyuk V, Beznisko E and Abdullina. A, J. Magn. Magn. Mater. (2004); 750: 272-276 [13] A. Midya, S. N. Das, P. Mandal, S. Pandya and V. Ganesan,Phys. Rev. B., (2011); 84: 235127. [14] A. Midya, P. Mandal, S. Das, S. Banerjee, L. S. SharathChandra, V. Ganesan and S. Roy Barman, Appl. Phys. Lett., (2010);96: 142514. [15] B. Sattibabu, A. K. Bhatnagar, K. Vinod, S.,Rayaprol, A. Mani V. Siruguri, and D. Das, RSc advance ,(2016); 6: 48636.
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[16] B. Sattibabu, A. K. Bhatnagar, D.Singh, S.,Rayaprol, D. Das, and V.Ganesan, Mater. Lett. (2015); 161: 419-422. [17] Jin-Ling Jin, Xiang-Qun Zhang, Guo-Ke Li, and Zhao-Hua Cheng Phys. Rev. B , (2011); 83:184431. [18] N. Pavan Kumar and P. Venugopal Reddy, Mater. Lett. (2014); 132: 82–85. [19] N. Pavan Kumar and P. Venugopal Reddy, Mater. Lett. (2014); 122: 292–295. [20] Aditya A Wagh, K G Suresh, P S Anil Kumar and Suja Elizabeth, J .Phys D Apply physics (2015); 48:135001. [21] M. Staruch , L. Kuna , A. McDannald , M. Jain J. Magn. Magn. Mater (2015); 377: 117120. [22] M. Balli, S. Jandl , P. Fournier, S. Mansouri , A. Mukhin , Yu.V. Ivanov and A.M. Balbashov J. Magn. Magn. Mater (2015); 374: 252-257. [23] H.Oesterreicher and F.T. Parker, J. Appl. Phys. (1984); 55: 4334. [24] Q. Y. Dong, H. W. Zhang,J. R. Sun, B. G. Shen, and V. Franco, J. Appl. Phys., (2008);103:116101.
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www.elsevier.com/locate/physb
PII: DOI: Reference:
S0921-4526(17)30137-0 http://dx.doi.org/10.1016/j.physb.2017.03.024 PHYSB309868
To appear in: Physica B: Physics of Condensed Matter Received date: 10 January 2017 Revised date: 15 March 2017 Accepted date: 16 March 2017 Cite this article as: Bhumireddi Sattibabu, A.K. Bhatnagar, K. Vinod and Awadhesh Mani, Magnetocaloric effect in In doped YbMnO 3, Physica B: Physics of Condensed Matter, http://dx.doi.org/10.1016/j.physb.2017.03.024 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 galley proof before it is published in its final citable 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.
Magnetocaloric effect in In doped YbMnO3 Bhumireddi Sattibabu1,2*, A. K. Bhatnagar3, , K. Vinod4, Awadhesh Mani4 1
School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India
2
Department of Electronics and Physics, Institute of Science, GITAM University, Visakhapatnam 530045, India 3
4
School of Physics, University of Hyderabad, Hyderabad 500046, India
Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam - 603102, India
[email protected] [email protected] *
Corresponding authors: Dr. B. Sattibabu School of Engineering Sciences and Technology,
University of Hyderabad – 500046 INDIA Tel.: +91-40-23134301 / 23013200, Fax: +91-4023010227
Abstract Magnetic and magnetocaloric (MCE) properties of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 polycrystalline samples are presented in this paper. Isothermal magnetization measurements reveal a field induced magnetic transition. Magnetic entropy change of 2.34 ± 0.35 J/mole-K for Yb0.9In0.1MnO3 and 2.64 ± 0.38 J/mole-K for Yb0.8In0.2MnO3 field change ΔH = 10 KOe is observed around the ferromagnetic ordering temperature of Yb3+. Values of relative cooling power for the same field change are found to be 38.03 ± 9 J /mol, and 40.90 ± 10 J/mol for
1
Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3, respectively. These values suggest In doped YbMnO3 may be a potential candidate for magnetic refrigerant at low temperatures. Keywords Magnetic materials; Ceramics; Thermal properties; Magnetic entropy
1. Introduction Magnetocaloric refrigeration systems of much research interest in recent times. Magnetocaloric materials are generally characterized by the parameters like maximum magnetic entropy change (ΔSMax), Relative Cooling Power (RCP) and adiabatic temperature change (ΔTad). Many magnetic materials such as Gd5(Si2-xGe2+x) [1], LaFe13-xSix [2], MnFeP1-xAsx [3] and rare earth manganites [4] etc have been reported to have large magnetic entropy change under an applied magnetic field near magnetic phase transitions. Magnetocaloric properties of multiferroic rare earth manganites are worth investigating [5] and there are several works which have reported magnetocaloric properties of multiferroic rare earth manganites [6,7]. Systems showing large MCE in the low-temperature region from about 10 K down to sub-Kelvin are important for basic research as well as for specific technological applications such as space science and liquefaction of hydrogen in fuel industry. In our previous paper Yb1-xHoxMnO3 (x = 0.1, 0.2 and 0.3) large MCE properties were observed which were interpreted due to the higher magnetic moment of Ho3+ in these compounds [8]. Thus, in order to clarify the factors affecting the magnetocaloric properties of the multiferroic YbMnO3 and related materials, it is of important to study doped YbMnO3 systems with nonmagnetic substitutions as well. InMnO3, has a similar hexagonal structure as that of YbMnO3. The size of In3+ ion (0.925 Å) is only slightly smaller than Yb3+ ion size (0.985 Å), The field 2
induced magnetic transition observed in Yb1-xInxMnO3 has motivated us to investigate the magnetocaloric behavior in this system. Particularly, we are interested in studying the nature of the magnetic entropy change ΔSM and relative cooling power (RCP) in this compound at the Yb3+ ordering transition which takes place at a low temperature. In this work magnetocaloric properties of In doped polycrystalline YbMnO3 samples presented using magnetization measurements. 2. Experimental Details Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples were synthesized by solid state reaction method following a similar procedure as described in ref 9. The samples were characterized by powder x-ray diffraction (XRD) with Cu-Kα radiation (using Bruker D8 Advance X-ray powder diffractometer) and by magnetization measurements (using a commercial vibrating sample magnetometer (VSM): Cryogenic Inc. (UK)). 3. Results and Discussions Figure 1 shows XRD data of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3compounds. No impurity phase is detected and the XRD pattern is indexed using the hexagonal P63cm space group [10]. Lattice parameter values are a ~ 0.601 ± 0.002 nm c ~ 1.135 ± 0.005 nm for Yb0.9In0.1MnO3 and a ~ 0.603 ± 0.002 nm c ~ 1.136 ± 0.004 nm for Yb0.8In0.2MnO3 compounds. The doped lattice parameter is slightly lower than that of undoped one which may be due to small size of In 3+ ion compared to the Yb3+ ion size [10]. Among the Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples the lattice parameters do not vary significantly. This may be due to the fact that the actual In content may be slightly different from the expected/nominal levels or lattice strains.
3
Fig 1. XRD pattern for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 collected at room temperature.
Fig 2 shows temperature (T) dependence of zero field cooled (ZFC) magnetic susceptibility () and its inverse (1/) for the Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 compounds. Data clearly show two magnetic transitions ; first around the Neel temperature (TN) ~ 89 K corresponding to the AFM ordering of the Mn3+ moments and second around the Curie temperatures (TC) ~ 3.8 K corresponding to the ferromagnetic (FM) ordering of Yb3+ moments. Both magnetic transitions are well established and documented for pure and doped YbMnO3 in the literature [9,10]. Two transitions are shown for Yb0.8In0.2MnO3 sample in the zoomed plots given as insets of figure 2. The left inset shows first derivative of vs T around the Yb3+ ordering temperature and the right inset shows first derivative of 1/ vs T around the Mn3+ ordering temperature. The value of Neel temperature (TN) is 89 ± 1 K which is slightly higher than reported for polycrystalline YbMnO3
4
at 85 ± 1 K[10], and is due to the slight reduction in lattice parameter; which reduces the Mn-O bond lengths and strengthen the exchange interactions and therefore for the increase the TN [9]. 1/ vs T data shows linear Curie–Weiss (CW) behavior for T >> TN. Curie temperature (θcw) and effective magnetic moment (μeff) extracted from the Curie-Weiss fit are θcw = -156.7 ± 1.1 K, μeff = 6.02 ± 0.02 µB for Yb0.9In0.1MnO3 and θcw = -160.4 ± 1.5 K and μeff = 6.28 ± 0.02 µB for Yb0.8In0.2MnO3.The negative value of θcw obtained by fitting data points only above TN indicates presence of antiferromagnetic interaction.
Fig.2 Temperature dependence of χ and 1/χ with Curie–Weiss fit of Yb0.9In0.1MnO3 (filled red symbols) and Yb0.8In0.2MnO3 (open black symbols). Upper inset: of Yb3+and lower inset:
( )
of T near the FM transition
of curves of T near the AFM transition of Mn3+ for Yb0.8In0.2MnO3.
5
Fig. 3a shows isothermal magnetization (M-H) curves for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples, respectively, measured under applied magnetic field ranging from 0 to 100 kOe and between 2.5–38 K. A sudden slope change of M vs H at magnetic field ~ 30 kOe is observed and is due to the field-induced magnetic transition. A similar behavior has been observed in some other doped YbMnO3 samples [8]. Fig 3b shows the corresponding Arrott plots (H/M vs M2) for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples, respectively. Both samples exhibit a second order field induced magnetic transition as the Arrots plots have positive slope [11].
2
Fig 3. (a) Field dependence of isothermal magnetization and (b) Arrott plots of H/M vs M at
various temperatures for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3.
6
To obtain the magnetocaloric properties of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 samples, total magnetic entropy change ΔSM is calculated using Maxwell equations given below [12]: (
)
(
)
∫
(
)
(1)
which is approximated to ∑
(2)
Fig 4 Variation of magnetic entropy change (ΔSM) with temperature for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3.Inset figure shows RCP as a function of field.
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Figure 4 shows variation in magnetic-entropy change (ΔSM) as a function of temperature for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 at ΔH = 2, 4, 6, 8, and 10 kOe. As seen from Fig. 4, the maximum magnetic entropy change ΔSMax increases with increasing field change. Position of the ΔSMax shifts from 4.5 to 7.5 K as ΔH increases from 2 to 10 kOe. The ΔSMax value is 2.34 ± 0.35 J/mole-K for Yb0.9In0.1MnO3 and is 2.64 ± 0.38 J/mole-K for Yb0.8In0.2MnO3 at a field change of ΔH= 100 kOe. The field induced transition contributes to increase of ΔSMax. The relative cooling power (RCP) of the samples calculated as, RCP S Max TFWHM and RCP values are 38.03 ± 9 J /mol for Yb0.9In0.1MnO3 and 40.90 ± 10 J/mol for Yb0.8In0.2MnO3 with ΔH = 100 kOe. RCP increases with increasing field change as shown inset in the fig 4. ΔSMax and RCP values of the present materials are higher than reported for a single crystal YbMnO3 [13] and comparable to reported perovskite manganites listed in Table 1.
Table.1. Maximum entropy change and RCP of Yb1- xInxMnO3 (x = 0.1 and 0.2) samples Compared with reported values.
Composition
TPeak (K)
ΔH (kOe)
ΔSMmax (J mol-1K-1) If units are 8
RCP (J mol-1) If units are
References
Yb0.9In0.1MnO3 Yb0.8In0.2MnO3 HoMnO3 Tb0.9Sn0.1MnO3 Yb0.7Ho0.3MnO3 YbMnO3(Single Crystal) HoMnO3(Single Crystal) DyMnO3(Single Crystal) HoMnO3(Single Crystal) YbMnO3 Yb0.95Mg0.05MnO3 Yb0.9Er0.1MnO3 Yb0.8Er0.2MnO3 TbMnO3(Single Crystal) Tb0.6Dy0.4MnO3 GdMnO3 TbMnO3 DyMnO3 GdMnO3 (Single Crystal) TbMnO3 Tb0.67Dy0.33MnO3 Tb0.67Y0.33MnO3 Tb0.67Ho0.3MnO3 DyMnO3 (Single Crystal)
8 8 18 25 9 9 12 12 9.5 9 9 9 9 10 11 10 10 7 7 12 12 12 12 7
100 100 70 30 100 80 80 80 70 100 100 80 80 70 50 50 50 50 80 50 50 50 50 80
different then these are shown against the compound, 2.34 ± 0.35 2.64 ± 0.38 12.5 (J kg-1K-1) -4 (J kg-1K-1) 3.75 ± 6 0.78 2.3 5.2 5.5 13.1 (J kg-1K-1) 3.02 ± 0.37 2.63 ± 0.36 2.0 2.1 18(J kg-1K-1) 0.83 1.27 1.08 4.07 31.8 (J kg-1K-1) 6.75 ( J kg-1K-1) 5.25 ( J kg-1K-1) 5.15 ( J kg-1K-1) 6.63 ( J kg-1K-1) 13 ( J kg-1K-1)
different then these are shown against the compound, 38.03 ± 9 40.90 ± 10 312 (J kg-1) -90.0 ± 6 27 26 144 155 320 (J kg-1) 41 ± 9 40.0 ± 10 23.1 23.8 390 (J kg-1) 10 ---95 (J kg-1) 103 (J kg-1) 56 (J kg-1) 63 (J kg-1) 48 (J kg-1) 250 (J kg-1)
Our work Our work 6 7 8 13 13 13 14 15 15 16 16 17 18 19 19 19 20 21 21 21 21 22
For magnetic materials with second order transition, -ΔSMax is predicted to be proportional to H2/3[23]. For the present In doped YbMnO3 samples, the observed linear dependence of -ΔSMax versus H2/3 (shown in fig.5 (a, b) confirms the second order transition.
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Fig 5. Maximum magnetic entropy change (|ΔSMax|) vs H2/3for (a) Yb0.9In0.1MnO3 and (b)Yb0.8In0.2MnO3 and universal curve constructed from the normalized entropy change (|S/SMax|)vs rescaled temperature () for different magnetic field for (c) Yb0.9In0.1MnO3 and (d) Yb0.8In0.2MnO3.
Now, we construct the universal curve of for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 by using the method with two reference temperature points [24]. The magnetic entropy change has to be rescaled to the normalized entropy change (ΔS /ΔSMax). The temperature axis has to be rescaled to a reduced temperature () by considering two reference temperatures Tr1 and Tr2,
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In this work, we selected Tr1 and Tr2 such that ΔS(Tr1,2) = 1/2 ΔSMax [24]. Figure 5 (c) and (d) show normalized entropy change (|S/SMax|) vs rescaled temperature () for different magnetic fields for the two samples. We can notice that all the normalized entropy change curves merge onto one universal curve, as expected for the second-order ferromagnetic ordering transition. 4. Conclusion Magnetic and magnetocaloric properties of Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 are reported here. Maximum entropy change observed at a field ΔH = 100 KOe is 2.34 ± 0.35 J/mole-K for Yb0.9In0.1MnO3and 2.64 ± 0.38 J/mole-K and Yb0.8In0.2MnO3. For similar field change of ΔH = 100 KOe, the values of relative cooling power are 38.03 ± 9 J /mol, and 40.90 ± 10 J/mol for Yb0.9In0.1MnO3 and Yb0.8In0.2MnO3 respectively. The second order phase transition is confirmed by observing the merging of rescaled ΔSMax vs. T curves for various fields fit into a single curve. These compounds have RCP higher than that of pure YbMnO3. It may be a potential candidate as a magnetic refrigerant at low temperatures.
Acknowledgement BSB acknowledges UGC-DAE CSR, Mumbai, for the finical support in the form of project fellowship (project # CRS-M-199). AKB is thankful to the National Academy of Sciences (India) for their support.
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