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Impact of small Er rare earth element substitution on magnetocaloric properties of (La0.9Er0.1)0.67Pb0.33MnO3 perovskite
Journal of Molecular Structure 1196 (2019) 658e661
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Impact of small Er rare earth element substitution on magnetocaloric properties of (La0.9Er0.1)0.67Pb0.33MnO3 perovskite € nül Akça b, *, Ahmet Ekicibil b Selda Kılıç Çetin a, Go a b
Çukurova University, Central Research Laboratory, Adana, Turkey Çukurova University, Faculty of Sciences and Letters, Department of Physics, Adana, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 February 2019 Received in revised form 20 March 2019 Accepted 4 July 2019
In this work, the effect of Er substitution on the magnetic and magnetocaloric properties has been studied for (La0.9Er0.1)0.67Pb0.33MnO3 perovskite synthesized by the sol-gel procedure. Magnetization measurements performed as a function of both temperature and magnetic field in order to determine magnetic and magnetocaloric properties. The temperature dependence of magnetization measured under 5 mT magnetic field indicate that sample exhibits ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. The Curie temperature (TC) decreases with Er-doping from 358 K for La0.67Pb0.33MnO3 to 349 K. From the isothermal magnetization measurements taken up to 5T around the TC in 3 K intervals, the magnetic entropy change (DSM ) values of the sample have been determined value has been calculated as 0.98, 1.73, 2.33, 2.85 and 3.23 for different magnetic fields. The DSmax M Jkg1K1 for 1, 2, 3, 4 and 4.8 T, respectively. The type of magnetic phase transition has been determined as the second order from the slope of Arrott plots. © 2019 Elsevier B.V. All rights reserved.
Keywords: Magnetocaloric effect Magnetic refrigeration Curie temperature Manganites
1. Introduction In recent times, studies related to refrigeration systems taken part our daily lives in many fields have been attracted significant attention. Nowadays, the cooling applications are made with conventional gas compression/expansion systems. But, it is known that these systems may cause very important damages for our living environment such as ozone depletion or global warming hazard and toxicity [1e3]. Besides, energy consumption is quite high [4,5]. With these reasons, research groups have been seeking to find new cooling systems for years. Recently, many groups have concentrated on magnetic refrigeration (MR) systems. These systems are reliable, harmless, compactness and silent when compared with conventional systems [6]. Because of these advantageous properties over the other systems, these systems are thought to be an alternative technology [7e9]. Magnetocaloric effect (MCE) depicted as the change observed in the temperature of a magnetic material depending on the entropy change is the working principle of the MR systems [10]. For MR systems, many materials since discovered of MCE have
* Corresponding author. Department of Physics, Faculty of Sciences and Letters, Çukurova University, 01330, Adana, Turkey. E-mail address: [email protected] (G. Akça). https://doi.org/10.1016/j.molstruc.2019.07.017 0022-2860/© 2019 Elsevier B.V. All rights reserved.
been produced and searched the magnetocaloric properties of these materials [11e15]. Among them, manganites formulized with Ln1xMxMnO3 (Ln ¼ rare earth element and M ¼ monovalent and divalent element) [14] have been intensively worked out because of their significant properties such as cheap material supply, convenient sample production method, smaller thermal and field hysteresis [14]. The magnetic and magnetocaloric properties of the manganites are affected by many parameters such as A-site cationic size mismatch [16] and the cationic disorder depended on doping level [17]. We have worked out the effect of small Er rare earth element doping on the magnetic and magnetocaloric properties of (La0.9Er0.1)0.67Pb0.33MnO3 perovskite. 2. Experimental details In this work, the Er-doped (La0.9Er0.1)0.67Pb0.33MnO3 perovskite compound labeled as LEPM was obtained by the sol-gel technique using La2O3, Pb(NO3)2, Er(NO3)3 and Mn(NO3)2.4H2O initial materials. Stoichiometric amounts of initial powders were dissolved in convenient solvent and ethylene glycol and citric acid were added to mix. Afterward, till dry-gel was formation was obtained the solution was stirred and heated. The obtained sample was treated at 550 C for 5 h. Then, the sample, which was grounded by using an agat mortar, was pressed into pellet form. The final material
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sintered at 975 C during 24 h in air. By an x-ray diffractometer (XRD) has been investigated out the structural analysis of the sample and the grain structure of the sample was viewed by a scanning electron microscope (SEM). By using a superconducting quantum interface device magnetometer was performed the magnetization measurements as a function of temperature (M(T)) at zero field cooling (ZFC) and field cooling (FC) modes, and isothermal magnetization measurements (M(H)) are made around TC. 3. Results and discussion The XRD pattern of the LEPM manganite compound is given in Fig. 1. The results of the XRD analysis represent that the sample has perovskite structure. It is seen from the XRD pattern belonging to the sample that the sample contains a very small amount of impurity phase related with Mn3O4 and ErMn2O5 phases. It is thought that the presence of these impurities arises from the elements which are not reacted. Because these impurity phases have paramagnetic properties they do not make a contribution to observed magnetization behavior [19,20]. The sample is indexed in orthorhombic symmetry (space group, Pnma). The lattice parameters of the sample are found as a ¼ 5.46(Å), b ¼ 7.79(Å), c ¼ 5.58(Å), respectively. The unit cell volume (V) of the sample is V ¼ 237.34(Å3). The crystal symmetry of the sample is similar to undoped LPM sample examined in our previous work [18,21]. The SEM image of the sample at 40kx magnification is given in Fig. 2. The sample forms from aggregated grains which has a polygonal form grain size of range from 0.05 mm to 0.95 mm. The average grain size has been found as 0.43 mm from 100 arbitrary grains. EDX results have been showed that the sample includes all expected elements and does not have any extrinsic elements. In order to investigate the temperature-dependent magnetic behavior of the sample, both at the ZFC and FC mode, the M(T) measurements were made under 5 mT. The low field thermomagnetic curves of the sample are presented in Fig. 3. The sample shows from PM to FM phase transition with decreasing temperature. Besides, the curves of the ZFC and FC magnetization separate from each other at low temperatures. This irreversibility may result from intrinsic magnetic anisotropy, canted nature of the spins, randomly freezing of spins, and domain wall pinning effect [22,23]. To identify the TC of the sample we have constructed the dM/dT - T curve.
Fig. 2. The SEM image of the LEPM sample at 40kx magnification.
Fig. 3. The M(T) curves of the sample at ZFC-FC modes under 5 mT magnetic field.
From the minimum point of this graph, TC of the sample is found as 349 K. The TC value of the undoped La0.67Pb0.33MnO3 (LPM) is determined as 358 K in our previous work [20,21]. The decrease observed in TC may arise from the change of the average A-site cation size because of the different ionic radii [24]. To calculate the DSM around TC, the M(H) curves were obtained at different temperatures at various magnetic fields up to 4.8 T are given in Fig. 4. The M(H) curves below TC show an abrupt increase with the magnetic field and nearly approach to saturation which is characteristic for ferromagnetic materials. Above TC, these curves change linearly with increasing magnetic field. The linear change is characteristic property of the paramagnetic materials. The DSM of the sample can be calculated using [25];
DSM ðH; TÞ ¼
Fig. 1. XRD pattern of LEPM sample.
X Mi Miþ1 Tiþ1 Ti
DHi :
(1)
In Eq. (1), Mi and Miþ1 magnetizations are the values corresponding to Ti and Tiþ1, respectively. By using the Eq. (1) and experimental M(H) isotherms, we have calculated the temperature dependent of the DSM at different magnetic fields of 1e4.8T as shown in Fig. 5. Fig. 5 represents the temperature dependence of the DSM , the DSM values show an increase with increasing of the
660
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LEPM sample are comparable to other perovskite materials reported in the literature [18,27e34]. In magnetic cooling technology, the effectiveness of a magnetocaloric material depends on relative cooling power (RCP) which corresponds to the amount of heat transferred in the cooling cycle and is defined as dTFWHM (where dTFWHM is a full width at half RCP ¼ DSmax M maximum value of the temperature change) [14,35]. For the LPEM sample, the RCP values were calculated as 26.46, 48.44, 72.81, 99.75 and 118.70 Jkg-1 for 1, 2, 3, 4, and 4.8 T, respectively. For comparision, RCP values of several similar perovskite structures are given in the Table 1. The order of the magnetic phase transition is important for materials exhibiting magnetocaloric properties and it can be described from the Arrott plots (H/M- M2 curves) constructed from the M(H) data. If the sign of the slope of these curves near TC is positive the transition is second order. If negative, it is first [36]. In Fig. 6, the Arrott plots of the sample are presented. It is seen from the Arrott plots that the curves have positive slope around TC. This states that the transition is second order. Fig. 4. The M(H) isotherms of the sample near TC.
4. Conclusions The structural, magnetic and magnetocaloric properties of the small Er doped (La0.9Er0.1)0.67Pb0.33MnO3 perovskite were investigated. The sample is indexed in orthorhombic structure (Pnma space group). Thermomagnetic measurements show that the sample undergoes a FM-PM phase transition at 349 K. This value is
Fig. 5. The DSM ðTÞ curves of the sample under different magnetics fields around TC.
magnetic field. This increment arise from the number of magnetic moments converged in the direction of the magnetic field with increasing of the magnetic field [26] and reach up to a maximum value called as maximum magnetic entropy change (DSmax M ) near value reaches 0.98, 1.73, 2.33, 2.85 and 3.23 the TC. The DSmax M values of Jkg1K1 for 1, 2, 3, 4 and 4.8 T, respectively. The DSmax M
Fig. 6. Arrott plots of the sample.
Table 1 Summary of DSmax and RCP values for some magnetocaloric samples at different magnetic fields. M Sample
m0H (T)
DS max (Jkg1K1) M
RCP (Jkg1)
Refs.
Gd La0.85K0.15MnO3 La0.85Ag0.15MnO3 (La0.9Er0.1)0.67Pb0.33MnO3 La0.67Pb0.33MnO3 La0.67Pb0.33MnO3 La0.7Pb0.3MnO3 Pr0.55Sr0.35K0.1MnO3 PrSr0.6Pb0.4Mn2O6 La0.6Sr0.2Na0.2MnO3
1 2 2 2 5 2 1.35 2 5 5
3.25 4.63 4.40 3.23 4.43 2.33 1.53 2.20 3.68 3.57
e 78.41 79.17 48.44 180.07 106.27 53 85.95 283 214.46
[27] [28] [29] This work [18] [30] [31] [32] [33] [34]
S.K. Çetin et al. / Journal of Molecular Structure 1196 (2019) 658e661
lower than that in La0.67Pb0.33MnO3 which is about 358 K. It is obvious that the Curie temperature decreases with the substitution of Er with La because of the decreasing of A-site cation size. The maximum magnetic entropy change was determined as 0.98, 1.73, 2.33, 2.85 and 3.23 Jkg1K1 for a field change of 1, 2, 3, 4 and 4.8T, respectively. Acknowledgement This work is supported by the Research Fund of Çukurova University, Adana, Turkey, under grant contracts no. FEF2010D4. References [1] E. Brück, J. Phys. D Appl. Phys. 38 (2005) R381eR391. [2] K.A. Gschneidner Jr., V.K. Pecharsky, A.O. Tsokol, Rep. Prog. Phys. 68 (2005) 1479e1539. [3] A.R. Shelke, A.V. Ghule, Y.P. Lee, C.D. Lokhande, N.G. Deshpande, J. Alloy. Comp. 692 (2017) 522e528. [4] A. Rostamnejadi, M. Venkatesan, P. Kameli, H. Salamati, J.M.D. Coey, J. Magn. Magn. Mater. 323 (2011) 2214e2218. [5] https://www.eia.gov/todayinenergy/. [6] E. Sellami-Jmal, A. Ezaami, W. Cheikhrouhou-Koubaa, A. Cheikhrouhou, J. Magn. Magn. Mater. 465 (2018) 762e767. [7] H. Szymczak, R. Szymczak, Materials Science-Poland 26 (4) (2008) 807e814. [8] B.F. Yu, Q. Gao, B. Zhang, X.Z. Meng, Z. Chen, Int. J. Refrig. 26 (2003) 622e636. [9] Za Mohamed, E. Tka, J. Dhahri, E.K. Hlil, J. Alloy. Comp. 615 (2014) 290e297. [10] A.M. Tishin, Y.I. Spichkin, The Magnetocaloric Effect and its Applications, IOP Publishing LTD, 2003. [11] V.K. Pecharsky, K.A. Gschneidner, Giant magnetocaloric effect in Gd5(Si2Ge2), Phys. Rev. Lett. 23 (1997), 4494e4497. [12] F.X. Hu, B.G. Shen, J.R. Sun, Z.H. Cheng, G.H. Rao, X.X. Zhang, Appl. Phys. Lett. 23 (2001) 3675e3677. [13] O. Tegus, E. Brück, K.H.J. Buschow, F.R. de Boer, Nat. Lond. 415 (2002) 150e152.
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[14] M.H. Phan, S.C. Yu, Review of the magnetocaloric effect in manganite materials, J. Magn. Magn. Mater. 308 (2007) 325e340. [15] V. Franco, J.S. Blazquez, J.J. Ipus, J.Y. Law, L.M. Moreno-Ramirez, A. Conde, Prog. Mater. Sci. 93 (2018) 112e232. [16] L.M. Rodriquez-Martinez, J.P. Atfield, Phys. Rev. B 54 (1996). R15 622- R15 625. [17] P. Levy, F. Parisi, G. Polla, D. Vega, G. Leyva, H. Lanza, Phys. Rev. B 62 (2000) 6437e6441. [18] S.K. Çetin, M. Acet, A. Ekicibil, J. Alloy. Comp. 727 (2017) 1253e1262. [19] B. Boucher, R. Buhl, M. Perrin, J. Appl. Phys. 42 (1971), 1615e1617. [20] J.A. Alonso, M.T. Casais, M.J. Martinez-Lope, J.L. Martinez, M.T. Fernandez-Diaz, J. Phys. Condens. Matter 9 (1997), 8515e8526. [21] S.K. Çetin, M. Acet, M. Günes¸, A. Ekicibil, M. Farle, J. Alloy. Comp. 650 (2015) 285e294. [22] J.C. Debnath, R. Zeng, J.H. Kim, P. Shamba, D.P. Chen, S.X. Dou, J. Alloy. Comp. 510 (2012), 125e133. [23] E. Tasarkuyu, A. Coskun, A. Irmak, S. Aktürk, G. Ünlü, Y. Samancıoglu, A. Yücel, C. Sarıkürkçü, S. Aksoy, M. Acet, J. Alloy. Comp. 509 (2011), 3717e3722. [24] Q.Q. Cao, J. Wu, K.M. Gu, S.Y. Zhang, Y.W. Du, J. Appl. Phys. 85 (1999), 4494e4496. [25] V.K. Pecharsky, K.A. Gschneidner Jr., J. Magn. Magn. Mater. 200 (1999) 44. [26] Soma Das, T.K. Dey, J. Alloy. Comp. 440 (2007) 30e35. €ldea ki, R. Chahine, and T. K. Bose, (1995)3528-3537. [27] M. Fo [28] G. Akça, S. Kılıç Çetin, M. Günes¸, A. Ekicibil, Ceram. Int. 42 (2016) 19097e19104. [29] A.O. Ayas¸, M. Akyol, A. Ekicibil, Phil. Mag. 96 (2016) 922e937. [30] M. Hsini, S. Khadhraoui, N. Zaidi, Z.A. Alrowaili, J. Supercond. Nov. Magnetism 31 (2018) 3717e3722. [31] N. Chau, H.N. Nhat, N.H. Luong, D.L. Minh, N.D. Tho, N.N. Chau, Physica B 327 (2003) 270. [32] A. Jerbi, R. Thaljaoui, A. Krichene, W. Boujelben, Physica B 442 (2014) 21e28. [33] A.O. Ayas¸, J. Supercond. Novel Magn. (2018). https://doi.org/10.1007/s10948018-4688-6. [34] S. Hcini, R. Charguia, A. Dhahri, M.L. Bouazizi, J. Supercond. Novel Magn. (2018). https://doi.org/10.1007/s10948-018-4988-x. lu, [35] E. Tas¸arkuyu, A. Cos¸kun, A.E. Irmak, S. Aktürk, G. Ünlü, Y. Samancıog A. Yücel, C. Sarıkürkçü, S. Aksoy, M. Acet, J. Alloy. Comp. 509 (2011) 3717e3722. [36] B.K. Banerjee, Phys. Lett. 12 (1964) 16e17.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Impact of small Er rare earth element substitution on magnetocaloric properties of (La0.9Er0.1)0.67Pb0.33MnO3 perovskite € nül Akça b, *, Ahmet Ekicibil b Selda Kılıç Çetin a, Go a b
Çukurova University, Central Research Laboratory, Adana, Turkey Çukurova University, Faculty of Sciences and Letters, Department of Physics, Adana, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 February 2019 Received in revised form 20 March 2019 Accepted 4 July 2019
In this work, the effect of Er substitution on the magnetic and magnetocaloric properties has been studied for (La0.9Er0.1)0.67Pb0.33MnO3 perovskite synthesized by the sol-gel procedure. Magnetization measurements performed as a function of both temperature and magnetic field in order to determine magnetic and magnetocaloric properties. The temperature dependence of magnetization measured under 5 mT magnetic field indicate that sample exhibits ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. The Curie temperature (TC) decreases with Er-doping from 358 K for La0.67Pb0.33MnO3 to 349 K. From the isothermal magnetization measurements taken up to 5T around the TC in 3 K intervals, the magnetic entropy change (DSM ) values of the sample have been determined value has been calculated as 0.98, 1.73, 2.33, 2.85 and 3.23 for different magnetic fields. The DSmax M Jkg1K1 for 1, 2, 3, 4 and 4.8 T, respectively. The type of magnetic phase transition has been determined as the second order from the slope of Arrott plots. © 2019 Elsevier B.V. All rights reserved.
Keywords: Magnetocaloric effect Magnetic refrigeration Curie temperature Manganites
1. Introduction In recent times, studies related to refrigeration systems taken part our daily lives in many fields have been attracted significant attention. Nowadays, the cooling applications are made with conventional gas compression/expansion systems. But, it is known that these systems may cause very important damages for our living environment such as ozone depletion or global warming hazard and toxicity [1e3]. Besides, energy consumption is quite high [4,5]. With these reasons, research groups have been seeking to find new cooling systems for years. Recently, many groups have concentrated on magnetic refrigeration (MR) systems. These systems are reliable, harmless, compactness and silent when compared with conventional systems [6]. Because of these advantageous properties over the other systems, these systems are thought to be an alternative technology [7e9]. Magnetocaloric effect (MCE) depicted as the change observed in the temperature of a magnetic material depending on the entropy change is the working principle of the MR systems [10]. For MR systems, many materials since discovered of MCE have
* Corresponding author. Department of Physics, Faculty of Sciences and Letters, Çukurova University, 01330, Adana, Turkey. E-mail address: [email protected] (G. Akça). https://doi.org/10.1016/j.molstruc.2019.07.017 0022-2860/© 2019 Elsevier B.V. All rights reserved.
been produced and searched the magnetocaloric properties of these materials [11e15]. Among them, manganites formulized with Ln1xMxMnO3 (Ln ¼ rare earth element and M ¼ monovalent and divalent element) [14] have been intensively worked out because of their significant properties such as cheap material supply, convenient sample production method, smaller thermal and field hysteresis [14]. The magnetic and magnetocaloric properties of the manganites are affected by many parameters such as A-site cationic size mismatch [16] and the cationic disorder depended on doping level [17]. We have worked out the effect of small Er rare earth element doping on the magnetic and magnetocaloric properties of (La0.9Er0.1)0.67Pb0.33MnO3 perovskite. 2. Experimental details In this work, the Er-doped (La0.9Er0.1)0.67Pb0.33MnO3 perovskite compound labeled as LEPM was obtained by the sol-gel technique using La2O3, Pb(NO3)2, Er(NO3)3 and Mn(NO3)2.4H2O initial materials. Stoichiometric amounts of initial powders were dissolved in convenient solvent and ethylene glycol and citric acid were added to mix. Afterward, till dry-gel was formation was obtained the solution was stirred and heated. The obtained sample was treated at 550 C for 5 h. Then, the sample, which was grounded by using an agat mortar, was pressed into pellet form. The final material
S.K. Çetin et al. / Journal of Molecular Structure 1196 (2019) 658e661
659
sintered at 975 C during 24 h in air. By an x-ray diffractometer (XRD) has been investigated out the structural analysis of the sample and the grain structure of the sample was viewed by a scanning electron microscope (SEM). By using a superconducting quantum interface device magnetometer was performed the magnetization measurements as a function of temperature (M(T)) at zero field cooling (ZFC) and field cooling (FC) modes, and isothermal magnetization measurements (M(H)) are made around TC. 3. Results and discussion The XRD pattern of the LEPM manganite compound is given in Fig. 1. The results of the XRD analysis represent that the sample has perovskite structure. It is seen from the XRD pattern belonging to the sample that the sample contains a very small amount of impurity phase related with Mn3O4 and ErMn2O5 phases. It is thought that the presence of these impurities arises from the elements which are not reacted. Because these impurity phases have paramagnetic properties they do not make a contribution to observed magnetization behavior [19,20]. The sample is indexed in orthorhombic symmetry (space group, Pnma). The lattice parameters of the sample are found as a ¼ 5.46(Å), b ¼ 7.79(Å), c ¼ 5.58(Å), respectively. The unit cell volume (V) of the sample is V ¼ 237.34(Å3). The crystal symmetry of the sample is similar to undoped LPM sample examined in our previous work [18,21]. The SEM image of the sample at 40kx magnification is given in Fig. 2. The sample forms from aggregated grains which has a polygonal form grain size of range from 0.05 mm to 0.95 mm. The average grain size has been found as 0.43 mm from 100 arbitrary grains. EDX results have been showed that the sample includes all expected elements and does not have any extrinsic elements. In order to investigate the temperature-dependent magnetic behavior of the sample, both at the ZFC and FC mode, the M(T) measurements were made under 5 mT. The low field thermomagnetic curves of the sample are presented in Fig. 3. The sample shows from PM to FM phase transition with decreasing temperature. Besides, the curves of the ZFC and FC magnetization separate from each other at low temperatures. This irreversibility may result from intrinsic magnetic anisotropy, canted nature of the spins, randomly freezing of spins, and domain wall pinning effect [22,23]. To identify the TC of the sample we have constructed the dM/dT - T curve.
Fig. 2. The SEM image of the LEPM sample at 40kx magnification.
Fig. 3. The M(T) curves of the sample at ZFC-FC modes under 5 mT magnetic field.
From the minimum point of this graph, TC of the sample is found as 349 K. The TC value of the undoped La0.67Pb0.33MnO3 (LPM) is determined as 358 K in our previous work [20,21]. The decrease observed in TC may arise from the change of the average A-site cation size because of the different ionic radii [24]. To calculate the DSM around TC, the M(H) curves were obtained at different temperatures at various magnetic fields up to 4.8 T are given in Fig. 4. The M(H) curves below TC show an abrupt increase with the magnetic field and nearly approach to saturation which is characteristic for ferromagnetic materials. Above TC, these curves change linearly with increasing magnetic field. The linear change is characteristic property of the paramagnetic materials. The DSM of the sample can be calculated using [25];
DSM ðH; TÞ ¼
Fig. 1. XRD pattern of LEPM sample.
X Mi Miþ1 Tiþ1 Ti
DHi :
(1)
In Eq. (1), Mi and Miþ1 magnetizations are the values corresponding to Ti and Tiþ1, respectively. By using the Eq. (1) and experimental M(H) isotherms, we have calculated the temperature dependent of the DSM at different magnetic fields of 1e4.8T as shown in Fig. 5. Fig. 5 represents the temperature dependence of the DSM , the DSM values show an increase with increasing of the
660
S.K. Çetin et al. / Journal of Molecular Structure 1196 (2019) 658e661
LEPM sample are comparable to other perovskite materials reported in the literature [18,27e34]. In magnetic cooling technology, the effectiveness of a magnetocaloric material depends on relative cooling power (RCP) which corresponds to the amount of heat transferred in the cooling cycle and is defined as dTFWHM (where dTFWHM is a full width at half RCP ¼ DSmax M maximum value of the temperature change) [14,35]. For the LPEM sample, the RCP values were calculated as 26.46, 48.44, 72.81, 99.75 and 118.70 Jkg-1 for 1, 2, 3, 4, and 4.8 T, respectively. For comparision, RCP values of several similar perovskite structures are given in the Table 1. The order of the magnetic phase transition is important for materials exhibiting magnetocaloric properties and it can be described from the Arrott plots (H/M- M2 curves) constructed from the M(H) data. If the sign of the slope of these curves near TC is positive the transition is second order. If negative, it is first [36]. In Fig. 6, the Arrott plots of the sample are presented. It is seen from the Arrott plots that the curves have positive slope around TC. This states that the transition is second order. Fig. 4. The M(H) isotherms of the sample near TC.
4. Conclusions The structural, magnetic and magnetocaloric properties of the small Er doped (La0.9Er0.1)0.67Pb0.33MnO3 perovskite were investigated. The sample is indexed in orthorhombic structure (Pnma space group). Thermomagnetic measurements show that the sample undergoes a FM-PM phase transition at 349 K. This value is
Fig. 5. The DSM ðTÞ curves of the sample under different magnetics fields around TC.
magnetic field. This increment arise from the number of magnetic moments converged in the direction of the magnetic field with increasing of the magnetic field [26] and reach up to a maximum value called as maximum magnetic entropy change (DSmax M ) near value reaches 0.98, 1.73, 2.33, 2.85 and 3.23 the TC. The DSmax M values of Jkg1K1 for 1, 2, 3, 4 and 4.8 T, respectively. The DSmax M
Fig. 6. Arrott plots of the sample.
Table 1 Summary of DSmax and RCP values for some magnetocaloric samples at different magnetic fields. M Sample
m0H (T)
DS max (Jkg1K1) M
RCP (Jkg1)
Refs.
Gd La0.85K0.15MnO3 La0.85Ag0.15MnO3 (La0.9Er0.1)0.67Pb0.33MnO3 La0.67Pb0.33MnO3 La0.67Pb0.33MnO3 La0.7Pb0.3MnO3 Pr0.55Sr0.35K0.1MnO3 PrSr0.6Pb0.4Mn2O6 La0.6Sr0.2Na0.2MnO3
1 2 2 2 5 2 1.35 2 5 5
3.25 4.63 4.40 3.23 4.43 2.33 1.53 2.20 3.68 3.57
e 78.41 79.17 48.44 180.07 106.27 53 85.95 283 214.46
[27] [28] [29] This work [18] [30] [31] [32] [33] [34]
S.K. Çetin et al. / Journal of Molecular Structure 1196 (2019) 658e661
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