DSpace at VNU: Large magnetic entropy change in Cu-doped manganites

ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 285 (2005) 199–203 www.elsevier.com/locate/jmmm Large magnetic entropy change in Cu-doped manganites Manh-Huong Phana,b,Ã, Hua-Xin Penga, Seong-Cho Yub, Nguyen Duc Thoc, Nguyen Chauc a Department of Aerospace Engineering, Bristol University, Queen’s Building, University Walk, Bristol, BS8 1TR, UK b Department of Physics, Chungbuk National University, Cheongju 361-763, South Korea c Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Vietnam Received November 2003; received in revised form 20 June 2004 Available online 17 August 2004 Abstract Magnetic entropy change above 300 K, which is larger than that of gadolinium (Phys Rev B 57 (1998) 3478), has been observed in a Cu-doped manganites of La0.7Sr0.3Mn1ÀxCuxO3 (x ¼ 0:05; 0:1) The large magnetic entropy change originated from a sharp magnetization jump is associated with a first-order crystallographic phase transition of the sample near the Curie temperature These results suggest that the present Cu-doped manganites are suitable candidate materials for magnetic refrigerants in the room temperature magnetic-refrigeration technology r 2004 Elsevier B.V All rights reserved PACS: 75.30.Sg; 75.30.Àm; 75.50.Ày Keywords: Magnetic entropy; Magnetic refrigeration; Cu-doped manganites Recently, several works have reported a large magneto-caloric effect (MCE) in polycrystalline [1–7] and single crystalline [8] manganese perovskite materials The MCE is an intrinsic thermodynamic property of magnetic solids, and manifests itself as an adiabatic temperature change closely related to the magnetic entropy change caused by the application of magnetic field Materials with large MCE have attracted growing ÃCorresponding author Tel.: +44 (0)117 928 7697; fax: +44 (0)117 927 2771 E-mail address: M.H.Phan@bristol.ac.uk (M.-H Phan) interest owing to the possible applications for magnetic refrigerants [2,5,7,8] In general, there are two basic requirements for a magnetic material to possess a large MCE One is a large spontaneous magnetization (such as in the case of a heavy rareearth metal, Gd, for example) [9,10], the other is a sharp drop in magnetization with increasing temperature, which is associated with the ferromagnetic-paramagnetic transition at the Curie temperature found in perovskite manganites [1–7] Additionally, considerable coupling between spin and lattice in the magnetic ordering process in perovskite manganites was believed to occur and 0304-8853/$ - see front matter r 2004 Elsevier B.V All rights reserved doi:10.1016/j.jmmm.2004.07.041 ARTICLE IN PRESS 200 M.-H Phan et al / Journal of Magnetism and Magnetic Materials 285 (2005) 199–203 result in an additional change of magnetic entropy [2,4–7] Some remarkable anomalies in the vicinity of the magnetic ordering transition were also observed in a series of Cu-doped manganese oxides of La0.825Sr0.175Mn1ÀxCuxO3 (0.20 pxp0.40) [11] The study of MCE in such a Cudoped manganese perovskite can be, therefore, of great interest In the present work, the MCE in the La0.7Sr0.3Mn1ÀxCuxO3 (x ¼ 0:05; 0.10) polycrystalline perovskites is investigated It was found that the magnetic entropy change above 300 K is larger in the present Cu-doped manganites than that in gadolinium [9] The origin of the large magnetic entropy change is attributed to the abrupt reduction of magnetization which is associated with a first-order phase transition near the Curie temperature La0.7Sr0.3Mn1ÀxCuxO3 (x ¼ 0:05; 0.10) polycrystalline materials were prepared using a conventional powder solid-state reaction method Stoichiometric mixtures of La2O3, SrCO3, CuO and MnCO3 powders were used The samples were pre-sintered at 10001C for 15 h followed by grinding into compound powders The compound powders were then pressed into pellets and sintered at 12501C for 35 h to give the finished samples X-ray diffraction (Bruker D5005) confirmed the single-phase rhomboredral perovskite structure for both the compound powder and the finished samples The thermal stability associated with crystallization and melting was determined by differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA) (TA Instruments Apparatus SDT 2960) with a heating rate of 201C/ Magnetic measurements were performed using a Vibrating Sample Magnetometer in magnetic fields up to 19 kOe Fig shows the temperature dependences of the magnetization of the La0.7Sr0.3Mn0.9Cu0.1O3 (x=0.10) sample measured in the fields of 100 Oe and kOe (the insert of Fig 1) The Curie temperature (TC), defined by the maximum in the ‘‘absolute value’’ of dM/dT, has been determined from the M–T curve and found to be $347 and $349 K at H=100 Oe and kOe, respectively It is noted that, at H=5 kOe, the shape of the M–T curve remains almost unchanged, while the TC is shifted to a higher temperature (349 K) Similar Fig Temperature dependence of the magnezation for the La0.7Sr0.3Mn0.9Cu0.1O3 sample in the fields of 100 Oe and kOe (in the insert) behavior was observed for the La0.7Sr0.3Mn0.95 Cu0.05O3 (x=0.05) sample As reported in Ref [12], the MCE material MnAs0.9Sb0.1 exhibited a smooth temperature variation of the magnetization under high fields whereas the shape of the M–T curve for MnAs was almost unchanged, except the increase of the magnitude of magnetization and the shift of TC to higher temperature Consequently, MnAs was found to exhibit a larger magneto-caloric effect than MnAs1ÀxSbx [12] For the present Cu-doped manganites, the considerable increase of magnetization observed in H=5 kOe is consistent with the result that had been reported on other MCE materials, such as La0.8Ca0.2MnO3 polycrystalline perovskite [2] and La1.4Ca1.6Mn2O7 layered perovskite [13] Therefore, the La0.7Sr0.3Mn1ÀxCuxO3 (x ¼ 0:05; 0.10) materials in the present study are expected to exhibit large MCE near the Curie temperature In order to confirm this, the isothermal magnetization of both x ¼ 0:05 and 0.10 samples were measured with a field step of 500 Oe in a range of 0–19 kOe and a temperature interval of K in a temperature range of 100–380 K It is reasonable to consider the magnetization curves to be isothermal due to the sufficiently low sweeping rate of the magnetic field adopted during the experiment To ensure the readability of the figure, ARTICLE IN PRESS M.-H Phan et al / Journal of Magnetism and Magnetic Materials 285 (2005) 199–203 only twelve of them are presented in Fig including all the results obtained near the TC It can be seen clearly from Fig that there is a drastic change of the magnetization around the TC, indicating a large magnetic entropy change This coincides with the rapid reduction of magnetization at the TC (Fig 1) Another feature to be noted is that a large proportion of changes of the magnetization occurs in a relative low-field range (o19 kOe), which is beneficial for the household application of MCE materials [14] In order to evaluate the MCE of the present materials, we calculated changes of the magnetic entropy (DSM ) caused by the application of external magnetic fields from the isothermal curves of magnetization versus the applied field by using the following expression [1] X M i À M iỵ1 jDS M j ẳ DH i ; 1ị T iỵ1 T i i where Mi and Mi+1 are the magnetization values measured at temperatures Ti and Ti+1 in a field H, respectively In Fig 3, the magnetic entropy change (DSM ) is plotted against temperature (T) for x ¼ 0:10 composition at DH ¼ 10; 15 and 19 kOe Upon 10 kOe applied field, the highest value of $3.24 J/kg K for DSM was found at a temperature of $347 K ($TC) For comparison, in Table 1, we summarize the TC and DSM of different magnetic materials which could be Fig Magnetic field dependence of magnetization at various temperature around TC for the La0.7Sr0.3Mn0.9Cu0.1O3 sample 201 Fig The magnetic entropy change ðÀDSM Þ as a function of temperature in various magnetic fields for La0.7Sr0.3Mn0.9 Cu0.1O3 potentially used as magnetic refrigerants in magnetic refrigerators The MCE is clearly larger in the present Cu-doped manganites compared with that in gadolinium [9] and several other manganese oxides [1–7] For the same applied field, H ¼ 10 kOe, the maximum DS M of the Cu-doped samples is estimated to be $3.05 J/kg K for x ¼ 0:05 composition and $3.24 J/kg K for x ¼ 0:10 composition, while it is only $2.8 J/kg K for Gd metal [9] More interestingly, the large magnetic entropy changes in both samples were observed at a temperature above 300 K This allows the water to be used as a heat transfer fluid in the roomtemperature magnetic refrigeration regime [15] In addition, compared with gadolinium and its compounds [9,10], the polycrystalline Cu-doped manganese perovskite materials are easier to fabricate and possessing a higher chemical stability as well as a higher resistivity The high resistivity is beneficial to lowering the eddy current heating All these characteristics make the polycrystalline Cudoped manganese a competitive material for the room-temperature magnetic-refrigeration applications In general, the large magnetic entropy change in perovskite manganites mainly results from the considerable variation of magnetization near TC In addition, the spin-lattice coupling in the magnetic ordering process also plays an important role [2] Due to strong coupling between spin and lattice, significant lattice change accompanying ARTICLE IN PRESS 202 M.-H Phan et al / Journal of Magnetism and Magnetic Materials 285 (2005) 199–203 Table for different materials Curie temperature TC and the maximum magnetic entropy change DSmax M Material DH (kOe) TC max DS (J/kg K) M Reference La0.67Ca0.33MnOd La0.8Ag0.2MnO3 La0.7Ba0.12Ca0.18MnO3 La0.7Ca0.3MnO3 Gd La0.7Sr0.3Mn0.95Cu0.05O3 La0.7Sr0.3Mn0.95Cu0.1O3 La0.8Ca0.2MnO3 La0.67Ca0.33MnO3 La0.55Ca0.45MnO3 La0.7Sr0.3Mn0.95Cu0.05O3 La0.7Sr0.3Mn0.9Cu0.1O3 10 10 10 10 10 10 10 15 15 15 15 15 260 278 298 227 294 345 347 230 262 234 346 348 1.2 3.4 1.85 1.95 2.8 3.05 3.24 5.5 4.3 5.2 5.51 [1] [5] [7] [8] [9] Present Present [2] [2] [2] Present Present magnetic transition in perovskite manganites has been observed [2,16] The lattice structural change in the hMn2Oi bond distance as well as the hMn2O2Mni bond angle would, in turn, favor the spin ordering Thereby, a more abrupt reduction of magnetization near TC occurs and results in a significant magnetic-entropy change [1–7] In this way, a conclusion might be drawn that a strong spin-lattice coupling in the magnetic transition process would lead to additional magnetic entropy change near TC, and consequently, enhances the MCE In the present work, the observation of an endothermic peak of $348 K on the DSC curves of both the samples indicates that there exists a firstorder phase transition in these samples [5] Furthermore, it should be noted that most of the MCE materials were found to undergo a firstorder magnetic transition [9,10,12,17] As reported in Ref [17], the magnetic entropy change (DSM ) around the first-order transition was about three times larger than that obtained around the secondorder transition in the compound of Nd0.5Sr0.5MnO3 Similarly, the drop of MCE related to the change from first-order to secondorder magnetic phase transition was observed in La2/3(Ca1ÀxSrx)1/3MnO3 perovskites with increasing Sr-doped content [18] Consequently, it would not be too unreasonable to suggest the large magnetic entropy in the present Cu-doped manganites might be connected with the abrupt reduction in magnetization [17–20] The additional work work work work Fig The M–H curves obtained for the La0.7Sr0.3Mn1Àx CuxO3 (x ¼ 0:05; 0:1) samples entropy change can be attributed to the fact that the magnetic transition greatly enhances the effect of the applied magnetic field That is also the reason why a sharp magnetic phase transition retains almost unchanged even under high fields It is therefore proposed that the partial substitution of Cu for Mn in the La0.7Sr0.3Mn1ÀxCuxO3 perovskites would favor a soft ferromagnetic character (see Fig 4) It is noteworthy that the present Cu-doped samples exhibited a relatively small magnetic hysteresis with coercivity of $40 Oe near TC (T ¼ 340 K), which is beneficial to the magnetic cooling efficiency [15,20] In summary, the magnetocaloric effect in the La0.7Sr0.3Mn1ÀxCuxO3 (x ¼ 0:05; 0.10) materials ARTICLE IN PRESS M.-H Phan et al / Journal of Magnetism and Magnetic Materials 285 (2005) 199–203 is studied A larger magnetic entropy change than that of gadolinium has been observed in the Cudoped manganites This, together with the other ideal MCE behaviors, makes these materials possible for the room-temperature magnetic-refrigeration applications The large magnetic entropy change, in the Cu-doped manganites, caused by the abrupt reduction of magnetization is associated with a first-order crystallographic phase transition near the Curie temperature Acknowledgements One of the authors (M.H Phan) would like to thank Professor F de Boer for helpful discussions Research at Chungbuk National University was supported by the Korea Research Foundation Grant No KRF-2001-005-D20010 Research at Center for Materials Science was supported by the Vietnam National Program for Fundamental Research Grant No 420110 References [1] X.X Zhang, J Tejada, Y Xin, G.F Sun, K.W Wong, Appl Phys Lett 69 (1996) 3596 [2] Z.B Guo, Y.W Du, J.S Zhu, H Huang, W.P Ding, D Feng, Appl Phys Lett 78 (1997) 1142 203 [3] X Bohigas, J Tejada, E del Barco, X.X Zhang, M Sales, Appl Phys Lett 73 (1998) 390 [4] Y Sun, X.J Xu, Y.H Zhang, J Magn Magn Mater 219 (2000) 183 [5] T Tang, K.M Gu, Q.Q Cao, D.H Wang, S.Y Zhang, Y.W Du, J Magn Magn Mater 222 (2000) 110 [6] Y Sun, W Tong, Y.H Zhang, J Magn Magn Mater 232 (2001) 205 [7] M.H Phan, S.B Tian, S.C Yu, A.N Ulyanov, J Magn Magn Mater 256 (2003) 306 [8] S.B Tian, M.H Phan, S.C Yu, N.H Hur, Physica B 327 (2003) 221 [9] S.Yu Dan’kov, A.M Tishin, V.K Pecharsky, K.A Gschneidner Jr., Phys Rev B 57 (1998) 3478 [10] V.K Pecharsky, K.A Gschneidner Jr., Phys Rev Lett 78 (1997) 4494 [11] L Pi, X.J Xu, Y.H Zhang, Phys Rev B 62 (2000) 5667 [12] H Wada, Y Tanabe, Appl Phys Lett 79 (2001) 3302 [13] H Zhu, H Song, Y.H Zhang, Appl Phys Lett 81 (2002) 3416 [14] V.K Pecharsky, K.A Gschneidner Jr., J Appl Phys 90 (2001) 4614 [15] V.K Pecharsky, K.A Gschneidner Jr., J Magn Magn Mater 200 (1999) 44 [16] P.G Radaelli, D.E Cox, M Marezio, S.W Cheong, P.E Schiffer, A.P Ramirez, Phys Rev Lett 75 (1995) 4488 [17] P Sande, L.E Hueso, D.R Miguens, J Rivas, F Rivadulla, M.A Lopez-Quintela, Appl Phys Lett 79 (2001) 2040 [18] J Mira, J Rivas, L.E Hueso, F Rivadulla, M.A Lopez Quintela, J Appl Phys 91 (2002) 8903 [19] D.H Ryan, Miryam, Elouneg-Jamroz, J van Lierop, H.B Wang, Phys Rev Lett 90 (2003) 117202 [20] Q Tegus, E Bruck, K.H.J Buschow, F.R de Boer, Nature 415 (2002) 150  ... the large magnetic entropy change in perovskite manganites mainly results from the considerable variation of magnetization near TC In addition, the spin-lattice coupling in the magnetic ordering... is larger in the present Cu-doped manganites than that in gadolinium [9] The origin of the large magnetic entropy change is attributed to the abrupt reduction of magnetization which is associated... presented in Fig including all the results obtained near the TC It can be seen clearly from Fig that there is a drastic change of the magnetization around the TC, indicating a large magnetic entropy change