DSpace at VNU: Large magnetic-entropy change above 300 K in CMR materials

Journal of Magnetism and Magnetic Materials 258–259 (2003) 309–311 Large magnetic-entropy change above 300 K in CMR materials M.H Phana,b, S.B Tiana, D.Q Hoanga, S.C Yua,*, C Nguyenb, A.N Ulyanova,c a Department of Physics, Chungbuk National University, Cheongju 361-763, South Korea Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Viet Nam c Donetsk Physico-Technical Institute of National Academy of Sciences, 83114 Donetsk, Ukraine b Abstract A large magnetic-entropy change DSM associated with the ferromagnetic–paramagnetic transition in CMR materials (La0.65Sr0.35MnO3, La0.6Sr0.2Ca0.2MnO3, La0.6Sr0.2Ba0.2MnO3 and La0.7Ca0.06Ba0.24MnO3) has been observed It is shown that the DSM reaches a maximum value of 2.26 J/kg/K for La0.6Sr0.2Ba0.2MnO3 composition at Curie temperature of 354 K, upon 10 kOe applied field variation Due to the large DSM and high Curie temperature, these CMR materials are suggested to use as active magnetic refrigerants for magnetic refrigeration technology above room temperature r 2002 Elsevier Science B.V All rights reserved Keywords: Entropy; Magnetocaloric effect; Magnetic refrigeration; Perovskite; Double exchange Magnetic cooling by the magnetocaloric (MC) effect has a long history First, in 1926 Debye [1] and in 1927 Giauque [2] predicted the theoretical possibility of adiabatic demagnetization cooling The MC effect is well known to be a large change of magnetic entropy closely related to that of the temperature of an adiabatically isolated system caused by variation of an external magnetic field In recent years, Pecharsky and Gschneidner [3] discovered a giant magnetic-entropy change associated with the transition temperature (TC ) in Gd metal and then in Gd5Si2Ge2 alloy The last compound exhibits an MC effect about twice as large as that exhibited by gadolinium, the best known magnetic refrigerant material for near room temperature applications However, the purpose in searching a proper material with the large magnetic-entropy change and its possibility of various temperature-ranges application is always required Rare-earth perovskite manganites of the general formula La1ÀxMxMnO3 (M=Ca, Sr, Ba, etc.) *Corresponding author Tel.: +82-431-261-2269; fax: +82-431-275-6416 E-mail address: scyu@chungbuk.ac.kr (S.C Yu) have attracted much attention because of their higher potential for magnetic sensor applications based on the magnetoresistance effect [4,5] Additionally, these materials are very convenient for the preparation routes, and their Curie temperature can be justified under the various doping conditions Therefore, the new trends have been focusing on studying the MC effect of perovskite manganites [6–8] Due to the large magnetic-entropy change, they have been widely used for magnetic refrigeration applications in different temperature ranges In this paper, we present a study of the MC effect in CMR materials (La0.65Sr0.35MnO3, La0.6Sr0.2Ca0.2MnO3, La0.6Sr0.2Ba0.2MnO3 and La0.7Ca0.06Ba0.24MnO3) La0.65Sr0.35MnO3 (No 1), La0.6Sr0.2Ca0.2MnO3 (No 2), La0.6Sr0.2Ba0.2MnO3 (No 3) and La0.7Ca0.06Ba0.24MnO3 (No 4) samples were prepared by the conventional solid-state reaction technique from a stoichiometric mixture of La2O3, SrCO3, CaCO3, BaCO3 and MnO2 at a pre-sintering temperature of 12501C for 16 h They were sintered at 13501C for 18 h after regrinding and pressing for pellets The samples were examined by the X-ray diffraction and showed the single-phase rhombohedral perovskite structure The magnetic 0304-8853/03/$ - see front matter r 2002 Elsevier Science B.V All rights reserved PII: S - 8 ( ) 1 - M.H Phan et al / Journal of Magnetism and Magnetic Materials 258–259 (2003) 309–311 310 characteristics were performed with a vibrating sample magnetometer (VSM) in the fields up to 10 kOe Fig shows the temperature-dependent magnetization for a selected sample (No 3), where its Curie temperature of 354 K was obtained The Curie temperature TC ; defined as the temperature at which the qM=qT2T curve reaches a minimum, has been determined from the M2T curves The TC of the samples was summarized in Table In Fig 2, the magnetic fielddependent magnetization curves of No show a strong variation of magnetization around the Curie temperature It means that a large magnetic-entropy variation associated with the ferromagnetic–paramagnetic transition temperature (TC ) can be made to result; it will be discussed later According to the thermodynamic theory, the magnetic-entropy change caused by the variation of the magnetic field from to Hmax is given by [3]  Z Hmax  qM dH: 1ị DSM ẳ qT H Based on expression (1) the magnetic-entropy changes as a function of temperature for the samples 1–4 at the external magnetic fields of 10 kOe were calculated and plotted in Fig Large magnetic-entropy changes max (jDSM j) are reported for all the samples and they are summarized in Table Among the investigated samples, La0.6Sr0.2Ba0.2MnO3 (No 3) exhibits a highest 14 1.8 12 FC 210 K La0.6Sr0.2Ba0.2MnO3 (No 3) 10 H = 50 Oe 1.5 M (emu/g) ZFC M (arb units) La0.6Sr0.2Ba0.2MnO3 (No 3) 1.2 0.9 0.6 0.3 0.0 100 150 200 250 300 T (K) 350 400 Fig Temperature-dependent magnetization taken both zerofield-cooled (ZFC) and field-cooled (FC) at 50 Oe for a selected sample of La0.6Sr0.2Ba0.2MnO3 (No 3) 410 K 450 2000 4000 6000 8000 10000 H (Oe) Fig Magnetic field dependence of the magnetization for La0.6Sr0.2Ba0.2MnO3 (No 3) at temperatures from 210 to 410 K (DT ¼ 10 K) Table max Curie temperature TC and the maximum magnetic entropy change, jDSM j; for different compositions Composition TC (K) max jDSM j (J/kg/K) DH (T) Reference La0.6Ca0.4MnO3 La0.65Ca0.35Mn0.9Ti0.1O3 La0.958Li0.025Mn0.9Ti0.1O3 La0.65Sr0.35MnO3 La0.6Sr0.2Ca0.2MnO3 La0.6Sr0.2Ba0.2MnO3 La0.7Ca0.06Ba0.24MnO3 La0.65Nd0.05Ca0.3MnO3 La0.65Nd0.05Ca0.3Mn0.9Cr0.1O3 La0.65Nd0.05Ca0.3Mn0.9Fe0.1O3 Gd Gd5(Si2Ge2)a Gd5(Si2Ge2)b 263 103 90 305 337 354 320 250 220 130 294 276 300 5.0 1.3 2.0 2.12 1.96 2.26 1.72 1.68 0.96 0.42 4.2 14 3 1 1 1 1.5 [6] [6] [6] Present Present Present Present [8] [8] [8] [3] [3] [3] a b Prepared using high-purity Gd (B99.8 at% pure) Prepared using commercial purity Gd (95–98 at% pure) work work work work M.H Phan et al / Journal of Magnetism and Magnetic Materials 258–259 (2003) 309–311 2.5 -∆SM (J/kg/K) 2.0 No No No No 1.5 1.0 0.5 0.0 210 240 270 300 330 360 390 420 450 T (K) Fig The magnetic-entropy change as a function of temperature for the samples (La0.65Sr0.35MnO3 (No 1), La0.6Sr0.2Ca0.2MnO3 (No 2), La0.6Sr0.2Ba0.2MnO3 (No 3) and La0.7Ca0.06Ba0.24MnO3 (No 4)) upon a 10 kOe field variation max value of 2.26 J/kg/K for jDSM j at the Curie temperature of 354 K These results indicate that the present investigated samples are very good substances for magnetic refrigeration applications A large magneticentropy variation in perovskite manganites has been almost interpreted in terms of the double-exchange model [9] It has been believed to relate closely to the mechanism of double-exchange interaction between Mn3+ and Mn4+ ions arising from the change in the Mn4+/Mn3+ ratio, under the doping process [7,8,10] For our circumstance, the partial replacement of La with Sr or (Ba,Ca) could enhance the double-exchange interaction due to the increase of the Mn4+/Mn3+ ratio, and thus result in the large magnetic-entropy change Additionally, Guo et al [11] indicated that the large magnetic-entropy change in perovskite manganites could originate from the spin–lattice coupling in the magnetic ordering process Since the strong coupling between spin and lattice, the significant lattice change accompanying magnetic transition in perovskite manganites has been observed [12] The lattice structural change in the /Mn2OS bond distance as well as /Mn2O2MnS bond angle would in turn favor the spin ordering Thus, a more abrupt variation of magnetization near TC occurred, resulting in a large magnetic-entropy change as the large MC effect For comparison, the data of several magnetic materials, which could be used as active refrigerants, are summarized in Table As follows from the table, though the max values of jDSM j are smaller than the most conspicuous 311 MC material Gd5(Si2Ge2), these perovskite manganites are easy to fabricate and exhibit higher chemical stability as well as higher resistivity which is favorable for the lowering of eddy current heating Besides, it is possible to adjust the Curie temperature of perovskite manganites by either A- or B-site doping, and consequently, a large magnetic-entropy change can be tuned from low temperature to near or above room temperature, which is beneficial for operating magnetic refrigeration at various temperature ranges In conclusion, a large MC effect in CMR materials (La0.65Sr0.35MnO3, La0.6Sr0.2Ca0.2MnO3, La0.6Sr0.2Ba0.2MnO3 and La0.7Ca0.06Ba0.24MnO3) with Curie temperatures above 300 K has been found La0.6Sr0.2Ba0.2MnO3 exhibits the highest value of 2.26 J/kg/K for max jat the Curie temperature of 354 K, upon 10 kOe jDSM applied field variation The increasing of the Mn4+/ Mn3+ ratio leads to an enhancement in the doubleexchange interaction of Mn3+and Mn4+ ions, which results in a large magnetic-entropy variation A combination of both the large magnetic-entropy change and high Curie temperature makes CMR materials appropriate substances for magnetic refrigeration applications above room temperature Research at Korea was supported by the Korean Research Foundation Grant (KRF-2001-005-D20010) References [1] P Debye, Ann Phys 81 (1926) 1154 [2] W.F Giauque, J Am Chem Soc 49 (1927) 1870 [3] V.K Pecharsky, K.A Gschneidner Jr., Phys Rev Lett 78 (1997) 4494 [4] R von Helmolt, J Wecker, B Holzapfel, L Schultz, K Samwer, Phys Rev Lett 71 (1993) 2331 [5] G.A Prinz, J Magn Magn Mater 200 (1999) 57 [6] X Bohigas, J Tejada, E Del Barco, X.X Zhang, M Sales, Appl Phys Lett 73 (1998) 390 [7] Y Sun, X Xu, Y Zhang, J Magn Magn Mater 219 (2000) 183 [8] Z.M Wang, G Ni, Q.Y Xu, H Sang, Y.W Du, J Magn Magn Mater 234 (2001) 371 [9] C Zener, Phys Rev 81 (1951) 440; C Zener, Phys Rev 82 (1955) 403 [10] Y Sun, W Tong, Y Zhang, J Magn Magn Mater 232 (2001) 205 [11] Z.B Guo, Y.M Du, J.S Zhu, H Huang, W.P Ding, D Feng, Phys Rev Lett 78 (1997) 1142 [12] P.G Radaelli, D.E Cox, M Marezio, S.W Cheong, P.E Schiffer, A.P Ramirez, Phys Rev Lett 75 (1995) 4488  ... change in perovskite manganites could originate from the spin–lattice coupling in the magnetic ordering process Since the strong coupling between spin and lattice, the significant lattice change. .. double-exchange interaction due to the increase of the Mn4+/Mn3+ ratio, and thus result in the large magnetic-entropy change Additionally, Guo et al [11] indicated that the large magnetic-entropy change. .. from low temperature to near or above room temperature, which is beneficial for operating magnetic refrigeration at various temperature ranges In conclusion, a large MC effect in CMR materials (La0.65Sr0.35MnO3,