Chinese Physics B ( First Published in 1992 )

Chinese Physics B ( First published in 1992 ) Published monthly in hard copy by the Chinese Physical Society and online by IOP Publishing, Temple Circus, Temple Way, Bristol BS1 6HG, UK Institutional subscription information: 2013 volume For all countries, except the United States, Canada and Central and South America, the subscription rate is $977 per annual volume. Single-issue price $97. Delivery is by air-speeded mail from the United Kingdom. Orders to: Journals Subscription Fulfilment, IOP Publishing, Temple Circus, Temple Way, Bristol BS1 6HG, UK For the United States, Canada and Central and South America, the subscription rate is US$1930 per annual volume. Single-issue price US$194. Delivery is by transatlantic airfreight and onward mailing. Orders to: IOP Publishing, PO Box 320, Congers, NY 10920-0320, USA ⃝c 2013 Chinese Physical Society and IOP Publishing Ltd All rights reserved. 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Supported by the National Natural Science Foundation of China, the China Association for Science and Technology, and the Science Publication Foundation, Chinese Academy of Sciences Editorial Office: Institute of Physics, Chinese Academy of Sciences, PO Box 603, Beijing 100190, China Tel: (86 { 10) 82649026 or 82649519, Fax: (86 { 10) 82649027, E-mail: [email protected] 主管单位: 中国科学院国内统一刊号: CN 11{5639/O4 主办单位: 中国物理学会和中国科学院物理研究所广告经营许可证：京海工商广字第0335号承办单位: 中国科学院物理研究所编辑部地址: 北京中关村中国科学院物理研究所内主编：欧阳钟灿通讯地址: 100190 北京 603 信箱出版：中国物理学会 Chinese Physics B 编辑部印刷装订：北京科信印刷厂电话: (010) 82649026, 82649519 编辑: Chinese Physics B 编辑部传真: (010) 82649027 国内发行: Chinese Physics B 出版发行部 E-mail: [email protected] 国外发行: IOP Publishing Ltd \Chinese Physics B"网址: 发行范围: 公开发行 http://cpb.iphy.ac.cn(编辑部) 国际统一刊号: ISSN 1674{1056 http://iopscience.iop.org/cpb (IOP) Published by the Chinese Physical Society 顾顾顾问问问 Advisory Board 陈佳洱教授, 院士 Prof. Academician Chen Jia-Er 北京大学物理学院, 北京 100871 School of Physics, Peking University, Beijing 100871, China 冯端教授, 院士 Prof. Academician Feng Duan 南京大学物理系, 南京 210093 Department of Physics, Nanjing University, Nanjing 210093, China 黄祖洽教授, 院士 Prof. Academician Huang Zu-Qia 北京师范大学低能核物理研究所, Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 北京 100875 100875, China 李政道教授, 院士 Prof. Academician T. D. Lee Department of Physics, Columbia University, New York, NY 10027, USA 李荫远研究员, 院士 Prof. Academician Li Yin-Yuan 中国科学院物理研究所, 北京 100190 Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 丁肇中教授, 院士 Prof. Academician Samuel C. C. Ting LEP3, CERN, CH-1211, Geneva 23, Switzerland 杨振宁教授, 院士 Prof. Academician C. N. Yang Institute for Theoretical Physics, State University of New York, USA 杨福家教授, 院士 Prof. Academician Yang Fu-Jia 复旦大学物理二系, 上海 200433 Department of Nuclear Physics, Fudan University, Shanghai 200433, China 周光召研究员, 院士 Prof. Academician Zhou Guang-Zhao (Chou Kuang-Chao) 中国科学技术协会, 北京 100863 China Association for Science and Technology, Beijing 100863, China 王乃彦研究员, 院士 Prof. Academician Wang Nai-Yan 中国原子能科学研究院, 北京 102413 China Institute of Atomic Energy, Beijing 102413, China 梁敬魁研究员, 院士 Prof. Academician Liang Jing-Kui 中国科学院物理研究所, 北京 100190 Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China (Continued ) Chin. Phys. B Vol. 22, No. 5 (2013) 057502 ∗ Large reversible magnetocaloric effect in HoMn2O5 Ge Heng(葛恒)a)b), Zhang Xiang-Qun(张向群)b), Ke Ya-Jiao(柯亚娇)b), Jin Jin-Ling(靳金玲)b), Liao Zhi-Xin(廖志新)a), and Cheng Zhao-Hua(成昭华)b)† a)School of Chemistry and Chemical Engineering, Southeast University, Nanjing 210009, China b)State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China (Received 25 November 2012; revised manuscript received 10 January 2013) Magnetocaloric effect (MCE) in polycrystalline HoMn2O5 was investigated by isothermal magnetization curves from 2 K to 50 K. A relatively large magnetic entropy change, DSM = 7:8 J/(kg·K), was achieved with the magnetic field up to 70 kOe (1 Oe = 79:5775 A · m−1). The magnetic entropy change is reversible in the whole range of temperature. The contributions of elastic and magnetoelastic energy to the changing of the magnetic entropy are discussed in terms of the Landau theory. The reversibility of MCE with maximal refrigerant capacity RC = 216:7 J/kg makes polycrystalline HoMn2O5 promising as a magnetic refrigerant. Keywords: HoMn2O5, magnetocaloric effect PACS: 75.47.Lx, 75.30.Sg DOI: 10.1088/1674-1056/22/5/057502 1. Introduction rial. Its magnetostriction effect[12,13] and the magnetoelectric [14–18] Magnetic refrigeration, based on the magnetocaloric ef- coupling effect have been studied extensively. The exter- fect (MCE), has attracted wide interest because of its high nal magnetic field can induce and/or modify the ferroelectric energy efficiency and environment-friendliness. It is mean- states in RMn2O5 (R = Dy, Ho, etc.). [12,13] ingful to explore prominent refrigerants for different work- Its magnetostriction effect, especially the magne- [14–18] ing temperature ranges with larger entropy change and lit- toelectric coupling effect, in which an external mag- tle hysteresis of both the temperature and the magnetic field. netic field induces and/or modifies the ferroelectric states in RMn2O5 (R = Dy, Ho, etc), has been studied extensively. RMn2O5 (R represents the rare earth element) is orthorhom- Under an external magnetic field, the complicated mag- bic, has Pbam space group symmetry,[1] and it contains infinite 4+ netic structure results in complicated magnetic phases. Al- chains of Mn O6 octahedra sharing edges, linked together by 3+ [2,3] though the giant anisotropy of the magnetocaloric effect has Mn O5 and HoO8 units. The characteristic magnetic or- been studied in RMnO single crystals[19,20] with various spi- dering of the system exhibits a transition from incommensu- 3 ral magnetic structures, the effect of the complicated mag- rate to commensurate, and then to incommensurate antiferro- netic structure in RMn O on its MCE is not yet well under- magnetic (AFM) magnetic structure with the decrease of the 2 5 stood. In this paper, we focus on the MCE in a polycrystalline temperature.[4] For example, the past reports indicated that HoMn2O5 sample. HoMn2O5 displays a series of complicated phase transitions due to both the long range ordering of Ho3+ moments and the coexistence of Mn3+ and Mn4+. Long-range AFM ordering of 2. Experiment 3+ 4+ the Mn /Mn spins occurs at the temperature of TN = 43 K. The polycrystalline, single-phase sample HoMn2O5 was Subsequently, the ferroelectric (FE) transition takes place at synthesized through a standard solid-state reaction method. the temperature of TC= 39 K, slightly below TN. Another mag- Stoichiometric amounts of Ho2O3 (99.95%), MnO2 (99.9%) 0 netic transition occurs at the temperature of TN = 22:5 K, when were thoroughly mixed, compressed into pellets, and then sin- ◦ commensurate AFM ordering becomes incommensurate. Be- tered at the temperature of 1120 C for 48 h in O2 atmosphere. low 19 K, the phase transition from incommensurate AFM or- The sample was finally cooled down to room temperature. X- dering to canted AFM takes place and a second CAFM-type ray powder diffraction (XRD) patterns were collected with Cu [5–7] ordering of the Ho ions occurs at TN(Ho) below 10 K. Ka radiation in a Rigaku RINT 1400. The XRD patterns As a result, this type of manganese oxide shows many in- proved that the sample was in pure phase with a polycrystalline teresting physical characteristics in dielectric properties, spe- structure. The results were analyzed by Rietveld method with cial heat, and thermal expansion behaviors.[8–11] In addition, the Rietica program. Magnetization measurements were car- RMn2O5 has attracted wide interests as a multiferroic mate- ried out at a temperature ranging from 2 K to 300 K and mag- ∗Project supported by the National Basic Research Program of China (Grant Nos. 2010CB934202 and 2011CB921801) and the National Natural Science Foundation of China (Grant Nos. 11174351 and 11274360). †Corresponding author. E-mail: [email protected] © 2013 Chinese Physical Society and IOP Publishing Ltd http://iopscience.iop.org/cpb http://cpb.iphy.ac.cn 057502-1 Chin. Phys. B Vol. 22, No. 5 (2013) 057502 netic field up to 70 kOe with a commercial superconducting no hysteresis of either the temperature or the magnetic field quantum interference device (SQUID) magnetometer (Quan- appears in the vicinity of a magnetic ordering temperature.[21] tum design, MPMS-XL). There is almost no hysteresis of either temperature or magnetic field, as shown by the curves. The magnetic entropy change 3. Results and discussion DSM produced by the variation of external magnetic field from 0 to H can be calculated by[22] Figure1 shows the X-ray diffraction (XRD) patterns of HoMn O at room temperature and the fitted results. The Z H ¶M 2 5 DS(T;H) = S(T;H) − S(T;0) = dH crosses and the red solid line represent the observed data 0 ¶T H points and the Rietveld refinement patterns, respectively. The H M j − M j = T+DT T−DT DH; (1) vertical marks show the positions of Bragg diffraction. The ∑ 0 (T + DT) − (T − DT) H green line means the difference between the observed and cal- where DT = 1 K and DH = 2 kOe. The calculated −DS is culated intensities. The XRD patterns suggest that the sam- M shown as black dots in Fig. 4, and the peak of the magnetic ple is in pure phase with Pbam symmetry. The lattice pa- entropy change appears below 17 K under different magnetic rameters, a = 7:2723 A,˚ b = 8:4682 A,˚ and c = 5:6667 A,˚ fields.

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