1352 IEEE TRANSACTIONS ON MAGNETICS, VOL. 48, NO. 4, APRIL 2012 The Variation of Magnetic Entropy on Compound With the Sintering Temperature Kyeong-Sup Kim , Seong-Cho Yu , Byung-Sub Kang , Peng Zhang , Dong-Hyun Kim , and Suhk-Kun Oh Department of Physics and BK21 Physical Program, Chungbuk National University, Cheongju 361-763, South Korea Department of Nano Science and Mechanical Engineering, Konkuk University, Chungju 380-701, South Korea The magnetic entropy behavior has been analyzed in the double-perovskite ( , 0.1, 0.2) compound with the sintering temperature. Samples were fabricated by conventional solid-state reaction method. The results show that the values of are increased with increasing sintering temperature from 1273 K to 1473 K. The values of for are increased about five times with increasing sintering temperature, especially. The enhancement of the magnetic entropy change is believed to be due to a strong coupling between spin and lattice in the magnetic transition process near Curie temperature. Our result reveals that the proper sintering of perovskite compound makes it one of the useful methods for the development of advanced magnetic refrigeration materials. Index Terms—Magnetic entropy, magnetization, magnetocaloric effect. I. INTRODUCTION T HE magnetic caloric effect (MCE) is induced via the coupling of the magnetic sub-lattice with the magnetic field, which alters the magnetic part of the total entropy due to a corresponding change in the magnetic field. Traditionally, di- luted paramagnetic slats and rare earth intermetallic compounds that display significant MCE have been considered as attractive materials for cryogenic applications [1], [2]. Especially, double perovskite (BFMO) shows room temperature magnetoresistance and a ferrimagnetic phase transition with a Curie temperature of 310 330 K [3], [4]. Therefore, it would be very interesting to study the magnetocaloric effect for these materials because of the Curie temperature being near room temperature. We have recently published reports on the mag- netocaloric effect of compound with sintering temperature [5]. We show that magnetic entropy change can be tuned by suitable sintering process. The values of were increased about two times with increasing sintering temperature from 1273 to 1473 K. In this work, the magnetocaloric effect of ( , 0.1, 0.2) compound with the sintering temperature was investigated. Materials with proper Curie temperature and large magnetic entropy change have many interesting properties that are attractive for applications as magnetic refrigerants. II. EXPERIMENTS Polycrystalline (BLFMO) samples were prepared by standard solid-state reaction in a stream of 5% gas at various sintering temperatures of 1273 K, 1373 K, and 1473 K for 5 h. A stoichiometric mixture of high purity (99.99%), (99.99%), (99.99%), and (99.99%) powders were fired in an crucible at 1173 K in an electric furnace. X-ray diffraction patterns were taken with a Phillips diffractometer using radi- Manuscript received August 14, 2011; accepted September 30, 2011. Date of current version March 23, 2012. Corresponding author: S.-C. Yu (e-mail: scyu@chungbuk.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2011.2172588 ation. The temperature dependence of the magnetization was measured with a commercial vibrating sample magnetometer (VSM) at various temperatures from 300 K to 400 K in fields up to 15 kOe. III. RESULTS AND DISCUSSION The perovskite-like structured materials have generated con- siderable attention in the domain of magnetic sensors physics, which is based on the colossal magneto-resistance effect, and in magnetic refrigerators making using of the magnetocaloric effect. The magnetocaloric effect can be measured directly or it can be indirectly from the measured magnetization. Magne- tization measured experimentally as a function of temperature has been rightfully suggested as a useful technique. The mag- netic entropy change is caused by the variation of the external magnetic field. On the basis of the thermodynamic theory, the magnetic entropy change caused by the variation of the external magnetic field from 0 to is given by (1) From the Maxwell’s thermodynamic relationship (2) Equation (1) can be rewritten as follows: (3) Numerical evaluation of the magnetic entropy change was carried out from formula (3) using isothermal magnetization measurements at small discrete field and temperature intervals, can be computed approximately from (3) by (4) where and are the magnetization values measured at temperature and in a field , respectively. Thus, the 0018-9464/$31.00 © 2012 IEEE