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1200-G07-04

Comparative Study of the Magnetocaloric Properties in Ni-Mn-X (X = Ga, In, Sn) by Magnetization and Specific Heat Measurements V. V. Khovaylo1, K. P. Skokov2,3, E. V. Avilova1, V. Novosad4, H. Miki5, R. Kainuma6, G. Wang7, E. Palacios7, J. Bartolomé7, and R. Burriel7 1 National University of Science and Technology “MISiS”, Leninsky av., 4, Moscow 119049, Russia 2 Faculty of Physics, Tver State University, Tver 170000, Russia 3 Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden), Institute for Metallic Materials, P.O. Box 270016, D-01171 Dresden, Germany 4 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA 5 Institute of Fluid Science, Tohoku University, Katahira 1-1-2, Aoba-ku, Sendai 980-8577, Japan 6 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 1-1-2, Aoba-ku, Sendai 980-8577, Japan 7 Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada (CSIC - Universidad de Zaragoza), Zaragoza 50009, Spain ABSTRACT Some compositions of Ni-Mn-X (X = Ga, In, Sn) ferromagnetic shape memory alloys exhibit a first order magnetostructural phase transition. Magnetic entropy change ∆Sm in the vicinity of this transition has been studied by magnetization and heat capacity measurements. Comparison of these results point to a large difference in magnitudes of ∆Sm obtained from magnetization and heat capacity data. It is suggested that this discrepancy originates from overestimation of ∆Sm determined from the magnetization measurements and underestimation of ∆Sm obtained from the heat capacity measurements. INTRODUCTION Recently, a considerable interest has been paid to magnetocaloric properties of ferromagnetic shape memory alloys Ni-Mn-X (X = Ga, Sn, In, Sb) [1]. Due to the difference in exchange interactions of the parent austenitic phase and the product martensitic phase, a peculiar transformation sequence from paramagnetic low-temperature phase to a ferromagnetic hightemperature phase can be realized in Ni-Mn-X (X = Sn, In) alloys of certain chemical compositions [2,3]. In the Ni-Mn-Ga system, the magnetostructural phase transition takes place from ferromagnetic martensitic phase to paramagnetic austenitic phase [4]. These coupled magnetostructural phase transitions are reversible on subsequent cooling and shows rather a small (6 – 10 K) temperature hysteresis. Reported values of the isothermal magnetic entropy change ∆Sm accompanying these first-order phase transitions [5-12] imply that |∆Sm| is

comparable to or exceeds that of Gd5(Si1-xGex), La(Fe1-xSix)13, and other related compound demonstrating giant magnetocaloric effect [13]. Judging by these reports, Ni-Mn-X are perspective materials for the use in the technology of room-temperature magnetic refrigeration. Most of the papers devoted to the magnetocaloric effect of these alloys report on the magnetic entropy change ∆Sm calculated from magnetization measurements. Judging by a large scatter in ∆Sm reported for the same co