Journal of Magnetism and Magnetic Materials 290–291 (2005) 669–672 Effect of hydrostatic pressure on magnetization of Ni 2+x Mn 1x Ga alloys J. Kamara´ d à , F. Albertini, Z. Arnold, F. Casoli, L. Pareti, A. Paoluzi a Institute of Physics AS CR, Na Slovance 2, 182 21 Praha 8, Czech Republic b IMEM-CNR, Parco Area delle Scienze, Fontanini, 43010 Parma, Italy Available online 14 December 2004 Abstract The effect of pressures up to 1.2 GPa on saturated magnetization M S of Ni 2+x Mn 1x Ga (0pxp0.2) alloys has been studied at temperatures from 5 to 400 K. The pressure parameter, dln M S /dp at 5 K, varies from 0.3  10 2 GPa 1 up to 1.3  10 2 GPa 1 . At temperature T M of martensitic transition (MT), dln M S /dp changes its sign. M S and the Curie temperature T C of the cubic phase of compounds increase with increasing pressure. These results are consistent with a theoretical picture of band structure of Ni 2 MnGa assuming a broadening and a depletion of the dominant minority Ni e g band under pressure. r 2004 Elsevier B.V. All rights reserved. PACS: 75.30.Cr; 75.50.Cc Keywords: Magnetization–pressure dependent; Heusler alloys; Pressure effect 1. Introduction Great attention is paid to the study of shape-memory and magnetocaloric effects in the Ni–Mn–Ga Heusler alloys with martensitic transition (MT) between a high- temperature cubic phase and a low-temperature phase of lower symmetry (tetragonal, orthorombic or monocli- nic, depending on stoichiometry) [1,2]. The significant magnetocaloric effect observed in these alloys is caused by a pronounced change of magnetization at MT that has its origin on an atomic level [3,4]. MT in the alloys can be cycled without their destruction, so a possibility to produce giant strains by magnetic fields in these materials [5,6] attracts practical interest. However, residual stress–strain phenomena at the mesoscopic level induced by reversal MT can affect the useful features of the alloys. In this paper, the effect of external hydro- static pressure on saturated and low-field magnetization of Ni 2+x Mn 1x Ga (0pxp0.2) Heusler alloys has been studied to analyse the magnetovolume effects on both atomic and mesoscopic length levels. The polycrystalline stoichiometric Ni 2 MnGa (Ni00) alloy and the Ni 2+x Mn 1x Ga alloys with x ¼ 0:15 (Ni15), x ¼ 0:18 (Ni18) and x ¼ 0:20 (Ni20) were prepared by a standard arc melting with a subsequent homogenization, see Ref. [6]. A test of resulting compositions of the alloys by a micro-probe verified their excellent homogeneity with a low lack of Ga (1.5 at%) with respect to their nominal composition. The samples were compressed in a liquid pressure medium in a non-magnetic high-pressure CuBe cell by hydrostatic pressures [7]. Magnetization of the alloys (in the miniature CuBe cell) was measured in fields up to 5 T ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.11.332 à Corresponding author. Institute of Physics AS CR, Cukrovarnicka´ 10, 162 53 Praha 6, Czech Republic. Tel.: +420 220318521; fax: +420 233343184. E-mail address: kamarad@fzu.cz (J. Kamara´d).