Cryst. Res. Technol. 47, No. 3, 341 – 346 (2012) / DOI 10.1002/crat.201100485 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Magnetocaloric effect in GdCu intermetallic compound M. Oboz*, E. Talik, and A. Winiarski Institiute of Physics, University of Silesia, Uniwersytecka 4, 40007 Katowice, Poland Received 14 October 2011, revised 15 November 2011, accepted 24 November 2011 Published online 16 December 2011 Key words rare-earth intermetallics, Czochralski method, magnetic properties, magnetocaloric effect. A single crystal of GdCu of FeB-type was grown by the Czochralski method from a levitating melt and characterized using X-ray diffraction, dc-magnetization M(T) and ac-magnetic susceptibility (ac-χ). From ac and dc magnetic susceptibility a transition to the antiferromagnetic state has been found below T N = 37 K. The paramagnetic Curie temperature θ p and the effective magnetic moment μ eff were estimated assuming the Curie-Weiss law in the 100 to 300 K range and were found to be θ p = -37 K and μ eff = 8.5 μ B . The last value is enhanced relatively to the free ion value of 7.94 μ B for Gd 3+ . The calculated entropy changes ΔS m for the examined compound amount to -1.22 J/K⋅kg, -0.6 J/K⋅kg and -0.09 J/K⋅kg at 7, 5 and 2 T respectively. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Materials based on gadolinium are prospective for applications in magnetic refrigeration cycles. Recently, magnetic materials with relatively high Curie temperatures (T C ) are researched as potential candidates for magnetic refrigeration, providing that they show large enough magnetocaloric effect (MCE). Among them are several intermetallics based on rare earths and transition metals [1-4]. The structure of the equiatomic rare earth (R) compounds RCu changes with the atomic number of the rare earth constituent. RCu with light R constituents crystallize in the orthorhombic FeB-type structure, those with heavy R in the CsCl-type structure. The compounds with R = Gd, Tb and Y show a lattice instability. The crystal structure of GdCu transforms from the cubic CsCl-type to the orthorhombic FeB-type below 250 K [5], which has been identified as a martensitic transformation [6]. It is accompanied by large thermal hysteresis with pronounced anomalies in unit cell volume and electrical resistivity. However, the CsCl-type structure can be recovered after appropriate heat treatment up to 620 K [7]. The GdCu exhibits magnetic transition at T N = 150 K for CsCl-type and T N = 45 K for FeB-type [8]. Recently, X-ray absorption spectroscopy results showed the change of the electronic structure, which suggest that the s-d hybridization plays the major role for the crystal transformation [9]. The heat capacity and magnetocaloric effect of GdZn compound (CsCl-type) has been characterized by Pecharsky and Gschneidner [10]. It is ferromagnetic with a Curie temperature of 270 K. The magnetocaloric effect reaches values of −7 J/kg⋅K and −11 J/kg⋅K for magnetic field changes of 5 and 10 T, respectively. The magnetocaloric effect in GdZn is approximately 30% smaller than that observed in pure Gd [10]. Recently, other compounds with well known magnetic properties are examinted in terms of magnetocaloric effect. The GdCu have been investigated for several years and shows some features characteristic for the useful magetocaloric materials such as: presence of a lanthanide, 50% magnetic atoms or martensitic transformation [11]. Therefore, it is interesting to examine the MCE properties of GdCu in more detail. This paper describes the magnetic and magnetocaloric effect of GdCu intermetallic compound. 2 Experimental Single crystal of GdCu was grown by the Czochralski method from a small amount of the high purity starting materials. They were melted together in stoichiometric amounts on a water-cooled eight-segment 14 mm ____________________ * Corresponding author: e-mail: monika.oboz@us.edu.pl