Journal of Alloys and Compounds 509 (2011) 4478–4483 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Physical properties of Gd 7 NiPd 2 single crystal M. Oboz ∗ , E. Talik, J. Kusz, A. Winiarski Institute of Physics, University of Silesia, Uniwersytecka 4, 40 007 Katowice, Poland article info Article history: Received 18 November 2010 Received in revised form 3 January 2011 Accepted 4 January 2011 Available online 22 January 2011 Keywords: Rare-earth alloys and compounds Crystal growth Anisotropy Magnetocaloric abstract Investigations of X-ray diffraction, electronic structure, dc-magnetization M(T), ac-magnetic suscepti- bility  ac (T) and magnetocaloric properties for the Gd 7 NiPd 2 single crystal were performed. A single crystal of Gd 7 NiPd 2 was grown by the Czochralski method from a levitating melt. Anomalies in  ac (T) and M(T)-curves establish that Gd 7 NiPd 2 undergoes a long-range ferromagnetic-type ordering at T C = 298 K, followed by a spin-reorientation below 135 K. The magnetization data indicate that there is an excess magnetic moment calculated per Gd 3+ ions. The measured XPS valence band indicates the hybridiza- tion effect between Gd 5d, Ni 3d and Pd 4d states. The calculated values of entropy change Sm for the examined compound amount to -6.85 J/K kg for the a-axis and -6.49 for the c-axis at 7 T. © 2011 Elsevier B.V. All rights reserved. 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 if they show large enough magnetocaloric effect (MCE). Several intermetallics based on rare earth and transition metals show interesting magnetocaloric prop- erties [1–4]. However, their ordering temperatures are very often below room temperature. Preliminary examination of the crystal structure, magnetic and electrical behaviour of Gd 7-x Y x Pd 3 (x = 0, 1, 2, 3, 4, 5, 6) single crystals were performed [5–9]. Single crystals of solid solutions Gd 7-x Y x Pd 3 were reported to crystallize in the same structure as the parent Gd 7 Pd 3 compound [5–9]. In spite of yttrium substitution crystal structure was stable. With increasing Y-content the ferromagnetic transition shifts down to lower temperatures, whereas Gd 7 Pd 3 orders ferromagnetically below 334 K; Gd 6 YPd 3 , Gd 5 Y 2 Pd 3 and Gd 3 Y 4 Pd 3 undergo magnetic transformation at 299, 263 and 197 K, respectively. As a part of current research concerning the development of new magnets for magnetic refrigeration devices we characterised the Gd 7 NiPd 2 single crystal. This paper presents results of the crystal and electronic structure, magnetic and magnetocaloric properties investigations of a new Gd 7 NiPd 2 compound. 2. Experimental The single crystal of Gd7NiPd2 was grown by the Czochralski method from a levitated melt using high purity starting materials [10]. ∗ Corresponding author. Tel.: +48 32 359 1581; fax: +48 32 258 8431. E-mail address: monika.oboz@us.edu.pl (M. Oboz). The real structure of the as-grown crystal was examined by the Berg–Barrett topography using Fe K˛ radiation. The sensitivity of the method to the misorientation is ∼1 ′ . X-ray reflections from (h k l) planes were recorded in the range of 2 in the range 70–100 ◦ on Agfa-Gevaert Structurix D2 film, which was placed close to the crystal surface. The distance between the crystal and the film was about 1 mm to obtain a good pattern. These examinations were performed to check the quality of the obtained single crystals. The spatial resolution was 10 m. Single crystal X-ray diffraction was performed at room temperature on a four- circle KM4 diffractometer using graphite-monochromatized Mo K radiation. The intensities of reflections were corrected for Lorentz and polarization effects. XPS spectra of the above single crystal were measured with monochromatized Al K radiation (1486.6 eV) at room temperature using a PHI 5700 ESCA spectrometer. The energy spectra were determined by a hemispherical mirror analyzer with an energy resolution of about 0.3 eV. Magnetization was measured using a Quantum Design MPMSXL-7AC SQUID magnetometer in the temperature range 2–400 K in magnetic fields up to 7 T. The ac-magnetic susceptibility was measured in the temperature range 2–400 K and at a frequency of 100 Hz. 3. Results and discussion Fig. 1a shows a photo of “as-grown” Gd 7 NiPd 2 single crystal. Fig. 1b presents a topographic Berg–Barrett X-ray image of the stud- ied Gd 7 NiPd 2 single crystal. This image indicates that the obtained single crystal was good quality without mosaic structure. The crystal structure of the Gd 7 NiPd 2 was refined by the full least squares method using the SHELX-97 [11]. The results of the struc- tural refinements are collected in Table 1. The atomic coordinates, isotropic and anisotropic parameters are listed in Table 2. Apart from ascertaining the good single-crystalline quality of the sample, the X-ray diffraction data have showed that the Gd 7 NiPd 2 com- pound crystallized in the hexagonal Th 7 Fe 3 -type structure with space group P6 3 mc. From the tables one can recognize that in the unit cell of Gd 7 NiPd 2 the gadolinium atoms occupy three non- equivalent crystallographic positions (2b and 6c sites) and the 0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.01.034