Magnetism and hyperfine interactions in Gd2Ni2Mg

Gd2Ni2Mg was synthesised by reaction of the elements in a sealed tantalum t ube in a high-frequency furnace. The structure was investigated by single c rystal X-ray diffraction: Mo2FeB2 type, P4/mbm, a = 743.8(1), c = 375.3(1) pm, wR(2) = 0.0560, 256F(2) values, 12 variables. The Gd2Ni2Mg structure is an intergrowth of distorted AlB2 and CsCl slabs of compositions GdNi2 and GdMg. The magnetic phase transitions were studied by AC and DC magnetic sus ceptibility measurements and Gd-155 Mossbauer spectroscopy. Antiferromagnet ic ordering is detected at T-N = 49.00(5) K followed by two further transit ions at T-f1 = 20.70(5) and T-f2 = 4.5(1) K, respectively. Non-vanishing se cond and third harmonic components of the induced voltage under application of a small AC magnetic field reveal the ferromagnetic nature of the second transition at T-f1. Below T-f1, Gd2Ni2Mg shows strong irreversibility betw een field cooled (FC) and zero field cooled (ZFC) DC magnetization and magn etic hysteresis behaviour. (C) 2001 Editions scientifiques et medicales Els evier SAS. All rights reserved.