The magnetic properties of Gd2Co17−xGax compounds

Abstract

X-ray diffraction (XRD) and magnetization measurements were performed to investigate the effect of Ga substitution for Co on the structural and magnetic properties of Gd2Co17−xGax compounds (x=0, 1, 2, 3, 4, 5, 6, 7, and 8). Crystal-structure studies indicate that all samples are single phase with the rhombohedral Th2Zn17-type structure except for the samples with x=7 and 8, which contain a small amount of Co. The Ga substitution for Co in Gd2Co17 compounds leads to a monotonic increase in the unit cell volume and an approximately linear decrease in the saturation magnetization. The Curie temperature TC is found to decrease monotonically from 1210 K for x=0 to 30 K for x=8. The compensation points are observed for the Gd2Co17−xGax samples with x=5 and 6. The value of the compensation temperature, determined from the temperature dependence of the magnetization measured in a magnetic field of 1000 Oe, is 120 and 152 K for x=5 and 6, respectively. It is noteworthy that the substitution of Ga for Co in the Gd2Co17 compounds has a remarkable influence on the magnetocrystalline anisotropy. XRD studies on magnetic-field oriented Gd2Co17−xGax powders show that the sample with x=0 exhibits an easy-plane anisotropy, while the samples with x⩾1 exhibit an easy c-axis anisotropy at room temperature. The change of the easy magnetization direction of Gd2Co17−xGax compounds from a basal plane to c axis indicates that the substitution of Ga for Co leads to the decrease of the planar anisotropy of the Co sublattice.