Electrical resistivity and magnetic investigations of the orthorhombic Tb(Ni,Cu)2 system

The orthorhombic Tb(Ni, Cu)₂ and Gd(Ni, Cu)₂ systems (CeCu₂ structure) are closely similar according to electrical resistivity and magnetic results. The Tb(Ni_xCu_1?x)₂ system presents a transition from antiferromagnetism (AF) for x ? 8% Ni to ferromagnetism (FM) for x > 8% Ni. The CeCu₂ structure becomes unstable for x > 45% Ni. The AF samples show metamagnetism at 4.2 K with critical fields. Hysteresis, which occurs for all samples at 4.2 K, is attributed to intrinsic pinning due to large anisotropy where the mechanism for the AF range is analogous to intrinsic pinning of narrow domain walls in FM samples.Spin disorder resistivity measurements show a discontinuity at the AF-FM transition composition for both the Tb and Gd systems. This is due to a step up of the residual resistivity at 4.2 K as a result of AF ordering. This interpretation is confirmed by applying a magnetic field to destroy the AF ordering.