Weak ferromagnetism in Gd 2CuO 4 and Gd 2−xR xCuO 4±δ(R = Ce, Sr).

Abstract

Gd 2CuO 4 developes, at T N, a long range AF order with a weak ferromagnetic (WF) component. This component is allowed by in-plane distortions of the tetragonal T' structure and persists above T N, induced by the magnetic field, in a large temperature interval. From dc magnetization measurements, we have accurately determined the WF transition, which follows the characteristic law of classical ferromagnets, h = t( γ+ β), with ( γ+ β) = 1.8(2). The WF component persists in Gd 1.85Ce 0.15CuO +δ, even after a reduction procedure, although the Ce 4+ doping lowers T N. A set of Gd 2−xSr xCuO 4−δ samples, prepared via a sol-gel method at a maximum temperature of 900°C, showed an expanded unit cell without distortions, the absence of a WF component and strongly modified magnetic properties of the Gd sublattice.