INPLANE MAGNETIZATION ANISOTROPY IN GD2CUO4 SINGLE-CRYSTALS

We present here detailed de magnetization measurements of a Gd2CuO4 single crystal. Besides the strong out-of-plane anisotropy that favors the orientation of the magnetization within the CuO2 planes for R(2) CuO4, we have also found in-plane anisotropy when the external field H is applied parallel to the CuO2 planes. Three regions could be distinguished in magnetization M vs field curves: for O < H < H-c' approximate to 35 G, M is only slightly anisotropic. A metamagneticlike transition is observed when H is parallel to an anisotropy easy axis, coincident with one [110] direction. Above this transition a ''hidden'' weak ferromagnetic component develops. For H-c' < H < H-c* approximate to 300 G strong anisotropy is found, and above the critical field H-c* all magnetic moments are completely aligned with the external field and the magnetization is again isotropic. Hysteretic behavior has been observed at the metamagnetic transition, probably due to the existence of weak ferromagnetic domains. An intraplanar anisotropy field H-x approximate to 1200 G and an interplanar coupling constant J(perpendicular to) approximate to 2 mK, have been estimated from the experimental critical fields using a mean field description of the magnetic coupling between CuO2 planes.