Relationship between weak ferromagnetism and magnetic irreversibilities in Gd2CuO4.

Abstract

Detailed dc and ac magnetic susceptibility measurements have been made on a series of polycrystalline Gd2CuO4. This system crystallizes in a distorted T phase with a reduced orthorhombic symmetry and exhibits a weak ferromagnetic (WF) behavior. The samples were synthesized at different temperatures both by solid-state reaction and by a sol-gel technique allowing control of the final size of the sample particles. Changes in the magnetothermal dependence of dc magnetization and in the frequency dependence of the ac susceptibility, are observed for the ceramic samples. We regard the starting temperature of irreversibilities in dc magnetization as a blocking temperature for a system of WF domains or clusters. In the sol-gel particles a size reduction depresses the blocking temperature, which is interpreted as the limitation of the WF domains extension by the particle size. The results are discussed in a framework that accounts for coherent displacements of the oxygen in the CuO2 planes as the origin of the WF domains. © 1995 The American Physical Society.