RELATIONSHIP BETWEEN WEAK FERROMAGNETISM AND MAGNETIC IRREVERSIBILITIES IN GD2CUO4

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 di fferent temperatures both by solid-state reaction and by a sol-gel tec hnique allowing control of the final size of the sample particles. Cha nges in the magnetothermal dependence of dc magnetization and in the f requency dependence of the ac susceptibility, are observed for the cer amic samples. We regard the starting temperature of irreversibilities in dc magnetization as a blocking temperature for a system of WF domai ns or clusters. In the sol-gel particles a size reduction depresses th e blocking temperature, which is interpreted as the limitation of the WF domains extension by the particle size. The results are discussed i n a framework that accounts for coherent displacements of the oxygen i n the CuO2 planes as the origin of the WF domains.