Effects of Cu-doping on the magnetic state of Zn(0.9-x)Fe0.1Cu(x)O.

Magnetization measurements were performed on a series of Zn(0.9-x)Fe0.1Cu(x)O samples (0 < x approximately 0.1) prepared using solid state reaction and sol-gel methods. Although Cu is nonmagnetic, we found that increasing Cu content increases the saturation magnetization and enhances the hysteresis losses. Curie behavior of the susceptibility at high temperature indicates the presence of ferromagnetic exchange interaction. Moreover, we found that the exchange interaction and the molecular field coefficient are both ferromagnetic and greatly enhanced with Cu-doping; however, the Arrott-Belov-Kouvel plot did not reveal the presence of spontaneous magnetization down to 4.2 K.