Room temperature ferromagnetic phase in ZnO-MnO2 system via solid-state reaction

Only mechanical milling of a mixture of powders composed of MnO2 and ZnO brings about a phase which exhibits ferromagnetic behavior at room temperature. The sample just after the mechanical milling without any heat treatments at elevated temperatures clearly manifests a hysteresis loop in magnetic field dependence of magnetization at 300 K; the residual magnetization is 2.84 x 10(-4) emu/g and the coercive force is 76Oe. It should be emphasized that the residual magnetization rather decreases when the as-milled sample is heat treated. The ferromagnetic behavior is thought to be attributed to Zn-doped manganese oxide phase formed on the surface region of MnO2 particles. (c) 2006 Elsevier B.V. All rights reserved.