Evidence for room temperature ferromagnetism in Cux Zn1-x O from magnetic studies in Cux Zn1-x OCuO composite

Magnetic studies in bulk 57% Cux Zn1-x O43% CuO composite prepared chemically with x=0.10 (0.03) are reported. Temperature dependence of the magnetic susceptibility shows clear signature of the Ńel temperature TN ≃230 K for pure CuO. Hysteresis loop studies in the zero-field-cooled sample show room-temperature ferromagnetism with coercivity Hc ≃50 Oe at 300 K with strong temperature dependence for T<300 K. A negative exchange bias He at 5 K is observed when the sample is cooled from RT in H=20 kOe, and its temperature dependence yields He →0 at TN =230 K of CuO. These results and the temperature dependence of remanence Mr provide strong evidence that the Cux Zn1-x O phase with x≃0.10 is a ferromagnet with Tc ≃400 K. An electron magnetic resonance signal due to Cu2+ substituting for Zn2+ in Cux Zn1-x O is also observed.