Nanostructure and magnetic properties of the MnZnO system, a room temperaturemagnetic semiconductor?

Abstract

The magnetic properties of the system MnZnO prepared by conventional ceramic procedures using ZnOand MnO2 starting powders are studied and related to the nanostructure. Thermal treatment at500 °C produces a ferromagnetic phase, although this temperature is not high enough to promoteproper sintering; thus the thermally treated compact shows brittle characteristics of unreactedand poorly densified ceramic samples. Scanning electron microscopy and x-ray analysisreveal the appearance of a new phase, most probably related to the diffusion of Zn intoMnO2 oxide nanocrystals. The magnetic properties deviate considerably from whatwould be expected of an unreacted mixture of ZnO (diamagnetic) andMnO2 particles (paramagnetic above 100 K and anti-ferromagnetic below that temperature), exhibiting aferromagnetic like behaviour from 5 to 300 K and beyond mixed with a paramagnetic component.The ferromagnetic phase seems to be originated by diffusion at the nanoscale of Zn intoMnO2 grains. The Curie temperature of the ferromagnetic phase, once the paramagneticcomponent has been subtracted from the hysteresis loops, is measured to be 450 K. EPRresonance experiments from 100 to 600 K confirm a ferromagnetic to paramagnetic liketransition above room temperature for these materials.