Room temperature ferromagnetic behavior in Cr₂O₃ nanoparticles prepared by a planetary ball mill system

Abstract

Recently, room temperature ferromagnetism (RTFM) has been reported to be found in many kinds of oxide semiconductor nanoparticles. The origin of the magnetic moment is believed to defects because RTFM strongly depends on the particle size. In this study, we have focused on antiferromagnetic insulator Cr2O3 due to the interesting core-sell structure (RTFM/antiferromagnetism). Furthermore, RTFM found in oxide nanoparticles is expected to depend on the sample preparation condition. Here, the effect of sample preparation condition on RTFM was investigate. Samples were nanoparticles prepared by milling oxide powders in Ar or air circumstance. Both samples indicated hysteresis at room temperature. At higher temperature than Néel temperature (308 K), hysteresis loops were found. Significant difference was observed in the saturation magnetization. The sample prepared in air has four times smaller saturation magnetization in 60 min milling time due to self-compensation of defects with air.