Inverted hysteresis in exchange biased Cr2O3 coated CrO2 particles

Abstract

Exchange bias and inverted hysteresis loops were observed in the Cr2O3 coated CrO2 particles with a wide distribution of the blocking temperature. The ferromagnetic coupling between the CrO2 cores and Cr2O3 shell is responsible for exchange bias observed below 292K. In the temperature range of 261K–∼340K, the particles show inverted hysteresis loops, i.e., the negative remanence and coercivity. The most interesting observation is that the particles show an exchange-biased (or shifted) inverted hysteresis loops in between 261K and 292K; and that the maximum negative remanence appears at 292K where exchange bias disappears. An antiferromagnetic type of interaction between the blocked particles and the superparamagnetic particles is believed to be responsible to the inverted hysteresis loops.