Enhancement of the exchange-bias onset temperature in a columnar nanocrystalline Ni_(80)Fe_(20)/Co_3O_4 thin film

摘要

Typically, exchange coupling can only occur when ferromagnetic spins couple to antiferromagnetic spins below the Neel temperature. We present results on a Ni_(80)Fe_(20)/Co_3O_4 thin film that is composed of approx 10 nm diameter nanocrystailine columns. Field cooling the film reveals low-temperature exchange-bias hysteresis loop shifts that are the same magnitude as those measured in a similar Ni_(80)Fe_(20)/CoO system, although the bulk magnetocrystalline anisotropy is a factor of 5 smaller. The coercivity and exchange-bias loop shift exhibit the same temperature dependence with individual "blocking" temperatures. Most surprising is that the onset temperature of the exchange-bias is nearly four times higher than the bulk Neel temperature.