Perpendicular exchange bias and magnetic anisotropy in CoO/permalloy multilayers

For permalloy/CoO multilayers, after perpendicular field cooling, perpendicular exchange bias has been observed below room temperature. For out-of-plane hysteresis loops, the exchange field and the coercivity at fixed temperatures are proportional to 1/tFM and 1/tFM3/2 (tFM=permalloy layer thickness), respectively. At the same time, the remanent ratio increases with decreasing tFM. The induced effective uniaxial anisotropy changes as a linear function of 1/tFM, as a symbol of an interface anisotropy. The interface anisotropic energy increases with decreasing temperatures. For samples with small tFM, perpendicular anisotropy films can be established at low temperature. The established perpendicular magnetic anisotropy and its remarkable temperature dependence might facilitate perpendicular magnetic recording and magneto-optical storage techniques.