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/t_FM and 1/t_FM^3/2 (t_FM= permalloy layer thickness), respectively. At the same time, the remanent ratio increases with decreasing t_FM. The induced effective uniaxial anisotropy changes as a linear function of 1/t_FM, as a symbol of an interface anisotropy. The interface anisotropic energy increases with decreasing temperatures. For samples with small t_FM, 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.