Perpendicular exchange bias and magnetic anisotropy in CoO/permalloy multilayers

Abstract

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