Closely linear temperature dependence of exchange bias and coercivity in out-of-plane exchange-biased [Pt/Co]3/NiO (11 Å) multilayer

Strong out-of-plane exchange biasing has been observed in out-of-plane exchange biased [Pt (5 Å)/Co (4 Å)]3/NiO (11 Å) multilayer with perpendicular easy axis. Both the exchange field HE and coercivity HC display a closely linear temperature dependence except at very low temperatures. A thin NiO layer coated on the top of a Pt/Co multilayer has a great effect on the domain pattern of the Pt/Co multilayer, which is in a more irregular configuration with much smaller domain sizes than the uncoupled Pt/Co multilayer. A simulation according to Malozemoff’s random field model gives a good agreement to the experimental temperature dependence of HE and HC, suggesting that the closely linear temperature dependences of HE and HC are strongly related to the behavior of the temperature of anisotropies and of the spin rotation inside the domain walls of a thin NiO layer. The blocking temperature of TB=220 K is much higher than that observed in ferromagnetic/thin NiO systems with in-plane anisotropy.