Origin of anomalously high exchange field in antiferromagnetically coupled magnetic structures: Spin reorientation versus interface anisotropy

Abstract

A physical model of exchange bias in [ Pd / Co ] 5 / FeMn thin films with perpendicular anisotropyCorrelation between perpendicular exchange bias and magnetic anisotropy in IrMn ∕ [ Co ∕ Pt ] n and [ Pt ∕ Co ] n ∕ IrMn multilayers Magnetization reorientation from in-plane to perpendicular direction, observed in Co thin film coupled antiferromagnetically to high perpendicular magnetic anisotropy (Co/Pd) multilayers, is studied systematically for Co thickness ranging from 0 to 2.4 nm. The sample with 0.75 nm thick Co showed an exchange coupling field (H ex ) exceeding 15 kOe at room temperature and 17.2 kOe at 5 K. With an increase of Co thickness, H ex decreased as expected and beyond certain thickness, magnetization reorientation was not observed. Indeed, three regions were observed in the thickness dependence of magnetization of the thin layer; one in which the thin layer (in the thickness range up to 0.8 nm) had a perpendicular magnetic anisotropy due to interface effects and antiferromagnetic coupling, another in which the thin layer (0.9-1.2 nm) magnetization had no interface or crystallographic anisotropy but was reoriented in the perpendicular direction due to antiferromagnetic coupling, and the third (above 1.2 nm) in which the magnetization was in-plane. In addition, Hall effect measurements were carried out to observe the anomalous and planar Hall voltages and to quantify the perpendicular and in-plane components of magnetization. The sample with thicker Co layer (2.4 nm) showed an in-plane component of magnetization, whereas the sample with 0.75 nm Co showed no in-plane component. The high value of H ex observed in 0.75 nm Co samples can have important implications in spintronics and bit patterned media.

Magnetic properties of antidots in conventional and spin-reoriented antiferromagnetically coupled layers

“…In this context, our recent observation of spin reorientation arising from antiferromagnetic coupling between two magnetic layers could be helpful. 13,14 We have reported H ex in excess of 7 kOe when thin Co layers (about 0.8 nm) are antiferromagnetically coupled to a recording layer.…”