Interfacial coupling effect of Cr_2O_3 on the magnetic properties of Fe_72Ga_28 thin films

Abstract

Here it is investigated the effect of the antiferromagnet Cr_2O_3 on the magnetic properties of ferromagnetic Fe_72Ga_28 thin films. Sputtered Fe_72Ga_28 layers have their magnetization in the sample plane with a magnetic fluctuation that gives rise to magnetic ripple. In order to turn its magnetization into the out of plane (OOP) direction, it has been magnetically coupled with Cr_2O_3 that has magnetic moments along the c-axis, that is the perpendicular direction when properly aligned. Cr2O3 has been obtained from Cr oxidation, whereas Fe_72Ga_28 has been deposited on top of it by sputtering in the ballistic regime. Although a uniaxial in-plane magnetic anisotropy is expected for Fe_72Ga_28 thickness above 100 nm, the interfacial coupling with Cr2O3 prevents this anisotropy. The formation of stripe domains in Fe_72Ga_28 above a critical thickness reveals the enhancement of the out of plane component of the Fe_72Ga_28 magnetization with respect to uncoupled layers. Due to the interface coupling, the Fe72Ga28 magnetization turns into the out-of-plane direction as its thickness is gradually reduced, and a perpendicular magnetic anisotropy of 3.10^6 erg.cm^(-3) is inferred from experimental results. Eventually, the coupling between Cr_2O_3 and Fe_72Ga_28 promotes an exchange-bias effect that has been well fitted by means of the random field model.