Interfacial coupling effect of Cr₂O₃ on the magnetic properties of Fe₇₂Ga₂₈ thin films

Here it is investigated the effect of the antiferromagnet Cr₂O₃ on the magnetic properties of ferromagnetic Fe₇₂Ga₂₈ thin films. Sputtered Fe₇₂Ga₂₈ 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 Cr₂O₃ that has magnetic moments along the c-axis, that is the perpendicular direction when properly aligned. Cr₂O₃ has been obtained from Cr oxidation, whereas Fe₇₂Ga₂₈ has been deposited on top of it by sputtering in the ballistic regime. Although a uniaxial in-plane magnetic anisotropy is expected for Fe₇₂Ga₂₈ thickness above 100 nm, the interfacial coupling with Cr₂O₃ prevents this anisotropy. The formation of stripe domains in Fe₇₂Ga₂₈ above a critical thickness reveals the enhancement of the out of plane component of the Fe₇₂Ga₂₈ 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 3·10⁶ erg·cm^-3 is inferred from experimental results. Eventually, the coupling between Cr₂O₃ and Fe₇₂Ga₂₈ promotes an exchange-bias effect that has been well fitted by means of the random field model.