Magneto-optical Kerr effect in Fe21Ni79 films on Si(100): Quantum behavior for film thicknesses below ∼6 nm

Abstract

The magneto-optical Kerr effect (MOKE) has been observed and characterized in 1–80 nm thick Fe21Ni79 films deposited onto Si(100), for an external magnetic field (variable in strength up to 400 G) oriented parallel or orthogonal to the magnetization axis of the film. A measurable response is observed for film thicknesses (d) as small as 2 nm and, if the external magnetic field lies in the plane of the film, two-dimensional quantum behavior is evident for d≲6 nm. A precipitous decline in the magnitude of the MOKE response is accompanied by an increase in the coercivity and, when the external field is perpendicular to the film magnetization axis, a rapid rise in the saturation field. Experiments also confirm the existence of a component of the film magnetization oriented out of the plane of the film, a result consistent with the prediction of computational studies [T. Trunk et al., J. Appl. Phys. 89, 7606 (2001)] that the transition between Bloch and Néel wall domain structure occurs in FeNi films for film thicknesses of ≈30 nm.