Magnetocrystalline anisotropies and magnetostriction of ultrathin Fe films on GaAs with Cr overlayers

Abstract

In this article we present data which show that Cr overlayers on epitaxial Fe films on GaAs substrates change the magnetic properties of the films in comparison to Au overlayers. For films thinner than 50 ML, the presence of the Cr overlayer reduced the magnitude of the uniaxial anisotropy in the Fe film, while for a 150 ML film, there was still a strong uniaxial anisotropy present. The anisotropy constants were determined using a modified energy density model, and were found to be smaller than those for Au overlayer films. The absolute magnetizations were measured on a vibrating sample magnetometer. It was determined that for the same thickness of Fe the magnetization with a Cr overlayer was 75% of that for a Au overlayer. This was either due to the Cr alloying with the Fe at the interface, or the Cr forming CrO2 on the surface of the film. The magnetostriction constant was determined using the Villari effect. For all the films the saturation magnetostriction constant was more negative than the bulk Fe value.