Magnetostriction and magnetocrystalline anisotropy constants of ultrathin epitaxial Fe films on GaAs, with Au overlayers

摘要

In this paper, we present the first measurements on the variation of the saturation magnetostriction constant with film thickness of ultrathin epitaxial Fe films on GaAs(100) substrates. Furthermore, we explore whether there is a link between magnetostriction and the uniaxial anisotropy in these Fe films. The Fe film thickness ranged from seven monolayers (ML) (having only uniaxial anisotropy) to 50 ML (almost pure cubic anisotropy). The anisotropy constants were determined from the normalized magnetization loops, using a magneto-optic Kerr effect (MOKE) fitting technique that convolutes a magnetic energy density model with the dependence of the MOKE signal on the angle between the pass plane of the analyser and the plane of incidence of the laser light on the sample. Each film was uniformly strained along the [011] direction, while the magnetization was measured along the [011] direction using a MOKE magnetometer. From the change in anisotropy field as a function of strain (Villari effect), the magneto stricti on constant in the [011] direction was calculated. It is demonstrated that the saturation magnetostriction constant in the [011] direction is significantly different to the equivalent value in bulk Fe, and increases in magnitude as the thickness of the Fe film decreases. It will also be shown that the uniaxial anisotropy constant has a linear dependence on the magnetostriction constant for each film.