Enhanced uniaxial magnetic anisotropy in Fe31Co69 thin films on GaAs(001)

Abstract

We report on the effect of postgrowth annealing on the magnetic anisotropy of Fe31Co69 thin epitaxial films, 1–9 nm thick, and grown on GaAs(001) substrates. Hysteresis curves obtained by means of the magneto-optical Kerr effect reveal an in-plane uniaxial magnetic anisotropy with the easy axis typically along the [110] substrate direction. The effective in-plane and perpendicular anisotropy constants, Kueff and K⊥eff, exhibit a steep quasilinear increase with the annealing temperature. Annealing a 1.9-nm-thick film for 10 min at 300 °C results in an increase in Kueff from the as-grown value of 8.9×103 to 1.1×105 J/m3. The slope of Kueff versus annealing temperature increases approximately as the inverse of the film thickness. These observations can be accounted for by a thermally induced structural modification occurring in the ferromagnet-semiconductor interface. Film-strain measurements performed by x-ray grazing-incidence diffraction indicate that the postgrowth annealing evolution of Kueff and K⊥eff are not predominantly induced by a magnetoelastic effect associated with strain changes in the thin film, but rather by modifications of the interface atom bonding, leading to an enhanced magnetocrystalline anisotropy at the ferromagnet-semiconductor interface.