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, Ku eff 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 Ku eff from the as-grown value of 8.9× 103 to 1.1× 105 J/ m3. The slope of Ku eff 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 Ku eff 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. © 2008 American Institute of Physics.