Magnetic and Structural Properties of Fully Epitaxial ${\hbox {Fe}}_{3}{\hbox {O}}_{4}/{\hbox {MgO/GaAs}}(100)$ for Spin Injection

In this paper, the authors report on the investigation on the effect of inserting an epitaxial MgO layer on the structural and magnetic properties of ${\hbox {Fe}}_{3}{\hbox {O}}_{4}$ ultrathin films grown on GaAs(100) by combined techniques of molecular beam epitaxy and postgrowth annealing in an oxygen atmosphere. The MgO films were grown with a cube-on-cube orientation to GaAs. The epitaxial ${\hbox {Fe}}_{3}{\hbox {O}}_{4}$ lattice cell was rotated by 45$^{\circ}$ in respect to that of MgO and GaAs due to the lattice relaxation of the magnetic layer. All samples studied exhibited strong fourfold cubic magnetic anisotropy with easy axes along the $\langle 001\rangle$ directions of GaAs. A dramatic decrease in the uniaxial anisotropy constant in the presence of the MgO barrier was observed. The existence of the uniaxial magnetic anisotropy in the ${\hbox {Fe}}_{3}{\hbox {O}}_{4}/{\hbox {GaAs}}$ hybrid structure has been attributed to the interfacial contact between the magnetite film and the GaAs.