Solid-state reactions in Ga/Mn thin films: Formation and magnetic properties of the ϕ-Ga7.7Mn2.3 phase

Experimental results concerning the solid-state synthesis of the ϕ-Ga_7.7Mn_2.3 phase in Ga/Mn thin films are presented. A ferromagnetic (or ferrimagnetic) state is observed in the samples annealed at temperatures above 250°C. The X-ray diffraction studies demonstrate the formation of the ϕ-Ga_7.7Mn_2.3 phase, which is poly-crystalline being grown on glass substrates and exhibits the preferential cube-on-cube orientation on MgO(001) substrates. A strong dependence of the perpendicular anisotropy constant K _⊥ and of the effective biaxial anisotropy constant K ₁^eff on the magnetic field H has been found. Owing to such dependence, the easy axis of magnetization lying in the plane of the film changes its direction approaching the film normal when the increasing magnetic field exceeds 8 kOe. The anomalous behavior of K _⊥ and K ₁^eff constants is explained both by the in-plane stresses arising in the course of the formation of the ϕ-Ga_7.7Mn_2.3 phase and by the direct dependence of magnetostriction constants on the magnetic field. For the ϕ-Ga_7.7Mn_2.3 phase, the saturation magnetization M _S has been determined and the first magnetocrystalline anisotropy constant K ₁ has been estimated.