Structure and magnetic properties of amorphous Co-Si alloy films

Co_xSi_1-x alloy films have been prepared by sputtering in the composition range 0.65 ≤ x ≤ 1 at room temperature, and their structural and magnetic properties have been characterized by X-ray diffraction, extended X-ray absorption fine structure spectroscopy, and by magnetooptical Kerr effect magnetometry. The samples are polycrystalline with a mixture of fcc and hcp phases down to x = 0.76. For lower Co content, there is a transition to an amorphous structure that can be described by a dense random packing of hard spheres model. For x = 0.65 a change is found in the atomic environment of the Co atoms in the amorphous structure, that becomes more similar to a disordered Co₂Si phase. These structural changes are reflected also on the magnetic properties of the films: essentially isotropic with high coercivity for x ≥ 0.76, with well-defined uniaxial magnetic anisotropy in the 0.75 ≥ x ≥ 0.66 composition range, and non magnetic for x below 0.65.