Effect of lattice strain on soft magnetic properties in FeCo/NiFe(Cr) thin films with 2.4 T

The soft magnetic property of FeCo films with thin NiFe or NiFeCr seed layers (saturation flux density of 2.4 T) is discussed in relation to lattice strain of the FeCo films. The coercivity along hard axis of magnetization (H_c^HA) reduces as the Ar pressure during sputtering deposition decreases, and moreover, shows the lowest value at FeCo thickness of 50-100 nm. FeCo films show bcc-(110) preferred grain orientation with the <110> direction sharply perpendicular to the film plane. X-ray diffraction (XRD) patterns indicate that the absolute magnitude of the lattice strains of [110], (-110), and [001] planes reduce as the Ar pressure decreases. Magnetic anisotropy energy in [110] plane (E) was calculated by including magnetostrictive energy due to the lattice strain. It was successfully shown that the Ar pressure dependence of E is in good agreement with that of H_c^HA. Moreover, it is suggested that thickness dependence of H_c^HA is significantly related to that of magnetostrictive energy. It is likely that less lattice deformation, which is formed by the hetero-epitaxial growth of the FeCo[110] plane on the fcc-[111] plane of the NiFe(Cr) layer, is a key to derive soft magnetic properties in the FeCo/NiFe(Cr) films.