Magnetic properties of RF diode sputtered CoxFe100-x alloy thin films

The systematic variations in the magnetic properties of as-deposited (by RF diode sputtering) and annealed Co_xFe_100-x (x=0, 15, 50, 67, 90, 100) alloy thin films were studied in this work. Maximum values of 4πM_s (21.3 kGauss) and H_c (253 Oe) were observed in as-deposited films with, respectively, x=15 and x=50. Films with 0⩽x⩽15 had rotatable hysteresis loops with squareness S≈1. With increasing Co, S decreased and the films became isotropic. Large decreases in H_c and resistivity, and large increases in 4πM_s were produced in films with x=50 and 67 by annealing in vacuum at 370°C, in the presence of an in-plane field. The in-plane anisotropy of the annealed films had a complex biaxial symmetry. A similar biaxial anisotropy was observed in Co₉₀Fe₁₀ films deposited in an ≈200 Oe planar field. This anisotropy was observed independent of whether the substrate was crystalline Si, glass or polyimide. Thus the biaxial anisotropy could not be ascribed to structural constraints at the film-substrate interface, but was probably induced in the film during deposition. The optimum binary CoFe alloy films for application at GHz frequencies require highly oriented uniaxial anisotropies. For reasons not fully understood, it was not possible to obtain well oriented as-deposited, or annealed, binary CoFe films with uniaxial anisotropy