Magnetic properties of RF diode sputtered Co/sub x/Fe/sub 100-x/ alloy thin films

The systematic variations in the magnetic properties of as-deposited (by RF diode sputtering) and annealed Co/sub x/Fe/sub 100-x/ (x=0, 15, 50, 67, 90, 100) alloy thin films were studied in this work. Maximum values of 4/spl pi/M/sub s/ (21.3 kGauss) and H/sub c/ (253 Oe) were observed in as-deposited films with, respectively, x=15 and x=50. Films with 0/spl les/x/spl les/15 had rotatable hysteresis loops with squareness S/spl ap/1. With increasing Co, S decreased and the films became isotropic. Large decreases in H/sub c/ and resistivity, and large increases in 4/spl pi/M/sub s/ were produced in films with x=50 and 67 by annealing in vacuum at 370/spl deg/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 Co/sub 90/Fe/sub 10/ films deposited in an /spl ap/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.