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 CoxFe100-x (x=0, 15, 50, 67, 90, 100) alloy thin films mere studied in this work. Maximum values of 4 pi M(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 less than or equal to x less than or equal to 15 had rotatable hysteresis loops with squareness S approximate to 1. With increasing Co, S decreased and the films became isotropic. Large decreases in H-c and resistivity, and large increases in 4 pi M(s) were produced in films with x=50 and 67 by annealing in vacuum at 370 degrees 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 deposed in an approximate to 200 Oe planar field. This anisotropy was observed independent of whether the substrate ws 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 depositon. 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.