Experimental determination of the magneto-optic constants of rare-earth transition-metal alloys

The complex magnetooptic constants of rare-earth-transition-metal alloys have been determined from accurate measurements of the polar Kerr rotation of a series of samples of differing thicknesses, deposited on quartz coupons with protective overcoats, by least-squares fitting to the multilayer optical equations of the structure. Films were deposited by DC magnetron sputtering from a Tb₂₀(Fe₉₀Co₁₀)₈₀ compound target. Rutherford backscattering analysis shows that the actual Tb content in the films is about 18.1%, and that the Ar content is less than 0.5%. The overcoats were Al₂O₃, with a measured refractive index of 1.63, RF-diode sputtered from a compound target in the same system. Kerr rotation was measured at room temperature at 820-nm wavelength. Measurements made with and without the overcoat are presented and discussed