Comparison between magneto-optic and VSM measurements of bias-sputtered CoCr films with perpendicular anisotropy

A direct comparison between surface and bulk hysteresis behavior is made on a variety of bias-sputtered CoCr films using magnetooptic and VSM (vibrating sample magnetometer) techniques. The results show that bias sputtering at around -100 V leads to an improvement in the surface as well as the volume magnetic properties of CoCr films. Furthermore, a reversal in the magnitude of surface and volume coercivities is observed when the Cr content of the films exceeds 13 at.% and the film thickness increases above 0.4 μm. These effects are attributed to the presence of pores on the film surface which affect the demagnetizing factor of the surface with respect to the volume. The magnetooptical rotation signal obtained from the surface and the back of the films is used to assess their respective saturation magnetization and, hence, the extent of Cr solubility or segregation at the two boundaries