Magnetic Properties and Structure of CoCr Thin Films

CoCr films with thicknesses ranging from 0.014 ¿m to 0.5 ¿m were prepared by dc magnetron sputtering onto PET film, using a CoCr alloy (18 wt% Cr) target. Thicker films are characterized by three zones with different magnetic properties. In the first zone, for thicknesses up to 0.03 ¿m, films have very low coercive forces Hc and small saturation magnetizations Ms, as well as a poor perpendicular anisotropy. In the second zone, for thicknesses from about 0.03 ¿m to 0.1 ¿m, the Hc and Ms vary, both passing through maxima, but the anisotropy field is smaller than that prevailing in the third zone. In this third zone, Hc gradually decreases with increasing film thickness, while Ms approaches a constant value and Hk reaches its highest constant value. TEM studies showed CoCr films to have a fine columnar structure, with column thicknesses greater than 0.03 ¿m, and no changes in structure or column diameter were observed for films in the second and third zones. To investigate the effects of the underlayer, various kinds of metal were deposited on the PET film prior to CoCr deposition. Double-layer CoCr films exhibit higher Hc values than single-layer films, and have poor crystalline orientations. SEM observations indicate that CoCr films with a metallic underlayer have smaller grain sizes than do single-layer films.