IMPROVEMENT OF THE MAGNETIC-PROPERTIES OF CONICR THIN-FILMS BY ANNEALING

The changes in the magnetic properties of CoNiCr/Cr thin films with annealing are found to depend not only on the annealing conditions but also on the Cr underlayer thickness dCr. After vacuum anneal, the in-plane coercivity Hc increased initially with total annealing time τa and then leveled off. The Hc increase was greater at higher annealing temperatures Ta and in samples with thicker Cr underlayers. Hc values as high as 1800 Oe were obtained. The squareness S* decreased with τa, and the saturation magnetization Ms decreased slightly with τa. No significant change was found in the grain size and the crystal texture of the films after annealing, regardless of the Cr underlayer thickness. However, for the sample with a large Hc increase following anneal, it was found that the corresponding Lorentz micrograph image changed dramatically. TEM x-ray energy dispersive data indicated that the Cr concentration in the CoNiCr layer increased after anneal. The changes in Hc, S*, and M s following air anneal were similar to those found following vacuum anneal. However, at the same Ta, the increase in Hc was less; also Ms was found to decrease noticeably. We believe that the changes in magnetic properties following anneal are associated with increased Cr content in the grain boundaries.