SmCo/Cr bilayer films for high-density recording media

The magnetic properties of a SmCo layer on a Cr underlayer, which was prepared by various Ar gas pressure ($P_{\mathrm{Ar}}$ ), were studied. A single line appeared in each X-ray diffraction diagram and its intensity became strong when $P_{\mathrm{Ar}}$ was decreased from 1.06 to 0.13 Pa. The microstructure observed by using atomic force microscopy showed that the surface morphological structure of Cr underlayers depended on $P_{\mathrm{Ar}}$ and the surface of the Cr underlayer became smoother as $P_{\mathrm{Ar}}$ was decreased, while the surface and the grain of the SmCo layer on the Cr underlayer were independent of $P_{\mathrm{Ar}}.$ The grain size of SmCo layers was as small as 30 nm with the surface roughness of about 1 nm. The coercivity, the squareness ratio, and the coercivity squareness ratio of the SmCo layer on the Cr underlayer prepared at 0.13 Pa were 155 kA/m, 0.92 and 0.92, respectively. Those values suggest that an easy axis of magnetization for the SmCo layer is in plane and the switching field distribution is very small. Although the crystal structure of the SmCo layer has not been clarified yet, it was found that the magnetic properties of SmCo layers can be controlled by the crystal structure of the Cr underlayer and SmCo/Cr bilayer films are promising materials for the ultrahigh density recording media.