Effect of crystallographic orientation of Co_2MnGe Heusler-alloy film on its surface roughness and ordered structure

摘要

The effects of direction and degree of preferred orientation of Co_2MnGe film on the surface roughness and the ordered structure were investigated by utilizing various buffer layers and underlayers. Degrees of preferred orientation of Co_2MnGe film were estimated by measuring the full width at half maximum (FWHM) of the x-ray diffraction rocking curve for Co_2MnGe(400) or Co_2MnGe(220) reflections. A high B2 ordered structure and a high saturation magnetization, which is almost the same value as in the case of epitaxial Co_2MnGe films, were obtained regardless of the direction and degree of preferred orientation, except in the case of the Co_2MnGe films without both buffer layers and underlayers. Also, surface roughness decreased when decreasing the FWHM of x-ray diffraction rocking curve, and the small surface roughness (that is almost the same value as in the case of epitaxial Co_2MnGe films) was obtained for Co_2MnGe films with the high degree of preferred orientation. A smaller surface roughness was obtained in the case of Co_2MnGe films with (110) preferred orientation compared with the Co_2MnGe(100) case. The tendencies of change of the surface roughness were explained from the viewpoint of surface energy.