Thin films of the Heusler alloys Cu₂MnAl and Co₂MnSi: recovery of ferromagnetism via solid-state crystallization from the x-ray amorphous state

Abstract

X-ray amorphous thin films of the Heusler alloys Cu 2 MnAl and Co 2 MnSi have been prepared by magnetron sputter deposition at room temperature. In the amorphous state the Cu 2 MnAl phase is non-ferromagnetic; Co 2 MnSi is weakly ferromagnetic with a ferromagnetic Curie temperature of 170 K. By solid-state crystallization at high temperatures strong ferromagnetic order and high Curie temperatures are established in both alloys. The saturation magnetization of the Co 2 MnSi alloy reaches 5.1μ B /f.u. at 4 K, corresponding to 100% of the theoretical value; for Cu 2 MnAl we obtain 2.8μ B /f.u. at 4 K, which corresponds to 87.5% of the theoretical value. In samples of the Co 2 MnSi phase with optimum saturation magnetization Bragg reflections as indicators of a long-range chemical order are missing, whereas for the Cu 2 MnAl phase Bragg reflections confirm epitaxial quality and long-range L2 1 order.