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.

Effect of deposition temperature on the structure, magnetic and transport properties in Co2MnSi Heusler films

“…For amorphous S RT and S 300 , long-range crystallographic structure breaks, resulting in the small M S compared with the polycrystalline samples. Similar phenomena have also been reported by other group [34]. Interestingly, we found that there exists a dual behavior in magnetic moment at low magnetic fields for the polycrystalline samples.…”

“…According to the calculation of Kubler et al [33] on X 2 MnY Heusler alloys, the ferromagnetism of perfectly ordered CMS films (namely in L2 1 phase) comes from ferromagnetic Co-Co and Co-Mn sites interaction, and no nearest Mn-Mn sites exist in the L2 1 films. Therefore, the next-nearest Mn-Y-Mn indirect exchange dominates the ferromagnetic properties [34][35][36][37][38]. While in less ordered states (D0 3 , B2 or A2 phase), the appearance of anti-site disorder leads to the probable nearest Mn-Mn sites, which further results in the strong antiferromagnetic interaction, competing with the Co-Co and Co-Mn ferromagnetic interactions.…”

Two-magnon scattering by domain wall induced coupling in Co2MnGe/Au/Py layer systems

“…For the CoMnGe layers prepared at RT, we observe lower (220) BP intensities and an almost vanishing (440) peak. The BPs associated with (110) order (L2 and/or B2) do not imply that the entire sample is ordered, they signify only a fractional presence of such ordering in the samples . In that sense lower intensities of BPs for the RT grown Heusler layers indicate larger disorder of CoMnGe in comparison with the one prepared at 400C.…”

Investigations of the electronic and magnetic structures of Co2YGa (Y=Cr, Mn) Heusler alloys and their (100) surfaces

“…5 This alloy was found to exhibit a ferromagnetic behavior with a saturation magnetization of 5.1 l B /f.u. at 4 K. 6 However, the highest Curie temperature of 1100 K has been reported for Co 2 FeSi Heusler alloy, with a ferromagnetic half-metallic behavior and a total magnetic moment of 6.0l B /f.u. measured at 5 K. 7,8 Moreover, a theoretical study by Lee et al has predicted a half metallic behavior for Co 2 TiZ (Z ¼ Al, Si, Ga, Ge, and Sn) Heusler alloys.…”