Presence of antisite disorder and its characterization in the predicted half-metalCo2MnSi

The Heusler alloy ${\mathrm{Co}}_2\mathrm{MnSi}$ is predicted to be a half-metallic ferromagnet and thus is considered a promising candidate for incorporation into spintronic devices. Recent theoretical calculations have shown that antisite disorder of a few percent in some Heuslers can destroy half metallicity, emphasizing the importance of characterizing samples for disorder. In this work we compare the magnetic, structural, and transport properties of ${\mathrm{Co}}_2\mathrm{MnSi}$ for bulk single-crystal boules, polycrystalline arc-melted buttons and polycrystalline thin films. The lattice parameter, coercivity, and saturation magnetization of the single-crystal and arc-melted samples are statistically identical. On the other hand, the residual resistivity ratio ${\rho }_{300\mathrm{K}}/{\rho }_{5\mathrm{K}}$ shows sharp contrasts, with the single crystal and the arc-melted button having ratios of 6.5 and 2.7, respectively. Neutron-diffraction experiments show that the antisite disorder for the arc-melted samples is zero for Mn-Si antisite disorder, but between 10 and 14 % for Co-Mn antisite disorder. We postulate this to be the cause for the increased amount of defect-induced scattering in the electrical transport measurements of the arc-melted samples. The thin films, similarly, have lattice constants, magnetic properties, and room-temperature resistivities that approach those of the single crystal. The best films, however, have residual resistivity ratios of 1.4. By comparing these films to single crystalline thin films grown in other studies, we again find evidence supporting Co-Mn antisite disorder as the primary scattering mechanism.