Engineering of perpendicular magnetic anisotropy in half-metallic magnetic Heusler epitaxial thin films

Efficient spintronic devices based on thin films need a full spin polarization at Fermi energy, ultralow magnetic damping, and magnetization perpendicular to the film plane. ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Si}$ and ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Ge}$ half-metal magnets Heusler compounds are good candidates due to their minority spin gap that leads to fully polarized current and ultralow magnetic damping. However, their low magnetocrystalline anisotropy leads to in-plane magnetization. One way to get perpendicular magnetic anisotropy in such Heusler compounds is to grow them on ${\mathrm{Mn}}_{x}\mathrm{Ga}$- or ${\mathrm{Mn}}_{x}\mathrm{Ge}$-buffer layers with the ${\mathrm{D}0}_{22}$ structure for which a strong magnetocrystalline anisotropy was reported. Here we first analyzed the impact of the stoichiometry of these binary alloys on their magnetic properties where the largest magnetocrystalline anisotropy was observed for the 3:1 stoichiometry. The replication of this perpendicular magnetic anisotropy in several half-metal magnet Heusler compounds epitaxially grown on top of them was thus analyzed by using standard magnetometry but also x-ray magnetic circular dichroism and in situ magneto-optic Kerr effect measurements. Squared hysteresis loops needed for applications were obtained using ${\mathrm{Mn}}_{3}\mathrm{Ge}$ with a coercive magnetic field that can be tailored by varying the different thicknesses in the stack. Our results also allowed us to explain some reported magneto-optic Kerr effect results not yet understood.

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