Study of the Effect of Annealing on the Properties of Mn2RuxGa Thin Films

The effect of vacuum annealing thin films of the compensated ferrimagnetic half-metal Mn
₂
Ru
_x
Ga at temperatures from 250 °C to 400 °C is investigated. The 39.3 nm films deposited on (100) MgO substrates exhibit perpendicular magnetic anisotropy due to a small ~ 1% tetragonal elongation induced by the substrate strain. The main change on annealing is a modification in the compensation temperature T
_comp
, which first increases from 50 K for the as-deposited film to 185 K after annealing at 250 °C, and then falls to 140 K after annealing at 400 °C. There are minor changes in the atomic order, coercivity, resistivity, and anomalous Hall effect (AHE), but the net magnetization measured by SQUID magnetometry with the field applied in-plane or perpendicular-to-the-plane changes more significantly. It saturates at 20 -30 kA · m
^-1
at room temperature, and a small soft component is seen in the perpendicular SQUID loops, which is absent in the square AHE hysteresis loops. This is explained by the half-metallic nature of the compound; the AHE probes only the 4c Mn sublattice that provides the spin-polarized electrons at the Fermi level, whereas the SQUID measures the sum of the oppositely aligned 4c and 4a sublattice magnetizations.