Giant anomalous Hall effect in epitaxial Mn${}_{3.2}$Ge films with a cubic kagome structure

Abstract

We report on the first example of epitaxial Mn${}_{3+\hat{I}´}$Ge thin films with a cubic $L{1}_2$ structure. The films are found to exhibit frustrated ferromagnetism with an average magnetization corresponding to 0.98$\pm$0.06$\hat{I}{¼}_B$/Mn, far larger than the parasitic ferromagnetism in hexagonal Mn${}_3$Ge and the partially compensated ferrimagnetism in tetragonal Mn${}_3$Ge. The Hall conductivity is the largest reported for the kagome magnets with a low temperature value of $\ddot{I}{ƒ}_{xy}=1587$S/cm. Density functional calculations predict that a chiral antiferromagnetic structure is lower in energy than a ferromagnetic configuration in an ordered stoichiometric crystal. However, chemical disorder driven by the excess Mn in our films explains why a frustrated 120${}^{\circ }$ spin structure is not observed. Comparisons between the magnetization and the Hall resistivity indicate that a non-coplanar spin structure contributes the Hall signal. Anisotropic magnetoresistance and planar Hall effect with hysteresis up to 14 T provides further insights into this material.