Giant anomalous Hall effect in epitaxial Mn3.2Ge films with a cubic kagome structure

We report on the first example of epitaxial Mn_3+δGe thin films with a cubic L1₂ structure. The films are found to exhibit frustrated ferromagnetism with an average magnetization corresponding to 0.98±0.060.16em0exB/Mn, far larger than the parasitic ferromagnetism in hexagonal Mn₃Ge and the partially compensated ferrimagnetism in tetragonal Mn₃Ge. The Hall conductivity is the largest reported for the kagome magnets with a low-temperature value of σxy=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^∘ spin structure is not observed. Comparisons between the magnetization and the Hall resistivity indicate that a noncoplanar spin structure contributes the Hall signal. Anisotropic magnetoresistance and planar Hall effect with hysteresis up to 14 T provides further insights into this material.