Giant anomalous Hall effect in epitaxial Mn_3.2Ge films with a cubic kagome structure

We report on the first example of epitaxial Mn_3+δGe thin films with a cubic L₁₂ structure [1]. The films are found to exhibit frustrated ferromagnetism with an average magnetization corresponding to 0.98 ± 0.06 μ_B /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 σ_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 in part 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. A combination of Monte Carlo simulations and DFT calculations are used to explain the anomalous behavior in this material

[1] J. S. R. McCoombs, et al. Phys. Rev. B 110, 064401 (2024).