Anomalous Hall effect in Ni47.3Mn30.6Ga22.1/MgO(001) thin films

We investigate the temperature dependences of the magnetic properties, electrical resistivity, magnetoresistance, and Hall effect resistivity, ρH(H), in thin films of the Heusler-type Ni47.3Mn30.6Ga22.1 (at.%) magnetic shape memory alloys epitaxially grown onto a MgO(001) substrate. The results reveal martensitic transformation at about 230 K, premartensitic transition around 285 K, and the Curie temperature of austenite around 380 K. We obtained the coefficients of normal Hall effect (NHE), R0, and anomalous Hall effect (AHE), Rs, by fitting the total Hall resistivity curves ρH=R0Bz+4πRsMz in several magnetic field ranges (0.1–1, 0–5, 8–16, and 0–16 kOe), using experimental magnetization data. Both coefficients R0 and Rs strongly depend on the magnetic field. We also fit the Hall effect resistivity with the expression ρH=R0Bz+4πRsMz+ΔρH using the coefficients R0 and Rs obtained from the high-field interval (8–16 kOe), where the last term, ΔρH, was considered to correspond either to the topological Hall effect or to the antiferromagnetic Hall effect. The obtained temperature dependence and magnitude of ΔρH discard the presence of the skyrmions or antiskyrmions. We conclude that unconventional field dependences of the NHE and AHE coefficients are produced by the antiferromagnetic correlations and the influence of the magnetic field on the electronic structure.