Absence of topological Hall effect in FexRh100-x epitaxial films: Revisiting their phase diagram

A series of FexRh100-x (30 x 57) films were epitaxially grown using magnetron sputtering, and were systematically studied by magnetization, electrical resistivity, and Hall resistivity measurements. After optimizing the growth conditions, phase-pure FexRh100-x films were obtained, and their magnetic phase diagram was revisited. The ferromagnetic (FM) to antiferromagnetic (AFM) transition is limited at narrow Fe contents with 48 x 54 in the bulk FexRh100-x alloys. By contrast, the FM-AFM transition in the FexRh100-x films is extended to cover a much wider x range between 33% and 53%, whose critical temperature slightly decreases with increasing Fe content. The resistivity jump and magnetization drop at the FM-AFM transition are much more significant in the FexRh100-x films with similar to 50% Fe content than in the Fe-deficient films; the latter have a large amount of paramagnetic phase. The magnetoresistivity (MR) is rather weak and positive in the AFM state, while it becomes negative when the FM phase shows up, and a giant MR appears in the mixed FM and AFM state. The Hall resistivity is dominated by the ordinary Hall effect in the AFM state, while in the mixed state or high-temperature FM state, the anomalous Hall effect takes over. The absence of topological Hall resistivity in FexRh100-x films with various Fe contents implies that the previously observed topological Hall effect is most likely extrinsic. We propose that the anomalous Hall effect caused by the FM iron moments at the interfaces nicely explains the hump-like anomaly in the Hall resistivity data. Our systematic investigations may offer valuable insights into the spintronics based on iron-rhodium alloys.