Systematic investigation of anomalous Hall effect in Fe–Pt composition-spread epitaxial films for magnetic sensor application

Magnetic field sensors based on the anomalous Hall effect (AHE) require a magnetic thin film with high anomalous Hall resistivity (ρyxA) and moderate perpendicular uniaxial magnetic anisotropy (Ku) to achieve both a large linear sensitivity and a dynamic range (DR) adaptable for various applications. In this study, we fabricate Fe1−xPtx(0≤x≤1) composition-spread epitaxial thin films and systematically investigate the composition dependence of the AHE, aiming to achieve high sensitivity for the magnetic field sensors. We also explore the underlying physical mechanism of the AHE in the Fe–Pt binary system. Structural analysis reveals the [001]-oriented epitaxial growth, featuring distinct phases of A2-Fe, L12-Fe3Pt, L10-FePt, and L12-FePt3 as increasing x along with their mixed-phases, except for the Pt-rich region. Among the entire Fe1−xPtx, an off-stoichiometric Fe-rich composition Fe0.70Pt0.30 exhibits the highest ρyxA of 4.5 μΩ cm with a linear response to the external magnetic field and a DR of 600 mT, yielding a high sensitivity of 8 μΩ cm/T. The DR can be tuned in a wide range from 600 to 1400 mT by changing the Fe:Pt composition ratio, which is attributed to the variation in Ku and magnetization in the Fe–Pt binary alloy system. The anomalous Hall conductivity (AHC) shows an oscillatory variation with composition x, with the largest AHC of 1261 S/cm observed for Fe0.70Pt0.30. The theoretical calculation of the AHC for A2-Fe and L12-Fe3Pt, including the analysis of the density of states for the off-stoichiometric compositions, suggests that the overall variation in AHC with x can be mostly explained by an intrinsic mechanism and the electron doping effect introduced by Pt addition. Theoretical analysis supports that the highest sensitivity obtained in Fe0.70Pt0.30 originates from the large intrinsic AHC (1759 S/cm) predicted for L12-Fe3Pt.