Interfacial Strain-Driven Large Topological Hall Effects in Supermalloy Thin Films with Noncoplanar Spin Textures

Materials exhibiting topological transport properties, such as a large topological Hall resistivity, are crucial for next-generation spintronic devices. Here, we report large topological Hall resistivities in epitaxial supermalloy (NiFeMo) thin films with [100] and [111] orientations grown on single-crystal MgO (100) and Al2O3 (0001) substrates, respectively. While X-ray reciprocal maps confirmed the epitaxial growth of the films, X-ray stress analyses revealed large residual strains in the films, inducing tetragonal distortions of the cubic NiFeMo unit cells. Magnetic force microscopy showed the presence of skyrmion-like features, which may arise from strain-induced spin texturing in the films. Magneto-optic Kerr effect confirmed a 4-fold magnetic anisotropy in the NiFeMo/MgO (100) film which exhibited a more pronounced topological Hall effect compared to that in the NiFeMo/Al2O3 (0001) film. We envisage that the strain-induced disruption of the centrosymmetry in the NiFeMo films possibly leads to Dzyaloshinskii-Moriya (DM) interactions within the spins. This gives rise to the skyrmion-like spin textures and notable topological Hall effects near room temperature hitherto unobserved in NiFeMo thin films. Theoretical simulations based on DM interactions strongly correlate the experimental results and corroborate with the presence of skyrmion-like spin textures in the films. The modulation of topology and magnetism in NiFeMo thin films through strain engineering may provide useful direction for the pursuit of quantum Hall effect based spintronic devices.