Hydrogen absorption-induced rotation of magnetic anisotropy and tunable electrical transport in FePd alloy thin films

The magnetic behavior of Fe₄₀Pd₆₀ (FePd) alloy films undergoes a rotation of 90 ± 5 degrees within the surface plane upon hydrogen absorption. This phenomenon arises from the reversible modulation of the interplay between interfacial magnetic anisotropy energy (MAE) and volume MAE. The former is influenced by the regular atomic steps of the Al₂O₃(0001) substrate, while the latter is induced by oblique deposition, leading to a thin film composed of one-dimensional nanostructures. We systematically investigate the magnetism, crystalline structure, and electronic transport properties of FePd films, demonstrating that hydrogen charging significantly alters the dominant MAE, shifts the electron spin resonance peaks and enhances the saturation magnetization by 9.5 ± 1.0 %. The presence of hydrogen mediates electron transport, reducing the resistivity. The magnetoresistance (MR) behavior transitions from a combination of positive and negative MR behaviors to pure positive MR. Visualization of magnetic domain evolution through Kerr images elucidates the complex MR behavior, highlighting the competition between different MAEs. The physical changes in FePd can be detected through electronic signals, offering potential for practical applications, such as the ionic control of magnetic switching in memory or logic devices.