Field-free magnetic rotation in FePd alloy films controlled by reversible hydrogenation

In this study, we performed magneto-optical Kerr effect (MOKE) microscope measurements and X-ray diffraction to examine the hydrogenation effect on the magnetic anisotropy (MA) of Fe₄₀Pd₆₀/Al₂O₃ thin films and its correlation with crystalline structure. The change in magnetic coercivity was observed and attributed to the rotation of MA, which is characterized by the azimuthal angle-dependent MOKE. Hydrogen-enhanced magnetic moment was confirmed by X-ray magnetic circular dichroism. Multi-step etching processes were used to lower the thickness of the FePd alloy coating, and the hydrogenation process triggered the magnetic easy axis to always be parallel to the same direction. The magnetic anisotropy energy (MAE) of FePd film originates from the volume and the interface-contributed MAE. When the MAEs prefer different orientations, the film thickness and the hydrogen absorption will change the dominant term, resulting in the MA rotation. Furthermore, the reversible rotation of magnetism was achieved through hydrogen absorption and desorption without an external magnetic field. These observations are applicable to the development of field-free switched spintronic devices.