Depth-Profiling Magnetic Interfaces Formed Intrinsically in FePt₃ by Ion-Beams

Using ion-beams to locally modify material properties is rapidly gaining momentum as a technique of choice for the fabrication of magnetic nano-elements because the method provides the capability to nano-engineer in 3D, which is important for many future spintronic technologies. The precise definition of the resulting element shape is crucial for device functionality. In this work, the intrinsic sharpness of a magnetic interface formed by nano-machining FePt₃ films using He⁺ irradiation is investigated. Through careful selection of the irradiating ion’s energy and fluence, ferromagnetism is locally induced into a fractional volume of a paramagnetic (PM) FePt₃ film by modifying the chemical order parameter. Using a combination of magnetometry, transmission electron microscopy and polarised neutron reflectometry it is demonstrated that the interface over which the PM to ferromagnetic modulation occurs is confined to a few atomic monolayers only. Using density functional theory, the mechanism for the ion-beam induced magnetic transition is elucidated and shown to be caused by an intermixing of Fe and Pt atoms in anti-site defects above a threshold density.