Influence of the Heat Treatment Atmosphere on Coercivity of [FePt/Au/FePt]2x Thin Films

FePt-based thin films are attractive materials for ultrahigh density magnetic recording application, due to their excellent magnetic properties [1-4]. However, for high coercivity provision, it is necessary to apply high temperature heat treatment to form ordered L10-FePt phase from initially disordered A1-FePt phase [5]. Particularly, it was determined that presence of H2 in inert annealing atmosphere leads to thermal stabilization of FePt films grains size and surface roughness [6]. [FePt(15 nm)/Au(7,5 nm)/FePt(15 nm)]2x thin films were deposited by dc magnetron sputtering onto thermally oxidized Si(100) substrates at room temperature, using FePt alloy (99,95 %) and Au (99,9 %) targets. Post-annealing of the film samples in temperature range of 500°C - 800°C was carried out in flowing Ar and Ar + H2 (3 vol.%) atmospheres for 30 s, using a fixed heating rate of 10°C/s. Structural properties of the as deposited and post-annealed films were investigated by the grazing-incidence wide-angle X-ray scattering (GIWAXS) method [7]. Magnetic properties were measured by superconductive quantum interference device-vibrating sample magnetometry (SQUID-VSM). It was founded, that H2 introduction into annealing atmosphere allows to reach high coercivity (21 kOe) after annealing at 600°C. Hydrogen presence leads to residual oxygen reduction from the heat treatment atmosphere and as a result to ordering process suppression. It was concluded that chemical ordering, texture formation of ferromagnetic grains, and its size in our case are not determining factors for provision of coercivity high values, because these properties were almost equal after annealing in both investigated atmospheres. Hydrogen incorporation into Au crystal lattice can lead to breaking of interatomic bounds and point defects formation. This effect could be related to acceleration of Au grain boundary diffusion into L10-FePt phase under mechanical stresses influence.