Perpendicular magnetic anisotropy in a sputter deposited nanocrystalline high entropy alloy thin film

High entropy alloys (HEAs) have received great research attention in recent times because of their novel microstructures and properties. Among HEAs, eutectic HEA (EHEA) AlCoCrFeNi2.1 is considered particularly attractive because of its unprecedented mechanical properties. However, the functional properties of EHEA have been hardly explored. In the present work, we have investigated the magnetic properties of nanocrystalline EHEA films grown by RF magnetron sputtering in the as-deposited and after annealing at 200 °C, 400 °C, and 600 °C in vacuum. Further, the magnetic behavior was correlated with structural and chemical characteristics. Grazing incidence X-ray diffraction (GIXRD) of the films shows the presence of FCC and BCC phases similar to the target (bulk) material. Static and dynamic magnetic properties of the HEA films are investigated by using vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques, respectively. VSM results reveal the presence of the perpendicular magnetic anisotropy (PMA) in our films annealed at 600 °C, whereas the as-deposited and samples annealed at 200 °C and 400 °C exhibit only in-plane anisotropy behavior. The presence of PMA is further supported by the FMR dynamics results. The origin of PMA in sample annealed at 600 °C is attributed to the formation of Al2O3, which has been confirmed through GIXRD and amply corroborated by X-ray photoelectron spectroscopy (XPS). The interfacial hybridization effect between Co/Fe-3d and the adjacent O-2p orbitals of Al2O3 possibly resulted in PMA in HEA films.