Combinatorial exploration of rare-earth-free permanent magnets: Magnetic and microstructural properties of Fe-Co-W thin films

We have investigated the magnetic and structural properties of Fe-Co-W films using a composition spread technique. From the magnetometry measurements, large magnetization (900 emu^/cm3) and enhanced perpendicular coercive fields (2-3 kOe) of low W concentration films were observed. The synchrotron diffraction results show a structural transition from a crystalline to an amorphous state and the crystallization onset increases with increasing W concentration. The SEM and TEM characterizations show that the films with low W concentrations have vertically standing platelet-like grain structures which is ascribed to the enhanced coercive fields. Magnetometry studies indicate that as the W concentration increases, microstructural change results in evolution of magnetization reversal mechanism.