Role of Nb content in tailoring the microstructure and magnetic anisotropy of soft magnetic W/CoFeB alloy thin films prepared with varying the substrate temperature

The work describes the role of Nb addition on the magneto-structural properties of magnetron sputtered Si/SiO2/W/(CoFeB)1−xNbx (x = 0, 3, 5 and 10) metal metalloid alloy thin films. Films were grown at substrate temperature (Ts) of RT, 300 °C and 500 °C to realise the influence of Nb content in the amorphous and nano-crystalline states of (CoFeB)1−xNbx thin films. RT deposited films are soft magnetic (coercivity (Hc) ≤ 10 Oe), exhibits amorphous microstructure and display a well-defined uniaxial magnetic anisotropy (UMA) in the film plane. At 300 °C, devitrification occurs, and the film (x = 0) becomes partially crystalline with precipitation of FeCo nano-crystals, and UMA nearly disappears. With increasing Nb content, the mean grain size and amount of FeCo nano-crystals decreases, and partially crystalline CoFeB films transform to a completely amorphous microstructure with the simultaneous appearance of in-plane UMA and systematic improvement in soft-magnetic nature (Hc decreases from~22–5 Oe). Nb addition on at Ts= 500 °C results in grain growth inhibition and magnetically isotropic (CoFeB)1−xNbx films (except x = 3). The present study demonstrates that thermally stable amorphous CoFeB films with desired soft magnetic properties can be prepared by appropriate selection of Nb content and suitable growth temperature. •Preparation of amorphous and nanocrystalline Si/SiO2/W/(CoFeB)1-xNbx (x=0, 3, 5 and 10) alloy thin films.•Effect of the substrate temperature on magneto-structural properties of W/(CoFeB) 1-xNbx (x=0, 3, 5 and 10) alloy thin films.•Origin and evolution of in-plane magnetic anisotropy with Nb addition using diffraction measurements at a synchrotron source.•Correlation of Nb controlled microstructure CoFeB films with magnetic anisotropy.•Tuning of the microstructure and magnetic anisotropy soft magnetic CoFeB films with controlled Nb addition and growth temperature.