Effects of deposition temperature and quenching rate on the surface morphology and magnetic properties of FePt/TiN films

FePt thin films have been deposited on Si substrate with a TiN buffer layer. The effects of deposition temperature and the quenching rate on the magnetic properties and microstructure of the FePt/TiN films have been investigated. Out-of-plane anisotropy can be achieved for the film deposited at room temperature followed by annealing at 600 °C and quenching in air. It is observed that a small fraction of L10-FePt in the room temperature deposited film is well-aligned in the perpendicular direction which is due to the large surface energy of the TiN buffer layer, which contracts the lattice of L10-FePt during the ordering process. However, by increasing the deposition temperature from room temperature to 450 °C, both the L10-ordering parameter and the in-plane anisotropy can be enhanced. The microstructure and phase structural results indicate that a high quenching rate is beneficial to refine the FePt grains despite the high deposition temperature. The highest in-plane coercivity (915.6 kA/m) is obtained by depositing at 300 °C and quenching in air. However, when the film is deposited at 300 °C followed by quenching in ice water, the average FePt grain size dramatically decreases to 22 nm and the in-plane coercivity still maintains at about 875.8 kA/m. The results indicate that the high rate quenching can effectively separate the grains and result in the high coercivity due to the reduced exchange coupling effect.