Structure Of FePt Films Research Articles

The effect of Ag additives on the structure of Fe-Pt films

Homogeneous thin films of FePt and Fe-(Pt,Ag) were obtained by modernized three-electrode ion-plasma sputtering. The film thickness was 220–450 nm. In this case, the calculated cooling rate reached ~1012–1014 K/s. The structure of films was studied by X-ray diffraction and electron microscopy. It was found that nanocrystalline and amorphous phases were formed in freshly deposited films. It was shown that the resulting metastable structures were stable when heated to 670–890 K, depending on the composition. It was found that Ag additives reduced the coercive force of the films. It was shown that heat treatment increased the coercive force up to 36 kA/m in FePt films and up to 10 kA/m in Fe-(Pt,Ag) films. The conditions for obtaining films with low values of the temperature coefficient of electrical resistance (~1.1∙10-5 K-1) were determined.

Ordering and magnetic properties of FePt film with (001) texture

FePt films with a thickness of 25 nm were deposited by magnetron sputtering onto the MgO(001) substrates at 400℃, and subsequently annealed at temperatures (<italic>T</italic>_a) between 500℃-800℃ for 5 hours. The structures and magnetic properties of FePt films were analyzed by X-ray diffraction, vibrating sample magnetometer, and in-field magnetic force microscope. The as-deposited films show a (001) epitaxy induced by the MgO(001) substrates, but a disordered soft magnetic <italic>A</italic>1 phase. The ordering did not occur until <italic>T</italic>_a was raised up to 600℃. At <italic>T</italic>_a =600℃, the films changed into a mixture of soft <italic>A</italic>1 phase and hard<italic> L</italic>1₀ phase due to the partial <italic>A</italic>1→<italic>L</italic>1₀ transformation, and a special soft-hard phase composite with magnetic anisotropy can be obtained. The in-plane magnetization is mainly contributed by the soft phase with a coercivity exceeding 10 kOe; whereas the out-of-plane magnetization is dominant by the hard phase with a coercivity of about 5 kOe. These results indicate the existence of strong coupling between the soft and hard phases, leading to the formation of exchange springs. After annealing at 700℃, the structure of FePt films became almost ordered. The easy magnetization axis turned completely to the out-of-plane direction and a large coercivity higher than 20 kOe was observed. The atomic force microscope images show that the films treated at 700℃ are composed of island-like grains. Additionally, the in-field magnetic force microscope images indicates that most of grains initially having multiple domains change into single domain by domain wall displacing and vanishing at low field. The nucleation is supposed to be the main mechanism of magnetization reversal of grains.

The effect of a Bi underlayer on FePt thin film

In this paper, the FePt films with Bi underlayer were prepared by dc magnetron sputtering on glass substrates. The L10-FePt films were obtained after the deposited samples were subjected to vacuum annealing at various temperatures. The effect of a Bi underlayer on the ordering temperature and magnetic properties of FePt films was studied. Experimental results show that the FePt film can realize the low-temperature ordering at 350℃ after introduction of a Bi underlayer. Moreover, the Bi underlayer can also obviously enhance the coercivity Hc of the film and enlarge the concentration range of FePt films with high Hc. We studied the distribution of Bi atoms by X-ray photoelectron spectroscopy and the change of crystal structure of FePt films by X-ray diffraction. The cause of the above observatious is associated with enhanced ordering degree of FePt films by the Bi diffusion during annealing process.