The work is devoted to definition of the phase composition formation regularities,
structure and magnetic properties in nanoscale Fe50Pt50-Au films and multilayered [Pt/Fe]n
(n = 1, 4, 8) compositions on SiO2(100 nm)/Si(001) and Al2O3 (1010) substrates at thermal
annealings.
It is established that by supervising of mechanical stresses level and their sign in
Fe50Pt50 layer by change of a thickness, location, quantity of additional Au layers and
annealing conditions (temperature, duration, speed of heating and atmosphere vacuum,
nitrogen, hydrogen) one can operate by ordering processes and phase compound
formation, structure and magnetic properties of film compositions. The variations in residual stresses/strains level and sign in the FePt layer of as-deposited films influense the change in the ordered L10-FePt phase formation temperature, structure and the coercivity in the film compositions. Increasing the level of compressive stresses in the Fe50Pt50 layer causes a decrease in the ordering temperature and improvement of the magnetic properties.
It is established that oriented grain growth with c-axis of easy magnetization in the [001] direction perpendicular to the film plane at annealing in vacuum occurs in films with a smaller thickness of the intermediate Au(7.5 nm) layer due to the higher level of compressive strains in the deposited films. Increasing the thickness of the Au layer to 15 nm and reducing the level of compressive deformations contributes to the growth of FePt grains with the c-axis of easy magnetization in the plane of the film. The same orientation can be achieved by increasing the thickness of the intermediate Au layer to 30 nm.
It is revealed, that application of hydrogen heat treatment accelerates
ordering
proce sses in Fe 50 Pt 50 /Au/Fe 50 Pt 50 fi lms in comparison with annealing in vacuum at the cost
of creation of additional compressi ve stresses caused by introduction of hydrogen atoms
in to L 1 0 FePt phase crystal lattice voids Thus the c-axis of easy magnetization in L10-FePt phase grains is located in the film plane. Hydrogen treatment allows to obtain higher values of coercivity (27.3 kOe) in Fe50Pt50/Au/Fe50Pt50 film compositions at a lower annealing temperature of 700 °C than at annealing in vacuum (900 °C), due to the intensive penetration of hydrogen atoms into the film.
It was determined that due to the action of the compressive stress during the diffusion of gold along the grain boundaries and the increase in the number of interfaces in films with an intermediate Au(7.5 nm) layer, the ordered L10-FePt phase formation temperature the can be reduced compared to the other Au layer location. In the films with various Au layer location (top, intermediate, under-) separated from the substrate, the same tendency of the A 1→ L 1 0 phase transformation temperature changing as in the films on the substrate is remained: the ordering temperature is lower in film with intermediate Au(7.5 nm) layer then in Au/Fe 50 Pt 50 and Fe 50 Pt 50 Au films
In this work it is also shown that the increase in the number of interfaces in [Pt/Fe]n film compositions, where n = 1, 4, 8, while maintaining the total film thickness, promotes the activation in diffusion processes and the formation of the disordered phase A1-FePt in the composition [Pt/Fe]4 and partially ordered regions with tetragonal distortions in the [Pt/Fe]8 composition already during deposition.
Rapid thermal annealing of [Pt/Fe]n film compositions (where n = 4, 8) on SiO2(100 nm)/Si(001) substrates in nitrogen atmosphere leads to the oriented growth of L10-FePt phase grains with a c-axis of easy magnetization, located in [001] direction, perpendicular to film plane.
The recommendations for controlling the stress state, the reduction of the temperature of the ordered L10-FePt phase formation, the obtaining of c-axis of easy magnetization oriented perpendicular or parallel to the film plane in the film based on FePt, application of which by thermal activated method will allow to increase the magnetic recording density and storage information were developed.
Key words: nanoscaled films, annealing, ordered L10-FePt phase, additional Au layer, coercivity.
