Microstructure and magnetic properties of nanocomposite FePtCr–SiN thin films
Journal of Applied Physics
͓͑FePt͒ 100Ϫx Cr x ͔ 100-␦ -͓SiN͔ ␦ nanocomposite thin films with xϭ0 -25 at. %, and ␦ ϭ0 -30 vol. % were fabricated on a natural-oxidized Si͑100͒ substrate by dc and rf magnetron cosputtering of FePt, Cr, and Si 3 N 4 targets. The thickness of the films was kept at 10 nm in order to examine the possibility for applying in high-density magnetic recording media. Transmission electron microscopy ͑TEM͒ and electron diffraction analyses indicated that the face-centered-cubic ͑fcc͒ ␥-phase FePt,
... -centered-cubic ͑bcc͒ Cr, and amorphous SiN coexisted in as-deposited films. The as-deposited films were annealed in vacuum between 350 and 750 °C for 30 min, and then ice-water quench cooling, in order to transform the soft magnetic fcc ␥-FePt phase to the hard magnetic face-centered-tetragonal ͑fct͒ ␥ 1 phase. Cr was added to inhibit the FePt grain growth, and was observed by TEM and energy disperse spectrum analysis in the grain surface area of FePt grains. The TEM observation indicated that the structure of the film was an amorphous SiN matrix with FePtCr particles dispersed in it. The particle size of FePtCr in annealed film was increased with the annealing temperature but decreased with the increase of SiN and Cr contents. Magnetization measurements indicated that the optimum condition for high-density magnetic recording purpose of the film was found with xϭ10 at. % and ␦ϭ15 vol. %, annealing at 600 °C for 30 min. The average grain size of the FePtCr in this film is about 9.5 nm, the saturation magnetization is 450 emu/cm 3 , in-plane coercivity is 3.7 kOe, and in-plane squareness is about 0.75.