Microstructure and magnetic properties of nanocomposite FePtCr-SiN thin films

Abstract

[(FePt) 100-xCr x] 100-δ-[SiN] δ nanocomposite thin films with x=0-25at.%, and δ=0-30vol.% were fabricated on a natural-oxidized Si(100) substrate by dc and rf magnetron cosputtering of FePt, Cr, and Si 3N 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 (TEM) and electron diffraction analyses indicated that the face-centered-cubic (fcc) γ-phase FePt, body-centered-cubic (bcc) 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 γ-FePt phase to the hard magnetic face-centered-tetragonal (fct) γ 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 x=10at.% and δ=15vol.%, 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. © 2002 American Institute of Physics.