Nanoscale magnetic systems are attracting considerable attention due to their potential in the field of ultrahigh density recording media. To achieve high storage densities, assemblies of ferromagnetic particles with uniform and small size below 10 nm are required. However, as the magnetic bit size is further reduced to the superparamagnetic limit, the magnetization is easily perturbed by thermal agitation. Therefore, recent studies have been focused on FePt nanoparticle arrays owing to the existence of chemically ordered phases with exceptional magnetic properties such as large magnetocrystalline anisotropy constant.

We have used ion-beam sputtering to grow FePt thin films and C/FePt granular multilayers at room temperature. We have investigated the effects of thermal annealing on the structural and magnetic properties by combining the sensibilities of different techniques including TEM, RBS, GIXRD, GISAXS, and SQUID. We will show that the as-deposited films and granular multilayers contain FePt grains with a disordered fcc structure and are magnetically soft. Thermal annealing causes partial L1₀ ordering and growth of the FePt grains both in the FePt films and in the C/FePt multilayers, but these effects are restrained by the presence of carbon. We will demonstrate that thermal annealing of granular multilayers also results in the preferential graphitization of the carbon matrix and in the chemical interaction of the Fe atoms with the Si substrate. Magnetization measurements indicate that magnetic hardening occurs after annealing and that the saturation magnetization is strongly dependent on the annealing temperature.

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