Magnetism of nanostructured thin films

Nanostructured magnetic materials have unique properties that are different from bulk materials. They are of great scientific interest, as provide many potential applications. This thesis presents the structural and magnetic properties of FePt thin films and FePt-based nanocomposite thin films. FePt thin films were deposited by magnetron sputtering. By annealing the as-deposited films, high-anisotropy L10 FePt films were obtained. The fcc to fct phase transition is dependent on the annealing temperature and time, as well as the composition of the films. In slightly Fe-rich films, a certain degree of (001) texture has been observed. The magnetic properties are dependent on the degree of structure ordering of the films. The relationship between the coercivity and the long-range-order parameter has been investigated. Because of the high anisotropy energy of the L10 phase, FePt films with large coercivity have been obtained. High anisotropy films are potential candidates for extremely high-density magnetic recording media. High-density recording requires media with small grain size. In FePt films, the annealing processes may result in the unfavorable grain growth. Nanocomposite films FePt:SiO2 and FePt:B2O 3 have been fabricated with fine FePt L10 particles embedded in the SiO2 or B2O3 matrix. The presence Of SiO2 or B2O3 suppresses the grain growth, resulting in films with grain size less than 10 run. The structure and magnetic properties of these films are dependent on the processing temperatures and the FePt volume fractions, as well as the matrix materials. For the FePt:SiO 2 nanocomposite films, the required processing temperature is high and the FePt particles are mostly randomly oriented. However, in FePt:B2 O3 nanocomposite films, the processing temperature can be reduced to 500°C because of the low melting point of B2O 3, Furthermore, the easy axes of the FePt particles can be made either in the film-plane or in the film-normal direction, resulting in films with in-plane anisotropy or perpendicular anisotropy. The desired anisotropy direction, large anisotropy constant and coercivity, as well as fine grain size make these nanocomposite films promising candidates for high-density magnetic recording media