Novel metal-carbon(60) nanocrystalline magnetic thin films
Barrera, Enrique V.
Doctor of Philosophy
A novel type of nanocrystalline magnetic thin films consisting of ferromagnetic metals and C60 have been developed and investigated. CO-C 60, Fe-C60 and CoFe-C60 with different concentrations of C60 thin films have been manufactured by thermal vapor codeposition. The microstructures and magnetic properties of the films can be significantly enhanced by varying the concentrations of C60 in the films. The stability of C60 and the compatibility of C60 with the metallic matrices are confirmed by mass spectrometry, Raman, WDS, XRD and TEM. Strong metal-C60 interaction is indicated by higher desorption temperatures of C60 in the meta-C60 films than that in pure C60 and the peak shift in Raman spectra. TEM shows that the grain size of the matrix metal decreases proportionally with increasing C60 concentration. Nanosize uniform columnar grains with nanoscale dispersion of C60 on the grain boundaries are commonly observed in the metal-C60 films. A self-assembly grain growth model based on the size effect of C60 and the metal-C60 interaction is proposed to delineate the microstructural evolution by C60. Calculations based on this model are consistent with experimental observations and give a grain size vs. C60 (carbon) concentration relationship. Grain growth retardation by C60 is observed in a CO-C60 film. Out-plane magnetic remanence and coercivity are enhanced in both the CO-C60 and Fe-C60 films. In the in-plane direction, the coercivity deceases in CO-C60 films but increases slightly in Fe-C60 films with increasing C60 concentrations. In-plane magnetic anisotropy is detected in CO-C60 films but not in Fe-C60 films. Strong temperature-dependent magnetization remanence and saturation are found in both the Co-C60 and Fe-C60 films with high C60 concentrations due to the nanosize grain effects. Temperature effects on the coercivity of CO-C60 and Fe-C60 are different and determined by the intrinsic magnetocrystalline anisotropy energy. Coercivity of the CoFe-C60 films increases after annealing above 450°C. An unusual magnetization behavior of the virgin curve intersecting with the major hysteresis loop and fast magnetic switch is observed in a Fe 83C60 film. The magnetic properties are interpreted by MOIF technique and correlated to the film microstructure.
Physics; Electromagnetics; Metallurgy; Engineering; Materials science