O. Angelov

Perpendicular magnetization of FePt particles in silica induced by swift heavy ion irradiation

Particles of the FePt intermetallic compound with L10 structure embedded in silica films were submitted to irradiation by 120 MeV Au ions at different fluences. Observations by transmission electron microscopy evidenced an elongation of the particles, ascribed to an anisotropic ripening process during the thermal spikes occurring in the wake of the ions. However, the observed changes in the magnetic properties are attributed to the magnetostriction of the particles. Their compression by the matrix induces a tilt of easy magnetization axis from in-plane to perpendicular to the film surface, together with an increase in coercivity.

X-ray photoelectron study of high-energy He+ implanted a-SiC:H thin films

The implantation with high-energy He + ion beam results in modification of the optical band-gap and absorption coefficient of a-Si1-xCx:H films. X-ray photoelectron spectroscopy was used to characterize a-Si1-xCx:H thin films deposited by r.f. magnetron sputtering and implanted with high-energy He + ions. The non-implanted films show the expected variety of chemical bonds: silicon-silicon and silicon-carbon bonds, carbon being three- and fourfold coordinated. The X-ray and Raman spectra show that high-energy He + ion implantation leads to the introduction of additional disorder in the films. The X-ray photoelectron spectra of the implanted films show that, in addition to the already mentioned changes, the high-energy He + ion bombardment results in an increase of the threefold coordinated as compared to the fourfold coordinated carbon bonds, i.e. increased graphitization of the carbon content in the films. These structural modifications, due to the high-energy He + ion implantation, are the reasons for the observed changes in the optical properties of the films.