Magnetic properties of He+-irradiated Pt/Co/Pt ultrathin films -: art. no. 064415

We have used ion irradiation to modify the perpendicular magnetic anisotropy and the magnetic coercivity of ultrathin Pt/Co(5 Angstrom)/Pt films without affecting their surface roughness. By studying the magnetization-reversal mechanisms at various temperatures, we show that ion irradiation does not alter the high lateral homogeneity of the films: magnetization reversal still occurs by very few nucleation events followed by easy domain-wall motion. We discuss the reason why irradiation actually reduces the density of sites effectively pinning the domain walls during magnetization reversal: the significant increase in domain-wall-propagation activation volume indicates that the defects created by irradiation are too densely packed to influence the domain-wall-propagation mode. We also show that ion irradiation reduces the Curie temperature and may lower it below 300 K. The temperature dependence of the magnetization of the films irradiated at fluences below 2 x 10(16) He+/cm(2) indicates a two-dimensional system with an Ising-type exchange Hamitonian. For higher irradiation fluences, the easy axis of magnetization tilts towards an easy cone and the films exhibit paramagnetic behavior at 300 K. The ability to adjust the magnetic technical properties via irradiation indicates that He+ irradiation could be of great interest for applications in thin-film magnetism.