MAGNETIC-PROPERTIES OF AMORPHOUS NANOCOLUMNS CREATED BY HEAVY-ION IRRADIATION OF PARAMAGNETIC YCO2 THIN-FILMS (INVITED)

Recent studies have demonstrated the possibility of inducing amorphous latent tracks in metallic materials by GeV heavy ion irradiation. In the present work, 0.880 GeV U-238 beams have been used to induce ferro magnetic amorphous nanocolumns in nonmagnetic crystalline YCo2 films. The loss of crystallinity deduced by x-ray analysis is in good agreeme nt with the one determined by magnetic measurements. The Co magnetic m oment in the columns is approximately equal to 1 mu(B), as in bulk amo rphous YCo2, but the ordering temperature (150 K) is strongly reduced with respect to the bulk. Magnetization measurements reveal the nanoco lumns to be single domain. A perpendicular anisotropy is observed in s amples irradiated at the smallest fluencies, which is interpreted to b e due to shape anisotropy. A progressive decrease of the anisotropy wi th increasing fluence is observed and qualitatively described in terms of dipolar interactions between columns. At low temperature, the coer cive field reaches 650 Oe. A simple nonuniform magnetization reversal process is suggested.