SWIFT HEAVY-IONS IN MAGNETIC INSULATORS - A DAMAGE-CROSS-SECTION VELOCITY EFFECT

The damage in ferrimagnetic yttrium iron garnet, Y3Fe5O12 or YIG, induced by energetic heavy-ion bombardment in the electronic stopping-power regime has been studied in the low-velocity range (for a beam energy E less-than-or-equal-to 3.6 MeV/amu). Epitaxial thin films of YIG on [111]-Gd3Ga5O12 substrates were thus irradiated at room temperature with 15-MeV F-19, 50-MeV S-32, 650-MeV Ta-181, 750-MeV Pb-208, and 666-MeV U-238. The damage-cross-section A is extracted from channeling-Rutherford-backscattering spectroscopy and compared to previous works. All the experimental results show that at one given value of dE/dx, the damage cross section is higher for low-velocity ions than for high-velocity ions over a large range of dE/dx. At constant dE/dx, the larger the difference between the ion velocities is, the larger the difference between the damage cross sections. Such a deviation might be explained by the effect of the energy deposition being more localized for the low-velocity ions than for the high-velocity ions. This work clearly indicates that the electronic stopping power is not the only key parameter in the creation of ion tracks, and that the damage cross section depends on the lateral distribution of the energy deposition.