Transmission electron microscopy study of ion tracks in nanocrystalline Y$_3$Fe$_5$O$_{12}$

Transmission electron microscopy (TEM) was used to study the structural effects in nanocrystalline yttrium-iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG) induced by swift heavy ions (SHI). The nanopowder specimens were irradiated with Bi and Xe ions with energies from 230 to 670 MeV and fluences in the range of $2\times10^{11}$ to $5\times10^{12}$ ion/cm$^2$ with and without different thickness aluminium degraders. Ion impacts in nanoparticles induce the formation of amorphous cylindrical tracks similar to those previously observed in the bulk. The track size was found to be slightly larger in the vicinity of nanocrystals edges due to surface effects. The threshold energy loss for track formation was estimated in the range $4.6-6.92$ keV/nm, while no tracks were detected at $S_e$ lower than $4.6$ keV/nm. These results contribute to the understanding of radiation-induced damage processes in nanocrystalline materials and provide useful insight into track formation mechanisms in complex oxides under high electronic excitation.