A thermal spike model for nanophase formation in yttrium iron garnet under swift heavy ion beams

Amorphous latent tracks can be produced in the magnetic insulators, like yttrium iron garnet (Y3Fe5O12 or YIG), by irradiations with swift heavy ions in the electronic slowing down regime. For this, the electronic stopping power must be higher than a threshold, around 4.0 keV nm(-1) in the case of YIG, to obtain the amorphization of the material, when the irradiation proceeds with heavy ions in the 0.8-6 MeV amu(-1) range. In the same energy range, we find that a nanophase can be formed in YIG by track overlapping. This occurs at fluences depending on the electronic stopping power, and corresponding to the random impacts of the heavy ions on the amorphous tracks. Yet, no subsequent amorphization of the nanophase is observed even at high fluences. These results are interpreted with a model based on the thermal spike induced by the high density of ionizations and electronic excitations in the material.