Irradiation-induced electron tunnelling and small-polaron hopping in single-crystalline YIG

In electron (e - )-irradiated (>10 23 e - m -2 ) single crystalline yttrium-ion Garnet (YIG), after moderate annealing, low-temperature (T < 125 K) magnetic after-effect (MAE) spectra are observed which are of striking similarity to the well investigated spectra occurring in magnetite (Fe 3 O 4 ) below the Verwey transition (T V 125 K). Our analysis shows that this similarity is the result of corresponding relaxation mechanisms in both systems, i.e. electron tunnelling and small-polaron hopping. Deeper insights into these mechanisms are obtained from a thorough inspection of these spectra and their physical preconditions in the two, a-priori, completely different ferrimagnetic systems: (i) semiconductor, transformed into a quasi-insulating state due to long-range ionic ordering at low-temperatures (Fe 3 O 4 ) and (ii) insulator, brought into a state of low resistivity due to radiation-induced perturbations of the charge equilibrium (YIG).