Resistivity Decrease Due to Ferromagnetic Resonance in EuO

The d.c. transport properties of EuO at ferromagnetic resonance (FMR) have been studied in the liquid helium temperature range at 24 GHz microwave frequency in samples with d.c. resistivities ρd.c. (4.2 K) = 103-106 Ω-cm. A decrease in ρd.c. was found at FMR. This decrease was largest in a sample with ρd.c. (4.2 K) = 3.3 × 104 Ω-cm and it was strictly proportional to the microwave power absorbed by the sample. The experimental results are explained on the basis of the spin energy transfer model in which two different electronic systems, that is, the localized 4f-electrons being responsible for the FMR and mobile band electrons contributing to the resistivity are assumed. The microwave energy absorbed by 4f-electrons is transferred to the free charge carriers through their mutual interactions and it turns out to give an increase in the kinetic energy of carriers and accordingly an increase in their mobilities. This model explains reasonably well the order of magnitude of the observed changes in ρd.c. and gives an estimate for the energy relaxation time of carriers τepsilon = 3.0 × 10-13 s.