Study on microscopic origin of spin excitation in TmFeO 3 by time-resolved multicolor optical pump-probe spectroscopy

Abstract

Spin dynamics of TmFeO 3 , mainly induced by two different mechanisms, were investigated by time -resolved multicolor pump -probe spectroscopy using femtosecond laser pulses. The spin dynamics, caused either by spin -reorientation phase transition or optical polarization -dependent effect, were distinguished by investigating their dependencies on external magnetic field and optical polarization. Spectral -dependent magneto -optic studies of the spin phase transition -induced spin dynamics revealed that laser -induced nonthermal exchange interaction between the electron states of iron (Fe 3+ ) and thulium (Tm 3+ ) ions is crucial for subsequent spin dynamics. This exchange interaction is influenced by the population change of the 4f electron states of Tm 3+ ions, making the spin wave generation highly dependent on crystal temperature. However, spectroscopic studies of the polarization -dependent spin dynamics show that they are only related to the 3d electrons of Fe 3+ ions, therefore, the spin dynamics appear to be a universal effect over a wide temperature range. Our observation can be further applied to study extended orthoferrite systems with other rare earth atoms.