Optically induced magnetization and ultrafast spin relaxation in manganese oxide

Abstract

The optically induced magnetization and ultrafast spin relaxation in an antiferromagnet MnO were observed by polarization spectroscopy with the pump-probe technique. The spin relaxation time in the picosecond region was measured at temperatures from 6 up to 800 K. The observed spin relaxation is the sum of the spin-spin relaxation and the spin-lattice relaxation. At lower temperatures below room temperature, the temperature-independent spin-spin relaxation is dominant. A stepped decrease in the spin relaxation rate was observed near the N\'eel temperature ${T}_{N}=118\text{ }\text{K}$, where the long-range order is lost. At higher temperatures above room temperature, the temperature-dependent spin-lattice relaxation is dominant. The observed spin-lattice relaxation rate has a ${T}^{2}$ dependence instead of the ${T}^{9}$ dependence well known in magnetic-resonance measurements for the Raman process of phonons. The observed temperature dependence can be explained by the conventional theory of spin-lattice relaxation for the Raman process by taking account of the effect of the Debye temperature of the crystal.