Photoinduced magnetization wave in diluted magnetic semiconductors

摘要

We derive an evolutional equation incorporating the processes of spin-polarization transfer from an electron to a magnetic ion subsystem of a diluted magnetic semiconductor along with spin-lattice relaxation and spatial spin diffusion. Above equation has been obtained for nonequilibrium magnetization due to exchange scattering of photoexcited charge carriers by magnetic ions. We show that the mechanism of a band gap narrowing due to exchange scattering requires relatively low optical power to reach an optical bistability for pump frequency range close to crystal band gap. In a bulk crystal, only relatively small local area with essential magnetization enhancement can absorb optical power, thus forming a photoinduced magnetization wave. Spatial spin diffusion can be responsible for a motion of such magnetization wave. We solve above derived equation both analytically for one-dimensional case and numerically otherwise and perform its stability analysis. We also evaluate numerically possible threshold of photoinduced magnetization wave excitation for typical diluted magnetic semiconductor A1-xIIMnxBVI and estimate its length and velocity of propagation.