Amplification of spin-filtering effect by magnetic field in GaAsN alloys

The effect of a longitudinal magnetic field on the optical spin orientation and spin-dependent recombination in dilute nitrides GaAsN has been studied for the first time. We have found that intensity I and circular polarization degree rho of the edge photoluminescence, excited in GaAsN alloys by circularly polarized light at room temperature, grow substantially in the longitudinal magnetic field B of the order of 1 kG. This increase depends on pump power, and, in the region of weak or moderate powers, the I and rho can reach a twofold value. We included the magnetic-field suppression of spin relaxation of the deep paramagnetic centers in the two-charge-state model, which considers the spin-dependent recombination of spin-polarized free electrons on the centers. The modified model describes qualitatively the rise of rho and I in a magnetic field under different pump intensities. Experimental dependences rho(B) and I (B) are shifted with respect to zero of the magnetic field by a value of similar to 200 G, while the direction of the shift reverses with change of the sign of circular polarization of pumping. As a possible cause of the discovered shift we consider the Overhauser field, arising due to the hyperfine interaction of an electron bound on a center with nuclei of the crystal lattice in the vicinity of the center.