Optical Orientation of Mn$^{2+}$ Spins in Bulk (Zn, Mn)Se Induced by Magnetic Field

N. V. Kozyrev, K. A. Baryshnikov, B. R. Namozov, I. I. Kozlov, M. E. Boiko, N. S. Averkiev, Yu. G. Kusrayev

Published 2024-10-12Version 1

The optical orientation of Mn$^{2+}$ spins in the first excited state $^4$T$_1$ was experimentally observed in bulk (Zn, Mn)Se ($x_\mathrm{Mn}=0.01$) in the an external magnetic field of up to $6\,$T in Faraday geometry. This occurred during quasi-resonant continuous wave circularly polarized photoexcitation of the intracenter d-d transitions. A non-monotonic dependence of the thermal circular polarization of the intracenter photoluminescence on the magnetic field was observed. A theoretical model is proposed to describe the selection rules for resonant optical d-d transitions of an isolated Mn$^{2+}$ ion in a ZnSe cubic crystal. These rules are based on the analysis of the total angular momentum symmetry for the ground ($^6$A$_1$) and first excited ($^4$T$_1$) states of the Mn$^{2+}$ ion. This discussion neglects the specific mechanism for spin-flip processes in a d-shell of the ion during optical excitation. The analysis is founded on the rotational symmetry of the effective total angular momenta and parity for each state as a whole. Additionally, the Jahn-Teller coupling of the excited state orbital parts with tetragonal ($e$-type) local distortions of the crystal lattice is considered. This coupling results in the segregation of cubic axes and spin projections on these axes due to weak spin-orbit and spin-spin coupling in the excited state. This leads to energy splitting for spin states with their projections of $\pm 1/2$ and $\pm 3/2$ on each axis distinguished by specific Jahn-Teller distortion in the corresponding atomic potential minimum. By introducing two different times of relaxation to reach thermodynamic equilibrium for $\pm 1/2$ and $\pm 3/2$ states in each Jahn-Teller configuration, an angle dependent optical orientation contribution in photoluminescence polarization arises in the presence of a magnetic field.