Mn spin domains in highly photoexcited (Cd,Mn)Te/(Cd,Mg)Te quantum wells

Abstract

Direct spin and energy transfer between a dense two-dimensional electron-hole $(e\ensuremath{-}h)$ magnetoplasma and a Mn spin subsystem via $\mathrm{spd}$ exchange has been studied. Time-resolved photoluminescence spectra of the magnetoplasma excited by a powerful 10-ns laser pulse in a single ${\mathrm{Cd}}_{0.97}{\mathrm{Mn}}_{0.03}{\mathrm{T}\mathrm{e}/\mathrm{C}\mathrm{d}}_{0.75}{\mathrm{Mg}}_{0.25}\mathrm{Te}$ quantum well have been investigated in magnetic fields $B<~14 \mathrm{T}$ at helium temperature. A giant asymmetry of the plasma spin splitting has been observed in the spectra of dense homogeneously photoexcited plasma at high magnetic fields. This asymmetry has been explained in terms of formation of a domain structure within the magnetic subsystem, i.e., spatial stratification into regions with different Mn-spin temperatures. The Mn spin domains result from the Mn spin heating due to the direct spin-spin $\mathrm{sd}$ exchange between hot carriers and Mn via effective spin-flip scattering of electrons with simultaneous spin-flip of Mn. During the Mn spin heating under quasistationary excitation, first the Mn spin fluctuations grow and spin domains form, then the spin domain's volume increases. The spin domain's formation occurs due to resonant spin-flip scattering with a characteristic time $\ensuremath{\sim}1 \mathrm{ns}.$ The nonresonant Mn spin heating has been observed also with a characteristic time of $\ensuremath{\simeq}10 \mathrm{ns}.$