Suppression of Electron Spin Relaxation in Mn-Doped GaAs

We report a surprisingly long spin relaxation time of electrons in Mn-doped $p$-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter, the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.

Figure 1

(a) PL spectra of the GaAs:Mn sample for different excitation powers as indicated in the panel. (b) Spectrally integrated PL intensity vs excitation power. (c) Intensity ratio $I_X/I_{\mathrm{Mn}}$ of the excitonic ($X$) and Mn lines vs excitation power. Solid lines in (b) and (c) are to guide the eye.

Figure 2

(a) A Hanle curve obtained from the nonmagnetically doped $p$-GaAs reference sample. (b) Hanle curves from the GaAs:Mn sample for various excitation power levels (indicated in the panel) detected at 1.41 (solid symbols) and 1.39 eV (open symbols). (c) Recovery of the spin polarization in an external magnetic field in Faraday geometry for $P=0.06$, 4.5, and 20 mW. Solid lines in (a) and (b) are fits to Eq. (2); those in (c) are fits to Eq. (3). In (b) and (c), the upper curves are offset vertically for clarity.

Figure 3

(a) Spin relaxation time ${\tau }_s$ vs excitation power $P$ for GaAs:Mn ($N_{\mathrm{Mn}}=8\times {10}^{17}{\mathrm{cm}}^{-3}$) (solid circles) and for $p$-GaAs containing nonmagnetic acceptors ($N_a=6\times {10}^{17}{\mathrm{cm}}^{-3}$) (open squares). (b) Lifetime $\tau$ and (c) correlation field $B_c$ vs $P$ for the GaAs:Mn sample.

Figure 4

(a) Hanle curves for two excitation powers (shown in the panel) measured at temperature $T=35\mathrm{K}$. (b) Spin relaxation times ${\tau }_s$ vs $T$ for the same excitation power levels as in (a). Solid lines in (b) are to guide the eye.