Magnetization Dynamics Down to a Zero Field in Dilute (Cd,Mn)Te Quantum Wells

The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in the absence of a static magnetic field was found to be up to 3 orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.

Figure 1

Spin-spin relaxation rate at 5 K ($+$), spin-lattice relaxation at 1.5–4.7 K ($\times$), adapted from Ref. 14, and present data at 1.5 K: fast and slow magnetization decay at 0 and 1 T, respectively (open symbols, carrier densities in the ${10}^{10}{\mathrm{cm}}^{-2}$ range; closed symbol, $3\times {10}^{11}{\mathrm{cm}}^{-2}$).

Figure 2

PL at at 1.5 K and $B=0$ for a QW with 0.6% Mn and $p\approx {10}^{10}{\mathrm{cm}}^{-2}$. (a) Spectrum. (b) Intensity vs time during a field pulse, at the wavelength marked with a vertical line in (a). (c) Magnetization dynamics (symbols), coil current (dotted line), and the result of calculations (solid and dashed lines) as described in the text.

Figure 3

Energy levels taking into account the hyperfine coupling, cubic crystal field, and mismatch strain.

Figure 4

(a) Magnetization decay in a sample with 0.8% Mn and $n\approx {10}^{10}{\mathrm{cm}}^{-2}$ at indicated values of the static magnetic field. (b) Magnetization decay in $n$-type and $p$-type ($p\approx 3\times {10}^{11}{\mathrm{cm}}^{-2}$) samples at 0 T.