We study a diluted magnetic semiconductor system based on the spin of the ionized acceptor ${\mathrm{Cr}}^{+}$. We show that the negatively charged ${\mathrm{Cr}}^{+}$ ion, an excited state of the Cr in II-VI semiconductor, can be stable when inserted in a CdTe quantum dot (QD). The ${\mathrm{Cr}}^{+}$ attracts a heavy hole in the QD and form a stable hole-${\mathrm{Cr}}^{+}$ complex. Optical probing of this system reveals a ferromagnetic coupling between heavy holes and ${\mathrm{Cr}}^{+}$ spins. At low temperature, the thermalization on the ground state of the hole-${\mathrm{Cr}}^{+}$ system with parallel spins prevents the optical recombination of the excess electron on the $3d$ shell of the atom. We study the dynamics of the nanomagnet formed by the hole-${\mathrm{Cr}}^{+}$ exchange interaction. The ferromagnetic ground states with ${\mathrm{M}}_z=\pm 4$ can be controlled by resonant optical pumping and a spin relaxation time in the $20\mu \mathrm{s}$ range is obtained at $T=4.2$ K. This spin memory at zero magnetic field is limited by the interaction with phonons.

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• Dopants
• Optical & microwave phenomena
• Magnetic semiconductors
• Quantum dots
• Density functional calculations
• Magnetic techniques
• Photoluminescence