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Hole-Cr+ nanomagnet in a semiconductor quantum dot

We show that the negatively charged Cr+ ion, an excited state of Cr in II-VI semiconductors, can be stable when inserted in a CdTe quantum dot. The Cr+ attracts a hole and forms a hole-Cr+ spin complex with a ferromagnetic coupling. The resulting hole-Cr+ nanomagnet can be controlled optically. The ferromagnetic ground states with total spin Mz=±4 are prepared by resonant optical pumping and a spin memory in the 20 µs range is obtained at 4.2K and zero magnetic field