Hole- Cr+ nanomagnet in a semiconductor quantum dot

Here, the authors 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 nanomagnet can be controlled optically. The ferromagnetic ground states, with total spin ${M}_z$ = \ifmmode\pm\else\textpm\fi{}4, are prepared by resonant optical pumping and a spin memory in the 20 \textmu{}s range is obtained at 4.2 K and zero magnetic field.