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