Ferromagnetism mediated by few electrons in a semimagnetic quantum dot

A (II,Mn)VI diluted magnetic semiconductor quantum dot with an integer number of electrons controlled with a gate voltage is considered. We show that a single conduction band electron is able to induce a spontaneous collective magnetization of the Mn spins, overcoming the short range antiferromagnetic interactions. The carrier mediated ferromagnetism in the dot survives at temperatures above 1 Kelvin, two orders of magnitude larger than the Curie temperature for the same material in bulk. The magnetic behavior of the dot depends dramatically on the parity of the number of injected electrons.