Ferromagnetism induced by free carriers in p-type structures of diluted magnetic semiconductors

An overview is given of studies aiming at elucidation of the dominant effects that control the character of magnetic ordering and the magnitude of carrier-mediated ferromagnetic interactions in various dimensionality structures of diluted magnetic semiconductors. The modulation-doped p-type quantum wells of Cd1−xMnxTe/Cd1−y−zMgyZnzTe:N as well as epilayers of Zn1−xMnxTe:N and of Ga1−xMnxAs grown at low temperatures are discussed as examples of systems, in which ferromagnetic correlation induced by free carriers is observed. The effect of kp and spin–orbit couplings, notably in heavily doped, strained or reduced-dimensionality systems, is addressed. It is pointed out that disorder and carrier–carrier interactions have a strong influence on the spin–spin interaction, particularly in the vicinity of the metal-to-insulator transition. Outstanding properties of low-dimensional spin systems, resulting from their tendency towards the formation of spin-density waves, are described in the context of the observed peculiar domain structure.