Ferromagnetic Transition in Diluted Magnetic Semiconductors

Abstract

A summary is given of recent theoretical works on effects of the RudermanKittel-Kasuya-Yosida (RKKY) interaction between the localized spins in various dimensionality systems of doped diluted magnetic semiconductors (DMS). Since this interaction is long-range, its influence on the temperature and magnetic field dependencies of magnetization and spin splitting of the bands is evaluated in the mean field approximation, but by taking into consideration disorder-modified carrier-carrier interactions. Theoretical evaluations show that the hole densities, which can presently be achieved, are sufficiently high to drive a paramagneticferromagnetic phase transition in bulk and modulation-doped structures of II-VI DMS. The results of recent magnetooptical studies on MBE-grown samples, containing a single, modulation-doped, 8 nm quantum well of Cd 1−x Mn x Te/Cd 1−y−z Mg y Zn z Te:N are shown to corroborate the theoretical expectations. These studies reveal the presence of a ferromagnetic transition induced by the two-dimensional hole gas. The transition occurs between 1.8 and 2.5 K, depending on the Mn concentration x, in agreement with the theoretical model.

Ferromagnetic Ordering in Diluted Magnetic Semiconductors

“…The main idea is that the ferromagnetic ordering is caused by the exchange interaction between magnetic impurities mediated by free electrons or holes [4,15]. This mechanism is commonly accepted now even though it does not explain the ferromagnetism at low density of carriers [10].…”