Magnetic ordering in doped semiconductors near the metal-insulator transition

Experiment clearly shows a certain extent of ordering of localized magnetic moments in doped semiconductors near the metal-insulator transition. An antiferromagnetic spin glass structure is revealed in a number of n-type materials (Ge:As, 6H- and 4H-SiC:N) by Electron Spin Resonance spectroscopy as a sharp decrease in the density of paramagnetic centres, observed when approaching the transition from its insulator side. In a p-type material (Ge: Ga), the macroscopic magnetization and residual magnetization, as well as hole coupling in pairs or clusters with uncompensated moment, follow from the recently discovered hysteresis of variable range hopping magnetoresistance, accompanied by sharp drops in resistance on reversing the magnetization of the system. The location of the magnetically ordered phases is established. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.