Abstract

We describe the influence of local magnetization on electron localization in concentrated and diluted magnetic semiconductors. This includes a review of transport and optical evidence such as the magnetic-field-induced insulator metal transition in concentrated systems, i.e. Eu chalcogenides and Gd3-xvxS4 (where v = vacancy). It also includes a brief review of salient experimental evidence for polaron formation in the diluted magnetic semiconductor Cd1-xMnxTeiln. In addition, static and dynamic photo-induced magnetic measurements in ZnTe/Cd1-xMnxSe heterostructures are presented and their relevance to high-Tc materials discussed.

Introduction

This paper deals with the effects of local exchange due to interaction of carrier spins with the ionic spins in magnetic semiconductors. We are specifically concerned with the 4f shell of Gd3+ and Eu2+ (S) and the 3d shell of Mn2+ (S), which contribute to the magnetic character of the concentrated and diluted systems respectively. Towards this end, the body of the paper begins with a brief review of the relevant exchange mechanisms leading to polaron formation. In the concentrated systems, this leads to giant magneto-resistive effects in the Eu chalcogenides [1] and very distinctive luminescence [2]. It alsoleads to the spectacular magnetic-field-induced metal-insulator phase transition in the Gd3-xvxS4 compounds [3–5]. In the dilute system, polarons account for novel effects in spin-flip Raman scattering [6, 7] and low-temperature transport properties [8, 9], and for the best examples to date of photo-induced magnetism. The latter properties have been studied both by magneto-optical [10] and by very sensitive magnetic techniques [11, 12]. Furthermore, new femtosecond dynamic studies have given information about the formation and decay of the polarons themselves [10,12].