Transition Metal-Doped Sb2Te3 and Bi2Te3 Diluted Magnetic Semiconductors.

Abstract

Motivated by the discovery of the ferromagnetic order in V-doped Sb2Te3 and Fe-doped Bi2Te3 bulk crystals, the study of the transition metal (TM) doped tetradymite-type semiconductors was extended to their thin film forms with the hope of significantly increasing the content of TM and thus enhancing the Curie temperature. High quality Sb2-xVxTe3 (x up to 0.35) and Sb2-xCrxTe3 (x up to 0.59) epitaxial films have been successfully prepared on sapphire (0001) substrates by non-equilibrium MBE growth technique, and their structural, transport and magnetic properties have been determined. Magnetization studies, Arrott plot analyses, and anomalous Hall effect measurements indicate that long range magnetic order persists to temperatures of at least 177K (in the case of Sb2-xVxTe3) and 190K (for Sb2-xCrxTe3). The observed carrier mediated, p-type favored ferromagnetic behavior supports a scenario of RKKY interaction with mean-field approximation. Bi2-xFexTe3 samples have also been prepared (for x up to 0.46), and they displayed n-type behavior and no signature of spontaneous magnetic ordering down to 2K. Trilayer structures with a normal Sb2Te3 layer sandwiched between two ferromagnetic Sb2-xCrxTe3 layers were fabricated in order to explore the influence of the interlayer exchange coupling mechanism (IEC). Such coupling was found to be present for small thickness of the spacer layer at low temperatures. Transition metal-doped tetradymite-type semiconductors represent a new class of diluted magnetic semiconductors that are octahedrally coordinated and that possess highly anisotropic structural and magnetic properties.