Co_<i>x</i>Cu_1–<i>x</i>Cr₂S₄ Nanocrystals: Synthesis, Magnetism, and Band Structure Calculations

Abstract

Spin-based transport in semiconductor systems has been proposed as the foundation of a new class of spintronic devices. For the practical realization of such devices, it is important to identify new magnetic systems operating at room temperature that can be readily integrated with standard semiconductors. A promising class of materials for this purpose is magnetic chromium-based chalcogenides that have the spinel structure. Nanocrystals of Co_<i>x</i>Cu_1–<i>x</i>Cr₂S₄ have been synthesized over the entire composition range by a facile solution-based method. While CuCr₂S₄ is a ferromagnetic metal, CoCr₂S₄ is known to be a ferrimagnetic semiconductor. Systematic changes in the lattice parameter, size, and magnetic properties of the nanocrystals are observed with composition. The nanocrystals are magnetic over the entire range, with a decrease in the magnetic transition temperature with increasing Co content. Band structure calculations have been carried out to determine the electronic and magnetic structure as a function of composition. The results suggest that ferrimagnetic alignment of the Co and Cr moments results in a decrease in magnetization with increasing Co concentration