Magnetic properties of Cd_1-xMn_xTe/C nanocrystals

Mn doped CdTe nanocrystals coated by carbon (Cd_1-xMn _xTe/C) were synthesized by a one-step, kinetically controlled solid state reaction under autogenic pressure at elevated temperatures. Electron microscopic analysis confirmed that the 40-52 nm Cd_1-xMn _xTe core was encapsulated by a 6-9 nm carbon shell. The efficient doping by Mn²⁺ in the zinc blende Cd_1-xMn_xTe lattice, up to an atomic ratio of Mn/Cd of 0.031, was confirmed from electron paramagnetic resonance (EPR) experiments. In the case of higher doping, it is likely that manganese is partially expelled to the nanocrystal surface. All the doped samples exhibit ferromagnetism at room temperature. The lowest doped sample has the highest magnetic moment (1.91 ± 0.02 μB/Mn). The more concentrated samples exhibit weaker ferromagnetic interactions, probably due to an incomplete coupling between carriers in the host CdTe semiconductor and dopant spins.