Magnetism in Ge_(1-x) Mn_(x) Thin Films andQuantum Dots Synthesized by Ion Implantation

摘要

Spin switching devices constructed using self-assembled magnetic Ge quantum dots are the ultimate goal of this effort. These devices are based on the manipulation of magnetic exchange between magnetic quantum dots and/or coherent spin states in the quantum dots. In this study, we introduced 1.1 atomic % of Mn ions into Ge thin films and 3 at.% Mn into Ge Quantum Dots by ion implantation in order to explore the ferromagnetism in Mn implanted Ge. In order to recrystallize the Ge and enhance the incorporation of Mn ions into the Ge lattice, rapid thermal annealing was applied following the implantation. A maximum saturation moment of 0.7 μ_B/Mn at 5 K was reached when the sample was annealed at 300°C and the moment decreased with higher annealing temperatures. The ferromagnetism in Mn:Ge thin films disappeared at ～15 K. However, superparamagnetism has been observed at 1 T up to 200 K for the 300°C annealed film and persisted to room temperature for the 400°C annealed film. Mn implanted Ge Quantum Dots were also found to be ferromagnetic at low temperatures and showed a superparamagnet transition around 200 K.