Scientists build 'magnetic semiconductors' one atom at a time

Yazdani cautioned that his team's technique would not translate immediately into new chip technology but would benefit fundamental research by providing a testbed for exploring magnetism in other semiconductors.

"We can now ask questions about these magnetic atoms and get answers," he said. "How does it affect the semiconductors' performance when you change their orientation, for example, or their distance from one another? Answers to these questions may allow us to link the electric current and magnetic spin within these new semiconductors, and that's a goal the field has been seeking for many years."

This research was funded in part by the National Science Foundation and the U.S. Army Research Office.

Abstract

Atom-by-Atom Substitution of Mn in GaAs and Visualization of Their Hole-Mediated Interactions

by D. Kitchen, A. Richardella, J.-M. Tang, M. E. Flatté, A. Yazdani

The discovery of ferromagnetism in Mn doped GaAs1 has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices2-4. A major hurdle for realistic applications of Ga1-xMnxAs, or other dilute magnetic semiconductors, remains their below room-temperature ferromagnetic transition temperature. Enhancing ferromagnetism in semiconductors requires understanding the mechanisms for interaction between magnetic dopants, such as Mn, and identifying the circumstances in which ferromagnetic interactions are maximized5. Here we report the use of a novel atom-by-atom substitution technique with the scanning tunnelling microscope (STM) to perform the first controlled atomic scale study of the interactions between isolated Mn acceptors mediated by the electronic states of GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn-Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga1-xMnxAs structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples. Our experimental methods also provide a realistic approach to create precise arrangements of single spins as coupled quantum bits for memory or information processing purposes.