The discovery of ferromagnetism in Mn doped GaAs [1] has ignited interest inthe development of semiconductor technologies based on electron spin and hasled to several proof-of-concept spintronic devices [2-4]. A major hurdle forrealistic applications of (Ga,Mn)As, or other dilute magnetic semiconductors,remains their below room-temperature ferromagnetic transition temperature.Enhancing ferromagnetism in semiconductors requires understanding themechanisms for interaction between magnetic dopants, such as Mn, andidentifying the circumstances in which ferromagnetic interactions are maximized[5]. Here we report the use of a novel atom-by-atom substitution technique withthe scanning tunnelling microscope (STM) to perform the first controlled atomicscale study of the interactions between isolated Mn acceptors mediated by theelectronic states of GaAs. High-resolution STM measurements are used tovisualize the GaAs electronic states that participate in the Mn-Mn interactionand to quantify the interaction strengths as a function of relative positionand orientation. Our experimental findings, which can be explained usingtight-binding model calculations, reveal a strong dependence of ferromagneticinteraction on crystallographic orientation. This anisotropic interaction canpotentially be exploited by growing oriented Ga1-xMnxAs structures to enhancethe ferromagnetic transition temperature beyond that achieved in randomly dopedsamples. Our experimental methods also provide a realistic approach to createprecise arrangements of single spins as coupled quantum bits for memory orinformation processing purposes.
展开▼
