Nano Letters 11, 2584–2589 (2011)

(Ga,Mn)As is the model ferromagnetic semiconductor, used to demonstrate prototype devices that merge the suitability of semiconductors for electronics with magnetism. Unfortunately the Curie temperature TC has never gone beyond 190 K, a real obstacle for the material to become mainstream. Lin Chen et al. have now increased TC to 200 K by making (Ga,Mn)As nanowires. The main problem so far has been doping with Mn atoms. The more Mn is introduced to substitute Ga, the higher TC, in principle. However, beyond a certain threshold Mn atoms locate between Ga atoms rather than substituting them, which in fact decreases TC. A way to get rid of interstitial Mn atoms is to diffuse them out by thermal annealing. By patterning their material in nanowires, Lin Chen and colleagues have increased the surface available for the interstitial to diffuse out. They increased TC from an original 160 K to 200 K, but it may go even higher. It may not always be true, but in this case going to the nanoscale certainly helps.