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Electron carrier-mediated room temperature ferromagnetism in anatase (Ti,Co)O2

Since the discovery of room temperature ferromagnetism in (Ti,Co)O2, the mechanism has been under discussion for a decade. Particularly, the central concern has been whether or not the ferromagnetic exchange interaction is mediated by charge carriers like (Ga,Mn)As. Recent two studies on the control of ferromagnetism in anatase (Ti,Co)O2 at room temperature via electric field effect [Y. Yamada et al., Science 332, 1065 (2011)] and chemical doping [Y. Yamada et al., Appl. Phys. Lett. 99, 242502 (2011)] indicate a principal role of electrons in the carrier-mediated exchange interaction. In this article, the authors review fundamental properties of anatase (Ti,Co)O2 and discuss the carrier mediated ferromagnetism.