Crystalline effect on ferromagnetism and magneto-transport of epitaxial semiconducting Co:ZnO films

We have studied the magnetic origin and the effect of crystallinity of epitaxial semiconducting Co:ZnO films on ferromagnetism and magneto-transport properties by comparing signal-type domain (SD) and twin-type domain (TD) structure films grown in the same conditions. A higher saturation magnetization in TD films than that in SD films is observed, suggesting that bound charge carriers, produced mainly by defects in films, play a dominant role in ferromagnetism. A lower concentration of itinerant carriers in TD films than that in SD films is detected, which helps separate the effects of bound and itinerant carriers on ferromagnetism and magneto-transport. We hypothesize the interaction of the spin moments of itinerant carrier with the bound carrier mediated ferromagnetic domain results in the weaker strength of the anomalous Hall effect in TD films than that in SD films. It is likely that both itinerant and bound carriers are important for spintronic application in diluted magnetic oxides and could be modified by control of crystal structure.