title: The relationship of the magnetic properties of M (M =  Mn, Fe, Co)-doped ZnO single crystals and their electronic structures.
abstract: The electronic density of states and magnetic properties were investigated by tunneling spectroscopy and SQUID, respectively, for a series of 3d transition-metal (Mn, Fe, Co)-doped ZnO. By tunneling spectroscopy an additional density of states was observed in Mn- and Co-doped ZnO adjacent to the top of the valence band of the host ZnO. Instead, in the Fe-doped sample, a band of density of states was observed across the Fermi level in the mid-gap. The magnetization curve (M versus H) obtained by SQUID showed a ferromagnetic hysteresis at room temperature for the Fe-doped sample, whereas for the Mn- and Co-doped samples, the M versus H curve showed only a linear characteristic without hysteresis. From the comparison of the density of states and the magnetization characteristics, it is strongly suggested that the ferromagnetism in Fe-doped ZnO at room temperature originates from the half-filled Fe 3d band in the mid-gap of the host ZnO.
authors.affiliation: Electrical Engineering and Bioscience, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Tamura
authors.forename: H
authors.initials: H
authors.lastname: Ozaki