Tunneling evidence of half-metallicity in epitaxial films of ferromagnetic perovskite manganites and ferrimagnetic magnetite

Direct evidence of half-metallic density of states is observed by scanning tunneling spectroscopy of ferromagnetic La0.7Ca0.3MnO3 and La1-xSrxMnO3 (x=0.3,0.33) epitaxial films which exhibit colossal magnetoresistance (CMR). At 77 K, well below the Curie temperatures, the normalized tunneling conductance (dI/dV)/[I/V] for all samples exhibits similar pronounced peak structures, consistent with the spin-split density of states spectra for the itinerant bands in the ferromagnetic state. The exchange energy splitting between the majority and minority spins, as well as an apparent energy gap near the Fermi level, show variations with the chemical composition and the temperature. For comparison, the tunneling spectrum of a half-metallic ferrimagnet Fe3O4 is also studied. The characteristic spin-split density of states spectrum is observed, and the similarities and differences of Fe3O4 compared with the perovskite manganites are discussed. (C) 1998 American Institute of Physics. [S0021-8979(98)45811-0].