Tunneling evidence of half-metallicity in epitaxial films of ferromagneticperovskite 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). A t 77 K, well below the Curie temperatures, the normalized tunneling conduct ance (dI/dV)/[I/V] for all samples exhibits similar pronounced peak structu res, consistent with the spin-split density of states spectra for the itine rant bands in the ferromagnetic state. The exchange energy splitting betwee n the majority and minority spins, as well as an apparent energy gap near t he Fermi level, show variations with the chemical composition and the tempe rature. For comparison, the tunneling spectrum of a half-metallic ferrimagn et Fe3O4 is also studied. The characteristic spin-split density of states s pectrum 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].