Room Temperature Spin Polarization of Epitaxial Half-Metallic Fe3O4(111) and CrO2(100) Films

Abstract

The electronic structure of thin epitaxial films of magnetite (Fe3O4) and chromium dioxide (CrO2) has been investigated at 293 K by means of spin-and angle-resolved photoemission spectroscopy. Epitaxial Fe3O4(111) films have been grown on W(110) and Al2O3(1120) substrates by oxidizing epitaxial Fe(110) films. High surface quality and chemical homogeneity as well as high crystalline order in the bulk of Fe3O4 films were confirmed for both substrates by means of TEM, STM and LEED. The Fe3O4(111) epitaxial films show a maximum spin polarization value of −(80 ± 5)% near EF at 293 K. Two types of dispersive states were identified in the Γ-M direction of Fe3O4(111) surface Brillouin zone at 293 K by means of angle-resolved ultraviolet photoemission spectroscopy using synchrotron radiation. The surface electronic band structure of the Fe3O4(111) film is described as a product of two overlapping contributions following the symmetries of the oxygen sublattice surface Brillouin zone and the iron sublattice surface Brillouin zone, respectively. Epitaxial CrO2(100) films have been deposited on TiO2(100) substrates by a chemical vapor deposition technique. High structural quality of CrO2(100) films was confirmed by x-ray diffraction. The surface and the interface properties of the CrO2(100) films were studied by STM and TEM. Near the Fermi level an energy gap was observed for spin-down electrons and a spin polarization of about +(95 ± 10)% was found at 293 K.