Growth and room temperature spin polarization of half-metallic epitaxial CrO2 and Fe3O4 thin films

Potential applications of systems based on half-metallic ferromagnets (HMFs) in magneto- and spinelectronics including spin injectors, magnetic field sensors and magnetic memory devices stimulated the investigation of the electronic properties of HFMs by a multitude of experimental and theoretical approaches. The main question remains however if the 100% spin polarization at the Fermi level (E-F) theoretically predicted for HFMs can be confirmed experimentally. This article gives a short overview on the half-metallic ferromagnets with special emphasis on magnetite (Fe3O4) and chrornium dioxide (CrO2). The spin-resolved electronic structure of thin epitaxial Fe3O4(111) and CrO2(100) films has been investigated, copy (SP-PES). Epitaxial 293 K by means of spin-resolved photoemission spectroscopy ial Fe3O4(111) films have been grown on different substrates by oxidizing epitaxial Fe(110) films. High surface quality and chemical hornogeneity as well as high crystalline order in the bulk of Fe3O4(111) films were confirmed by means of STM and LEED. The Fe3O4(111) epitaxial films show a maximum spin polarization value of -(80 +/- 5)% near E-F at 293 K confirming the half-metallic nature of Fe3O4 in the [111] direction. High-quality epitaxial CrO2(100) films have been prepared by a chemical vapor deposition technique. Near EF an energy gap was observed for spin-down electrons and a. spin polarization of about +(90 +/- 10)% was found at 293 K by means of SP-PES. This value and the magnitude of the gap in the minority spin channel are in good agreement with the prediction of the half-metallic nature of CrO2.