Growth and Room Temperature Spin Polarization of Half-metallic Epitaxial CrO2 and Fe3O4 Thin Films

Abstract

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 theelectronic 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 (EF) theoretically predicted for HFMs can be confirmed experimentally. This article gives a short overview on the half-metallic ferromagnets with special emphasis on magnetite (Fe 3 O 4 ) and chromium dioxide (CrO 2 ). The spin-resolved electronic structure of thin epitaxial Fe 3 O 4 (111) and CrO 2 (100) films has been investigated at 293 K by means of spin-resolved photoemission spectroscopy (SP-PES). Epitaxial Fe 3 O 4 (111) films have been grown on different substrates by oxidizing epitaxial Fe(110) films. High surface quality and chemical homogeneity as well as high crystalline order in the bulk of Fe 3 O 4 (111) films were confirmed by means of STM and LEED. The Fe 3 O 4 (111) epitaxial films show a maximum spin polarization value of -(80′5)% near E F at 293 K confirming the half-metallic nature of Fe 3 O 4 in the [111] direction. High-quality epitaxial CrO 2 (100) films have been prepared by a chemical vapor deposition technique. Near E F an energy gap was observed for spill-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 CrO 2 .