Growth and magnetotransport study of thin ferromagnetic CrO₂films

Abstract

Highly a-axis-textured CrO 2 films have been deposited on Al 2 O 3 (0001) and on isostructural TiO 2 (100) substrates by a chemical vapour deposition technique. For Al 2 O 3 substrates a columnar growth of CrO 2 (010) on an initial Cr 2 O 3 (0001) layer has been found in transmission electron microscopy as well as in x-ray diffraction investigations. The sixfold in-plane symmetry of a (0001)-oriented Cr 2 O 3 initial layer leads to three equivalent in-plane orientations of the CrO 2 unit cell as confirmed by electron diffraction and scanning electron microscopy. The growth can be understood by a simple model of the in-plane symmetries of the Al 2 O 3 (0001), Cr 2 O 3 (0001), and CrO 2 (010) lattices. The growth on TiO 2 (100) substrates leads to (100)-oriented CrO 2 films of higher crystalline quality than the ones grown on Al 2 O 3 (0001). Transmission electron microscope images show growth of CrO 2 (100) directly on the TiO 2 (100) substrates and no significant Cr 2 O 3 inclusions within the CrO 2 (100) layer. All contributions to the magnetoresistance (MR) due to anisotropic MR, Lorentz MR, spin disorder, and intergrain tunnelling MR have been determined and partly correlated with the crystalline properties of the samples investigated. For films of both types the intrinsic linear contribution to the high-field MR does not depend on the crystalline quality of the films and supports the suggested intrinsic doubleexchange mechanism for CrO 2 .

Direct correlation of Cr 3 d orbital polarization and O K -edge X-ray magnetic circular dichroism of epitaxial CrO 2 films

“…Nearly no surface contamination of Cr 2 O 3 is present [14,15] which was also reported by other groups [16]. Further details of the sample growth and characterization have been discussed elsewhere [17].…”

Anomalous transport in half-metallic ferromagnetic CrO2

“…Growth on sapphire actually starts with Cr 2 O 3 and then changes to the required CrO 2 . 21,22 Grains are aligned at 60 • to each other with sixfold rotational symmetry of hexagonal crystal structure of underlying sapphire substrate. We earlier reported in some detail on the film growth, the morphology of the films, and also on the magnetization of the films.…”

Magnetic anisotropy of textured CrO 2 thin films investigated by X-ray magnetic circular dichroism

“…Characterization by X-ray diffractometry showed only CrO 2 (020) and (040) reflexes, indicating a preferred a-axis growth. Electron-diffraction analysis exhibits an artificial six-fold in-plane symmetry and a formation of twin boundaries [9]. A scanning electron microscopy (SEM) image of (010)-oriented CrO 2 crystallites on the Cr 2 O 3 (0001) initial layer is shown in Fig.…”