The Thermal Decomposition of Aqueous Chromic Acid and Some Properties of the Resulting Solid Phases<sup>1</sup>

Thamer, B.J.; Douglass, R.M.; Staritzky, Eugene.

doi:10.1021/ja01560a013

Cited by 60 publications

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“…The apical axis of the oxygen octahedra is oriented along the [110] ([110]) direction for the edge (bodycentered) Cr ions. The lattice parameters are a = b = 4.421 Å and c = 2.916 Å [6,7]. CrO 2 is a metastable Cr-oxide phase at room temperature, orders ferromagnetically at T C = 393 K and degrades above 400 K at ambient atmospheric pressures into the thermodynamically stable Cr 2 O 3 phase.…”

Section: Experiments and Resultsmentioning

confidence: 99%

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

Goering¹,

Justen²,

Geissler³

et al. 2002

Applied Physics A: Materials Science & Processing

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Highly a-axis-textured CrO 2 films have been deposited on Al 2 O 3 (0001) substrates by chemical vapor deposition. CrO 2 has been found to have highly a-axis (010)-oriented columnar growth on a Cr 2 O 3 (0001) initial layer. The sixfold surface symmetry of the Cr 2 O 3 initial layer leads to three equivalent in-plane orientations of the a-axis-oriented CrO 2 unit cell. We report Cr L 2,3 X-ray magnetic circular dichroism data along the surface normal and at 60 • off-normal sample orientation. For a 60 • sample alignment, a strong increase of the projected orbital moment could be observed for unoccupied majority t 2g states using moment analysis. Therefore, the c axis is identified as the intrinsic magnetic easy axis of CrO 2 . In addition, a small spin moment and a very strong magnetic dipole term T z have been found. PACS 75.30.Cr; 75.30.Gw; 78.20.Lj; 78.70.Dm; 78.20.Bk IntroductionThe theoretically predicted 100% spin polarization at the Fermi energy, ε F , of CrO 2 makes it a promising material for magnetoelectronic devices [1][2][3]. According to Jullière's model, the magnetoresistance (MR) of a ferromagnet/insulator/ferromagnet tunnel junction depends on the spin polarization of the electrode material used [4]. The MR increases with increasing spin polarization of the ferromagnetic electrode material. Also, injection of spins from ferromagnetic metals into semiconductors may be allowed only for highly polarized metallic electrodes [5]. Additionally, transition-metal oxides like CrO 2 , high-temperature superconductors and colossal magnetoresistance lanthanum-based manganates have attracted a lot of theoretical interest due to the complex interplay between orbital, structural and electronic degrees of freedom. This has revived research on half-metallic ferromagnetic transitionmetal oxides, especially CrO 2 , in the past few years. Unfortunately, CrO 2 is metastable at room temperature and atmospheric conditions and typically a thin Cr 2 O 3 layer covers the CrO 2 surface. Methods like photoemission (PES), ✉ Fax: +49-711/689-1912, E-mail: goering@mf.mpg.de X-ray absorption (XAS) or X-ray magnetic circular dichroism (XMCD) spectroscopy could not easily be used for examination of basic properties of CrO 2 , because of their intrinsic surface sensitivity. Therefore, only a few experimental results on single crystals or epitaxial-grown thin films have been published. Nevertheless, spectroscopic methods are able to give quantitative information about intrinsic magnetic properties of CrO 2 . Experiment and resultsCrO 2 crystallizes in a tetragonal rutile-type structure, where chromium atoms form a body-centered tetragonal unit cell. Cr sites are octahedrally surrounded by oxygen atoms. The apical axis of the oxygen octahedra is oriented along the [110] ([110]) direction for the edge (bodycentered) Cr ions. The lattice parameters are a = b = 4.421 Å and c = 2.916 Å [6,7]. CrO 2 is a metastable Cr-oxide phase at room temperature, orders ferromagnetically at T C = 393 K and degrades above 400 K at ambient atm...

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Section: Experiments and Resultsmentioning

confidence: 99%

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

Goering¹,

Justen²,

Geissler³

et al. 2002

Applied Physics A: Materials Science & Processing

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“…The Cr sites are octahedrally surrounded by oxygen atoms. The lattice parameters of the unit cell are a = 4.421 Å and c = 2.916 Å [13]. The CrO 2 phase is a metastable oxide phase that degrades at temperatures above 400 K and atmospheric pressure into the thermodynamically more stable Cr 2 O 3 phase (a = 4.951 Å; c = 13.566 Å; space group: R3c) [14].…”

Section: General Propertiesmentioning

confidence: 99%

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Rabe

Pommer

Samm

et al. 2001

J. Phys.: Condens. Matter

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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 .

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“…thick; Cu Kc¢ radiation; Eastman Kodak Type A film for which density was calibrated as a function of exposure time. The complete powder pattern is given by Thamer et al (1957). of oxygen ions at the vertices of deformed octahedra, with one chromium(III) ion at the center of each octahedron.…”

Section: Description Of the Structure And Position Of The Hydrogenmentioning

confidence: 99%

“…Uninterpreted powder X-ray diffraetion patterns, differential thermal analyses, a measured density and an approximate refractive index have been reported (Simon, Fischer & Schmidt, 1930;Laubengayer & McCune, 1952;Sharer & Roy, 1954). In the present investigation drusy aggregates of crystals up to several tenths of a millimetre across were available, prepared by thermal decomposition of aqueous chromic acid at 300 and 325 ° C. at elevated pressure (Thamer, Douglass & Staritzky, 1957). Quantitative chemical analysis of a sample of this material contaminated with chromium dioxide (Cr02; eassiterite structure) gave by weight 61.0% chromium and, by the Penfield method, 9% water, to be compared with 61.18% and 10.60%, respectively, calculated for HCr09.…”

Section: Introductionmentioning

confidence: 99%

The crystal structure of HCrO₂

Douglass¹

1957

Acta Cryst

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A structure for ttCrO~, has been found in which one ehromium(III) ion lies in 1 (a) 0, 0, 0 and two oxygen ions in 2 (c) x, x, x; x, x, x of space group Rgrn. The single parameter x has been determined from powder data by triM-and-error to be 0.405±0"003, with a residual factor R of 0.06 for resolved reflections not seriously affected by preferred orientation. The structure consists of distorted (CrO6) -9 octahedra, each sharing six of its edges with six surrounding eoplanar octahedra to form continuous sheets in which the anions are close packed, lying parallel to the prominent {111 } cleavage. This and certain other MX 2 structures containing sheets of linked octahedra differ from one another essentially only in the manner of superposition of successive sheets. In this structure, the sheets are stacked so that oxygen ions of adjacent sheets are exactly superposed, hence the anions in the structure as a whole are only partly close packed. One hydrogen ion lies between each pair of superposed oxygen ions, this O-H-O distance being 2-55± 0.08 A, in accord with infra-red absorption data. Symmetry indicates symmetrical hydrogen bonds, and in this respect the HCrO 2 structure appears unique among known isoformular structures.

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The Thermal Decomposition of Aqueous Chromic Acid and Some Properties of the Resulting Solid Phases¹

Cited by 60 publications

References 0 publications

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

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

Growth and magnetotransport study of thin ferromagnetic CrO₂films

The crystal structure of HCrO₂

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The Thermal Decomposition of Aqueous Chromic Acid and Some Properties of the Resulting Solid Phases1

Cited by 60 publications

References 0 publications

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

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

Growth and magnetotransport study of thin ferromagnetic CrO2films

The crystal structure of HCrO2

Contact Info

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The Thermal Decomposition of Aqueous Chromic Acid and Some Properties of the Resulting Solid Phases¹

Growth and magnetotransport study of thin ferromagnetic CrO₂films

The crystal structure of HCrO₂