Orbital character of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">O</mml:mi><mml:mo>−</mml:mo><mml:mn>2</mml:mn><mml:mi>p</mml:mi></mml:math>unoccupied states near the Fermi level in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CrO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Stagarescu, Cristian; Su, Xinxin; East̀man, D. E.; Altmann, K. N.; Himpsel, F. J.; Gupta, AK

doi:10.1103/physrevb.61.r9233

Cited by 56 publications

(50 citation statements)

References 26 publications

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“…This picture is most consistent with the band-structure calculation of Korotin et al,7 in which states of O2p character are observed to extend to E F ; these states are in addition to those due to the narrow, hybridized pϪd bands. Recent x-ray-absorption spectra 31 and electron energy-loss spectra 32 have shown good agreement with this band-structure calculation.…”

Section: Discussionsupporting

confidence: 53%

Evidence for two-band magnetotransport in half-metallic chromium dioxide

et al. 2000

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Magnetotransport measurements were made on patterned, ͑110͒ oriented CrO 2 thin films grown by the high-pressure, thermal decomposition of CrO 3 onto rutile substrates. The low-temperature Hall effect exhibits a sign reversal from positive to negative as the magnetic field is increased above 1 T, which may be interpreted within a simple two-band model as indicating the presence of highly mobile ( h ϭ0.25 m 2 /V s) holes as well as a much larger number of less mobile electrons (nϭ0.4 electrons/Cr͒. Between 50 and 100 K, the field at which the sign reversal occurs rapidly increases and a contribution from the anomalous Hall effect becomes significant, while the large, positive transverse magnetoresistance ͑MR͒ observed at low temperatures changes over to a predominantly negative MR. These changes correlate with a thermally activated dependence in the resistivity of the form T 2 e Ϫ⌬/T with ⌬Ϸ80 K, reflecting the lack of temperature dependence in the resistivity at low temperatures and a T 2 behavior above 100 K. The high mobilities at low temperature which result in the observed positive MR reflect the suppression of spin-flip scattering expected for a half-metallic system. However, the changes in magnetotransport above the temperature ⌬ must be due to the onset of spin-flip scattering, even though k B ⌬ is much less than the expected energy gap in the minority spin density of states. The significance of ⌬ is discussed in terms of recent models for another half-metallic system, the perovskite manganites, and the possible formation of ''shadow bands.''

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Section: Discussionsupporting

confidence: 53%

Evidence for two-band magnetotransport in half-metallic chromium dioxide

et al. 2000

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“…From a simple sum-rule analysis, we get a decreased absolute projected orbital moment along the magnetic easy c-axis and a higher one along the hard a-axis, which is quite unexpected, because the easy axis for a nearly unstrained thin film is the c-axis [27,42]. This is in contradiction to Bruno's model for the intrinsic origin of magnetocrystalline easy-axis behavior with increased and nondecreased absolute orbital projections along the easy axis [43,44].…”

Section: Orbital Anisotropycontrasting

confidence: 49%

“…We have separated O K -edge spectra of CrO 2 into two different regions. First, 1 eV above threshold, which is unambiguously identified as unoccupied t 2g majority states and, second, a broader feature around 3 eV above, which corresponds to a mixture of t 2g e g minority and the e g majority states [27]. The latter represents band-structure-related values [1][2][3]26].…”

Section: 2mentioning

confidence: 99%

“…For a quantitative estimation of the Cr 2 O 3 spectral weight in our measurements we measured O K -edge spectra and fitted the normalized XAS data to digitized reference spectra for CrO 2 and Cr 2 O 3 [27]. This reference data has been slightly broadened to fit our experimental conditions.…”

Section: Cr 2 O 3 Contributionsmentioning

confidence: 99%

“…Assuming that this ratio stays constant for O K and Cr L 2,3 edges, we could estimate the nonmagnetic Cr 2 O 3 -related spectral weight in the nonmagnetic XAS resonance lines and calculate a correction factor of 1 + (1/1.3) = 1.8(−0.2/ + 0.3) for all magnetic moments, which have been extracted by sum-rule or moment analysis. The error bar has been calculated by quantitative estimation of the maximal Cr 2 O 3 contamination spectral weight in the CrO 2 reference spectra [27], which leads to an underestimation of Cr 2 O 3 . Using intensity relations from Nakajima et al [13] and an effective mean free path of 1.5 nm, we could obtain a maximal Cr 2 O 3 thickness of 0.4 nm, which is 0.6-nm smaller than the original tunneling-derived thickness value.…”

Section: Cr 2 O 3 Contributionsmentioning

confidence: 99%

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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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Synchrotron Radiation Techniques Based onX‐rayMagnetic Circular Dichroism

Schütz

Goering

Stoll

2007

Handbook of Magnetism and Advanced Magnetic Materials

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X‐ray magnetic circular dichroism (XMCD) results from the dependence of the absorption cross section on the magnetization of the target. The use of highly intense, circular‐polarized synchrotron X‐ray sources close to an absorption edge energy allows an element‐specific and quantitative determination of local magnetic spin and orbital moments. If the energy is tuned to the circular dichroic active absorption edges, most of the X‐ray spectroscopic scattering and imaging techniques can be extended to their magnetic counterpart, which provides new insights into magnetic, electronic, and geometric structures and phenomena.

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Orbital character ofO−2punoccupied states near the Fermi level inCrO2

Cited by 56 publications

References 26 publications

Evidence for two-band magnetotransport in half-metallic chromium dioxide

Evidence for two-band magnetotransport in half-metallic chromium dioxide

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

Synchrotron Radiation Techniques Based onX‐rayMagnetic Circular Dichroism

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