Electronic structure of the chromium dioxide (001) surface

Leuken, H. van; Groot, de Robert

doi:10.1103/physrevb.51.7176

Cited by 64 publications

(38 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A similar pseudogap is suggested by band structure calculations. 5,4,[6][7][8][9][10] Another indication of the form of the DOS is provided by spin-polarized point contact spectroscopy measurements which find almost total spin polarization near E F . 11 The nearly complete spin polarization implies a gap in the minority spin DOS.…”

mentioning

confidence: 99%

“…'' 3,4 Following the original paper by Schwarz,5 numerous band structure calculations indicate that CrO 2 is a halfmetallic ferromagnet with completely spin-polarized spin-up electrons at E F and a wide gap in the spin-down density of states ͑DOS͒. 4,[6][7][8][9][10] Recently a 90% spin polarization at E F has been measured in CrO 2 using superconducting point contact spectroscopy. 11 Here we investigate the electronic structure and charge dynamics in CrO 2 by means of reflectance spectroscopy carried out over the frequency range from 500 GHz to near ultraviolet.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Charge dynamics in the half-metallic ferromagnetCrO2

et al. 1999

View full text Add to dashboard Cite

Infrared spectroscopy is used to investigate the electronic structure and charge carrier relaxation in crystalline films of CrO 2 which is the simplest of all half-metallic ferromagnets. Chromium dioxide is a bad metal at room temperature but it has a remarkably low residual resistivity (Ͻ5 ⍀ cm) despite the small spectral weight associated with free carrier absorption. The infrared measurements show that low residual resistivity is due to the collapse of the scattering rate at Ͻ2000 cm Ϫ1 . The blocking of the relaxation channels at low and T can be attributed to the unique electronic structure of a half-metallic ferromagnet. In contrast to other ferromagnetic oxides, the intraband spectral weight is constant below the Curie temperature. ͓S0163-1829͑99͒14929-4͔Chromium dioxide is one of few binary oxides that are ferromagnetic metals. Acicular powders have long been used in particulate media for magnetic recording, but key aspects of the electronic structure of CrO 2 remain unexplored. Its resistivity dc is unusual: the residual resistivity 0 can be as small 5 ⍀ cm, but above 80 K, dc becomes strongly temperature dependent and exceeds 1000 ⍀ cm above the Curie temperature T C ϭ390 K, 1,2 a value which is beyond the Ioffe-Regel limit. Hence, CrO 2 may be classified as a ''bad metal. '' 3,4 Following the original paper by Schwarz, 5 numerous band structure calculations indicate that CrO 2 is a halfmetallic ferromagnet with completely spin-polarized spin-up electrons at E F and a wide gap in the spin-down density of states ͑DOS͒. 4,6-10 Recently a 90% spin polarization at E F has been measured in CrO 2 using superconducting point contact spectroscopy. 11 Here we investigate the electronic structure and charge dynamics in CrO 2 by means of reflectance spectroscopy carried out over the frequency range from 500 GHz to near ultraviolet. Our experiments reveal an interband contribution to the complex conductivity that is in accordance with a band structure entailing a high degree of spin polarization of the electronic states at E F . A half-metallic density of states implies a temperature-and frequency-dependent intraband scattering rate. The strong suppression of the scattering rate that we observe as , T˜0 is consistent with this notion of a ͑partial͒ gap in the electronic DOS. We have also analyzed the temperature dependence of the electronic spectral weight (N e f f ). In contrast to other ferromagnetic oxides, such as the manganites, we find no variation of N e f f with temperature.We measured the near-normal incidence reflectance R( ) of crystalline films of CrO 2 grown on a TiO 2 ͓110͔ substrate. 2 Films with thickness Ͼ5 m were found to be completely opaque throughout the experimental frequency range 14-37 000 cm Ϫ1 ͑2 -4600 meV͒. Films were coated in situ with gold or aluminum in the optical cryostat and the spectrum of the metal-coated sample was used as a reference. 12 Experimental errors due to diffuse reflectance are minimized with this procedure, allowing reliable absolute values of R( ) to be obtained. ...

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

Charge dynamics in the half-metallic ferromagnetCrO2

et al. 1999

View full text Add to dashboard Cite

show abstract

“…It is studied in pressed powders of CrO 2 , where it arises from contacts between particles. Chromium dioxide is an ideal material for spin-polarized electron tunneling, as it is a half-metallic ferromagnet where complete spin polarization of the conduction electrons is maintained up to the surface [15]. There are two 3d electrons in spinsplit t 2g subbands, one localized and the other in a halffilled band [16].…”

mentioning

confidence: 99%

Magnetoresistance of Chromium Dioxide Powder Compacts

et al. 1998

View full text Add to dashboard Cite

Cold-pressed powders of the half-metallic ferromagnet CrO 2 are dielectric granular metals. Hysteretic magnetoresistance with maxima at the coercive field arises from interparticle contacts. Dilution with insulating antiferromagnetic Cr 2 O 3 powder reduces the conductivity by 3 orders of magnitude, but enhances the magnetoresistance ratio which reaches 50% at 5K. The negative magnetoresistance is due to tunneling between contiguous ferromagnetic particles along a critical path with a spin-dependent Coulomb gap. [S0031-9007(98)05996-1] PACS numbers: 72.15. Gd, 73.40.Gk, 75.50.Cc, 81.20.Ev Negative magnetoresistance has been widely investigated in ferromagnetic metals and heterostructures. Effects intrinsic to a material are distinguished from extrinsic effects which depend on the direction of magnetization in adjacent ferromagnetic regions. Examples of the former include the anisotropic magnetoresistance of permalloy [1] or the colossal magnetoresistance of nonstoichiometric EuO [2] and mixed-valence manganites [3]. Examples of the latter are the giant magnetoresistance of multilayers [4] and granular metals [5,6] or the behavior of spin-dependent tunnel junctions [7], where resistivity is greatest at the coercive or switching field and decreases as the sample reaches technical saturation. Recent experiments on epitaxial manganite films with a single grain boundary have allowed the high-field, colossal magnetoresistance to be separated from the low-field effect due to heterogeneous magnetization distribution in adjacent grains [8,9]. A characteristic but unexplained feature of the low-field magnetoresistance in manganite ceramics [10], polycrystalline films [11,12], and tunnel junctions [13,14] is its rapid decay with increasing temperature.Here we report a new type of extrinsic magnetoresistance. It is studied in pressed powders of CrO 2 , where it arises from contacts between particles. Chromium dioxide is an ideal material for spin-polarized electron tunneling, as it is a half-metallic ferromagnet where complete spin polarization of the conduction electrons is maintained up to the surface [15]. There are two 3d electrons in spinsplit t 2g subbands, one localized and the other in a halffilled band [16]. The two electrons are strongly coupled by the on-site exchange interaction J H ഠ 1 eV. The intrinsic metallic nature of the oxide is illustrated by the resistivity of an oriented film grown on TiO 2 , shown in Fig. 1(a). It follows Matthiessen's rule with a residual resistivity of 0.1 mV m ͑10 mV cm͒ and a room-temperature value about 30 times greater. The slope dr͞dT remains positive above the Curie temperature ͑T C 396 K͒ [17]. The films exhibit only a small linear intrinsic magnetoresistance effect, ͑1͞m 0 r͒dr͞dH ϳ1%͞T at room temperature.Our samples were made from a commercial CrO 2 powder used for magnetic recording. The powder is composed of acicular single-domain particles with an average length of 300 nm and an aspect ratio of about 8:1. Coercivity is 59 mT (590 G) at room temperature, rising up to ...

show abstract

“…CrO 2 has been attracting substantial theoretical [1][2][3][4][5][6][7] and experimental [8][9][10][11] interest in recent years, in part because of its practical importance in magnetic recording, and in part due to fundamental interest in its halfmetallic electronic structure and the implications of this. In half metals, one spin channel is metallic and the other is semiconducting.…”

mentioning

confidence: 99%

Transport, optical and electronic properties of the half metal CrO2

Mazin

Singh

Draxl

1999

Journal of Applied Physics

View full text Add to dashboard Cite

The half metal ferromagnet CrO2 has interesting and unusual electronic properties. As in many other cases when kinetic properties are not easily described by the conventional Bloch–Boltzmann theory, strong correlation effects of the Hubbard type were called for explanation of the electronic properties of CrO2. Here we report detailed analysis of the electronic structure and related properties of CrO2, based on state-of-the-art density functional calculations. We conclude that (1) the most current experimental data do not indicate an anomalously large mass renormalization, (2) temperature dependence of the resistivity is due mainly to the scattering by spin fluctuations, (3) coupling between charge (electrons) and spin (magnons) degrees of freedom is anomalously strong, (4) recent optical measurements can be reasonably interpreted within the quasi-one-electron density functional calculations, and (5) their deviation from the experiment is opposite to that expected in the Hubbard model, and agrees with a physical picture of electrons dressed by spin fluctuations.

show abstract

Electronic structure of the chromium dioxide (001) surface

Cited by 64 publications

References 11 publications

Charge dynamics in the half-metallic ferromagnetCrO2

Charge dynamics in the half-metallic ferromagnetCrO2

Magnetoresistance of Chromium Dioxide Powder Compacts

Transport, optical and electronic properties of the half metal CrO2

Contact Info

Product

Resources

About