Cr<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>—A New Half-Metallic Ferromagnet?

Kämper, K. P.; Schmitt, Walter; Güntherodt, G.; Gambino, R. J.; Ruf, R.

doi:10.1103/physrevlett.59.2788

Cited by 336 publications

(183 citation statements)

References 17 publications

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“…Together with the shift of the minority spin DOS from the bottom of the conduction band to higher energy, there appears a dip in the majority spin DOS at the Fermi level which can be taken as an indication of the tendency toward a gap formation. The decrease of the DOS at E F in comparison with that obtained in [8] may be partially responsible for the reduced signal close to E F observed in photo-electron spectroscopy [9]. In our calculations, however, CrO 2 is still a metal albeit with the reduced DOS at the Fermi level.…”

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confidence: 46%

“…However the magnetic susceptibility in the paramagnetic phase exhibits a Curie-Weiss-like behaviour with a local moment of also 2 µ B indicating that the mechanism for ferromagnetic behaviour is not a band (Stonerlike) mechanism. Local moments indicate strong correlation effects and this was in fact suggested by early photoemission data [9] which looked more like those of a semiconductor with a vanishing density of states (DOS) at the Fermi energy and a spin polarization of nearly 100 % for binding energies about 2 eV below the Fermi level. To resolve this controversy we carried out the calculations in the LSDA+U approach which is superior to LSDA since it can indeed yield a gap if the local Coulomb interactions are large enough.…”

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confidence: 99%

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CrO2: A Self-Doped Double Exchange Ferromagnet

et al. 1998

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Band structure calculations of CrO2 carried out in the LSDA+U approach reveal a clear picture of the physics behind the metallic ferromagnetic properties. Arguments are presented that the metallic ferromagnetic oxide CrO2 belongs to a class of materials in which magnetic ordering exists due to double exchange (in this respect CrO2 turns out to be similar to the CMR manganates). It is concluded that CrO2 has a small or even negative charge transfer gap which can result in self-doping. Certain experiments to check the proposed picture are suggested. 75.50.Ss, 75.30.Et There has been a revival in interest in 3d transition metal oxides during the last decade. This was initially stimulated by the discovery of High-T c superconductivity in complex copper oxides, and more recently by the active study of the colossal magnetoresistance manganates (CMR) La 1−x (Ca,Sr) x MnO 3 . These latter systems in the most interesting composition range are metallic ferromagnets. This is interesting in itself because ferromagnetic ordering is rare among the oxides: most of them are antiferromagnetic or ferrimagnetic with dominating antiferromagnetic interactions. We need to meet certain special conditions to stabilize ferromagnetism. One of the main mechanisms invoked to explain ferromagnetic ordering in these systems is the double exchange mechanism [1], although it is not the only one [2].Another very well known ferromagnetic and metallic compound is chromium dioxide CrO 2 widely used in magnetic recording tapes. In its formal 4+ valence state Cr has two 3d electrons in t 2g orbitals which in a simple picture of strong correlations would suggest a Mott insulating-like ground state with S=1 local moments and most likely antiferromagnetic spin order. This seems to be about as far from the actual observed properties as one can get. In this letter we will address this problem using band structure methods supplemented with local Coulomb and exchange interactions (LSDA+U, [3]) interpreted in terms of local electronic configurations. We will argue that the d electrons can be divided into a localized "core" of spin 1 2 and an itinerant d electron propagating through these "cores" resulting in a double exchangelike mechanism for the ferromagnetic order much as in the manganates. We also show that strong electron correlation effects do not in this case lead to an insulating ground state for reasonable values of the d-d Coulomb interaction and perfect stoichiometry because CrO 2 should be viewed as a small or even negative charge transfer gap [4] material in the Zaanen-Sawatzky-Allen (ZSA) scheme[5] quite unlike the parent CMR material LaMnO 3 which is a Mott-Hubbard insulator. This leads for CrO 2 quite naturally to a phenomenon which could be referred to as self-doping resulting in a non-integral 3d band occupa-CrO 2 is a ferromagnetic metal with a saturation magnetic moment of 2.00 µ B and a low temperature resistivity with a nearly T 2 temperature dependence [7]. Band structure calculations in LSDA [8] explain this behaviour as that of a...

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confidence: 99%

CrO2: A Self-Doped Double Exchange Ferromagnet

et al. 1998

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“…[14] Third, the present system has unique symmetry that ensures its topological character and is composed of two highly industrialized oxides, for which process technologies are rather mature for fabrication of the heterostructure. [20,21] In summary, we demonstrated that the interfacial electrons at the CrO 2 /TiO 2 heterojunction can be fashioned into single-spin Dirac states. In the superlattice model, we can obtain a Chern number = 2 QAH phase, which will enable dissipationless digital signal transmisstion with minimal influence of noise.…”

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confidence: 74%

“…Bulk CrO 2 (structure shown in Fig. 1) is a robust half metal even at elevated temperatures, [19][20][21] and widely used in enterprisegrade data storage. Here, we consider the possibility to fashion the CrO 2 into single-spin Dirac states by interfacial orbital design.…”

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Single-Spin Dirac Fermion and Chern Insulator Based on Simple Oxides

et al. 2015

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It is highly desirable to combine recent advances in the topological quantum phases with technologically relevant materials. Chromium dioxide (CrO2) is a half-metallic material, widely used in high-end data storage applications. Using first principles calculations, we show via interfacial orbital design that a novel class of half semi-metallic Dirac electronic phase emerges at the interface CrO2 with TiO2 in both thin film and superlattice configurations, with four spin-polarized Dirac points in momentum-space (k-space) band structure. When the spin and orbital degrees of freedom are allowed to couple, the CrO2/TiO2 superlattice becomes a Chern insulator without external fields or additional doping. With topological gaps equivalent to 43 Kelvin and a Chern number 2, the ensuing quantization of Hall conductance to 2e 2 /h will enable potential development of these highly industrialized oxides for applications in topologically high fidelity data storage and energy-efficient electronic and spintronic devices.The defining feature of massless Dirac Fermions [1,2] is the linear energy dispersion, implying that a quasiparticle moves at a constant speed independent of its energy, as governed by relativistic quantum mechanics. The exploration of novel Dirac materials with bulk Dirac or Dirac-Weyl states remains a great challenge in condensed matter and materials physics. [3][4][5][6][7][8][9][10] In particular, there has yet been neither theoretical proposal nor observation of materials systems with Dirac points a single spin species, which may be called a half-semimetal. Half metals are a class of ferromagnetic materials in which the conduction is dominated by one spin component while the other spin is gapped, which stands to enable reduced device size and non-volatile memory. At a rudimentary level, a half semi-metal will harbour the fascinating Dirac physics [1][2][3][4][5][6][7][8][9][10] all with a single spin. And as a not-so-trivial consequence, it may lead to Chern insulators [11][12][13][14] or valleytronics materials [15][16][17][18] when the low-energy excitations turn massive. In particular, a Chern insulator exhibits quantum anomalous Hall (QAH) effect in the absence of external magnetic field. This important fundamental phenomenon was established experimentally recently in magnetically doped topological insulator. [14] A spontaneous half semimetal will lead to a Chern insulator with appropriate spin-orbit coupling (SOC) and symmetry, which is advantageous for it requires no addition of impurity to the system. Precisely controlled growth of heterojunctions of oxides offers a unique avenue for exploring novel interfacial quantum phases, in which the interplay of orbital, charge, spin and lattice degrees of freedom gives rise to remarkably rich chemical, structural, electronic and magnetic varieties. Bulk CrO 2 (structure shown in Fig. 1) is a robust half metal even at elevated temperatures, [19][20][21] and widely used in enterprisegrade data storage. Here, we consider the possibility to fashion the CrO 2 int...

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“…The observed asymmetry implies the existence of spin-polarized currents, which are fully tunable by a proper choice of gate and bias voltages. By increasing the polarization of the ferromagnet, the diode effect could be increased up to a ∆I value of 100% [30]. Such carbon-nanotube spin diodes could easily be positioned using ac-dielectrophoresis [24], and could be operated at room temperature by reducing their size [31].…”

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confidence: 99%

Electrically Tunable Spin Polarization in a Carbon Nanotube Spin Diode

Merchant

Marković

2008

Phys. Rev. Lett.

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We have studied the current through a carbon nanotube quantum dot with one ferromagnetic and one normal-metal lead. For the values of gate voltage at which the normal lead is resonant with the single available non-degenerate energy level on the dot, we observe a pronounced decrease in the current for one bias direction.We show that this rectification is spin-dependent, and that it stems from the interplay between the spin accumulation and the Coulomb blockade on the quantum dot. Our results imply that the current is spin-polarized for one direction of the bias, and that the degree of spin polarization is fully and precisely tunable using the gate and bias voltages. As the operation of this spin diode does not require high magnetic fields or optics, it could be used as a building block for electrically controlled spintronic devices.The ability to create, manipulate and detect spin currents is central to the development of spintronic devices [1]. Controlling the spin currents by purely electrical means [2,3] is particularly interesting, as that would allow the integration of spintronic

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CrO2—A New Half-Metallic Ferromagnet?

Cited by 336 publications

References 17 publications

CrO2: A Self-Doped Double Exchange Ferromagnet

CrO2: A Self-Doped Double Exchange Ferromagnet

Single-Spin Dirac Fermion and Chern Insulator Based on Simple Oxides

Electrically Tunable Spin Polarization in a Carbon Nanotube Spin Diode

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