Room-temperature observation of high-spin polarization of epitaxial CrO2(100) island films at the Fermi energy

Dedkov, Yuriy; Fonine, M.; König, Christian; Rüdiger, Ulrich; Güntherodt, G.; Senz, Stephan; Hesse, D.

doi:10.1063/1.1482142

Cited by 85 publications

(99 citation statements)

References 21 publications

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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: 76%

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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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confidence: 76%

“…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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confidence: 99%

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

et al. 2015

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“…There have been various arguments in favor of [27][28][29][30][31][32][33] and against 3,9,10,15-17 true half-metallic ferromagnetism. In our opinion, half-metallic ferromagnetism is an idealized limit, realistic only in perfect crystals at zero temperature.…”

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confidence: 99%

Finite-temperature spin polarization in half-metallic ferromagnets

Dowben

Skomski

2003

Journal of Applied Physics

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The temperature dependence of the spin polarization of half-metallic ferromagnets is investigated. A unitary spinor transformation shows that the corresponding spin mixing goes beyond finite-temperature smearing of the Fermi level, leading to a nonzero density of states in the gap of the insulating spin channel. As a consequence, the resistance ratio of the two spin channels changes from infinity to some finite value and, in a strict sense, half-metallic ferromagnetism is limited to zero temperature. Bloch-type spin waves and crystal imperfections contribute to the density of states in the gap but only partly explain the pronounced changes at about 0.2 T C observed in various half-metallic magnets. In the case of NiMnSb, the spin structure depends on a nearly dispersionless transverse optical mode that occurs at about 28 meV. In terms of 3 k B T, this corresponds to 103 K-very close to the temperature at which there is a dramatic loss in the Ni and Mn magnetization in NiMnSb. Similar modes exist in other potential half-metallic systems.

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“…Apart from a somewhat ambiguous scanning tunneling microscopy spectroscopy study undertaken at 77 K, 79 claims of 100% spin polarization at more elevated temperatures ͑Ͼ40 K͒ rest on evidence from spin-polarized photoemission [75][76][77] and spinpolarized inverse photoemission, 78 as summarized in Table I. Spin-resolved photoemission measurements [75][76][77] and spinpolarized inverse photoemission 78 that claim to provide evidence of half-metal behavior, in fact, do not. ͑Of course, not all such measurements of potential half-metallic systems have led to such claims.…”

Section: Experimental Proof Of Half-metallic Ferromagnetismmentioning

confidence: 99%

Are half-metallic ferromagnets half metals? (invited)

Dowben

Skomski

2004

Journal of Applied Physics

131

116

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Several classes of materials are currently under investigation as potential high-spin-polarization materials. Unfortunately, the proposed half-metallic materials, including the semi-Heusler alloys, the manganese perovskites, and the ''simpler'' oxides such as chromium dioxide and magnetite, suffer from fundamental limitations. First, the postulated half-metallic systems lose their full (T ϭ0) spin polarization at finite temperatures and, second, surfaces, interfaces, and structural inhomogenities destroy the complete spin polarization of half-metallic systems even at zero temperature. In a strict sense, half-metallic ferromagnetism is limited to zero temperature since magnon and phonon effects lead to reductions in polarization at finite temperatures.

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Room-temperature observation of high-spin polarization of epitaxial CrO2(100) island films at the Fermi energy

Cited by 85 publications

References 21 publications

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

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

Finite-temperature spin polarization in half-metallic ferromagnets

Are half-metallic ferromagnets half metals? (invited)

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