Pressure-induced phonon softenings and the structural and magnetic transitions in CrO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>

Kim, Sooran; Kim, Kyoo; Kang, Chang-Jong; Min, B. I.

doi:10.1103/physrevb.85.094106

Cited by 20 publications

(16 citation statements)

References 25 publications

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“…CrO 2 keeps NM up to 700 GPa considered in the present study. Our results do not support the FM-NM-FM transition proposed by Kim et al 26 Comparing previous investigations with our data, we are able to nd out that magnetism affects not only the structural stability of CrO 2 at high pressures but also other physical properties such as elasticity. [26][27][28] The DOS of various energetically favorable CrO 2 phases at high pressures calculated by the GGA + U method are plotted in Fig.…”

Section: Magnetic and Electronic Propertiescontrasting

confidence: 99%

“…The previous synchrotron X-ray diffraction (XRD) experiment and rst-principle simulations both conrmed a second-order structural transition of CrO 2 from rutile-type to CaCl 2 -type at $12 GPa. [24][25][26] Theoretical computations predicted a further transition to the CaF 2 -type structure at 89.6 GPa. 25 Recently, Wu et al 27 predicted a pressure-induced phase transition sequence of rutile-type / CaCl 2 -type / pyrite-type / CaF 2 -type for CrO 2 whereas calculated results by the GGA method demonstrated that CrO 2 underwent a transition sequence of rutile-type / CaCl 2 -type / PbO 2 -type / pyrite-type at high pressures.…”

Section: Introductionmentioning

confidence: 95%

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Structural, magnetic and electronic properties of CrO₂ at multimegabar pressures

Huang

Niu

et al. 2018

RSC Adv.

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Section: Magnetic and Electronic Propertiescontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Structural, magnetic and electronic properties of CrO₂ at multimegabar pressures

Huang

Niu

et al. 2018

RSC Adv.

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“…However, under high pressure the situation can change: the direct d-d hopping can begin to dominate, the bonding-antibonding splitting even in this 3D system can become comparable with what we have in 4d and 5d TM compounds at normal conditions, in which case our physics could come into play. Indeed, accurate band-structure calculations (36) have found a cascade of structural transitions in CrO 2 with pressure, with the formation of the dimerized monoclinic structure for P ∼ 70 GPa. As in the case of the Jahn-Teller distortions, it is not clear whether the lattice or electronic subsystem triggers the structural transition, but once the dimerization starts they go hand in hand and destabilize the DE state by lowering the energy of the xy molecular orbital.…”

Section: Suppression Of the Double Exchange And Magnetic Moment In Rementioning

confidence: 99%

Covalent bonds against magnetism in transition metal compounds

Streltsov

Khomskii

2016

Proc. Natl. Acad. Sci. U.S.A.

104

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Magnetism in transition metal compounds is usually considered starting from a description of isolated ions, as exact as possible, and treating their (exchange) interaction at a later stage. We show that this standard approach may break down in many cases, especially in 4d and 5d compounds. We argue that there is an important intersite effect-an orbital-selective formation of covalent metal-metal bonds that leads to an "exclusion" of corresponding electrons from the magnetic subsystem, and thus strongly affects magnetic properties of the system. This effect is especially prominent for noninteger electron number, when it results in suppression of the famous double exchange, the main mechanism of ferromagnetism in transition metal compounds. We study this mechanism analytically and numerically and show that it explains magnetic properties of not only several 4d-5d materials, including Nb 2 O 2 F 3 and Ba 5 AlIr 2 O 11 , but can also be operative in 3d transition metal oxides, e.g., in CrO 2 under pressure. We also discuss the role of spin-orbit coupling on the competition between covalency and magnetism. Our results demonstrate that strong intersite coupling may invalidate the standard single-site starting point for considering magnetism, and can lead to a qualitatively new behavior.double exchange | magnetism | transition metal compounds T ransition metal (TM) compounds present one of the main playgrounds in a large field of magnetism (1-3). Usually, when considering magnetic properties of these systems, one starts from the, as exact as possible, treatment of isolated TM ions or such ions in the surrounding of ligands, e.g., TMO 6 octahedra. A typical situation for a moderately strong crystal field is the one in which d electrons obey the Hund's rule, forming a state with the maximal spin. For a stronger crystal field low-spin states are also possible, but also in this case electrons in degenerate subshells, e.g., t 2g electrons, first form a state with maximal possible spin. Then, these large total spins interact by exchange coupling with the neighboring TM ions. This interaction, a superexchange for integer electron occupation (4), or a double exchange for partially filled d levels (5), is then treated using this starting point with this total spin of isolated ions, taking into account the hopping between sites (leading in effect to magnetic interaction) as a weak perturbation, which does not break the magnetic state of an ion.For heavier elements, such as 4d or 5d TM, one should also take into account the relativistic spin-orbit (SO) coupling, which couples the total spin S as dictated by the Hund's rule, with the (effective) orbital moment L. In any case, it is usually assumed that the "building blocks" for further consideration of the magnetic interactions are such isolated TM ions with the corresponding quantum numbers.However, especially when we go to heavier TM ions, such as 4d and 5d, also the spatial extent of the corresponding d orbitals increases strongly, and with it the effective d-d hopping, t (2). ...

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“…Therefore, investigation of physical properties of CrO 2 under high pressure and temperature has turned into an exceptionally important issue in recent years. The high pressure behaviour of CrO 2 has been extensively studied in a series of investigations [23][24][25][26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

Metal–insulator transition in the high pressure cubic $$\hbox {CaF}_{2}$$-type structure of $$\hbox {CrO}_{2}$$

Biswas¹

2018

Bull Mater Sci

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The total energy, magnetic moment, density of states and energy band structures of CrO 2 in the high pressure cubic CaF 2 (Fm-3m)-type structure are investigated for the first time by using first principles electronic structure calculations based on density functional theory in the local spin density approximation (LSDA) as well as using LSDA + U method. It is revealed from the present study that CrO 2 is a ferromagnetic nearly half-metal in the LDA calculation due to almost occupied Cr-3de g orbitals in the spin majority species and a tiny electron contribution at the Fermi level (E F) for spin minority species. This compound encounters metal-insulator transition (MIT) upon the application of Hubbard-type Coulomb repulsion U = 1 eV. Ferromagnetism is preserved in this transition. Application of U increases the electron correlation, which polarizes e g orbitals far below E F for spin majority channel while in the spin minority channel e g orbitals are polarized well above E F , resulting in opening of a band gap (E g ∼ 1.05 eV) in the vicinity of E F. Coulomb repulsion increases hybridization between occupied Cr-3de g and O-2p orbitals, which induces ferromagnetism both in half-metallic and insulating phases of cubic CrO 2 .

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Pressure-induced phonon softenings and the structural and magnetic transitions in CrO2

Cited by 20 publications

References 25 publications

Structural, magnetic and electronic properties of CrO₂ at multimegabar pressures

Structural, magnetic and electronic properties of CrO₂ at multimegabar pressures

Covalent bonds against magnetism in transition metal compounds

Metal–insulator transition in the high pressure cubic $$\hbox {CaF}_{2}$$-type structure of $$\hbox {CrO}_{2}$$

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Pressure-induced phonon softenings and the structural and magnetic transitions in CrO2

Cited by 20 publications

References 25 publications

Structural, magnetic and electronic properties of CrO2 at multimegabar pressures

Structural, magnetic and electronic properties of CrO2 at multimegabar pressures

Covalent bonds against magnetism in transition metal compounds

Metal–insulator transition in the high pressure cubic $$\hbox {CaF}_{2}$$-type structure of $$\hbox {CrO}_{2}$$

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Product

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Structural, magnetic and electronic properties of CrO₂ at multimegabar pressures

Structural, magnetic and electronic properties of CrO₂ at multimegabar pressures