Spin Fluctuations and Concentration Magnetic Transitions in Chiral Helical Ferromagnets Fe1 – xCoxSi

Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.; Bessonov, S. A.

doi:10.1134/s1063783420010266

Cited by 5 publications

(5 citation statements)

References 15 publications

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“…A possible reason for this discrepancy might root in the failure of DFT to capture the effect of electronic correlations which can dramatically change the overall behavior of the system, as was recently demonstrated using dynamical mean-field theory [49]. On the other hand, since the difference in total energy for q DFT min and q exp min due to the twist is small, E(q DFT min , Ω) − E(q exp min , Ω) = 8µeV, we speculate that it can be overtaken by higher order magnetic interactions [35] or by quantum fluctuations [50] shifting q DFT min towards q exp min .…”

Section: Discussionsupporting

confidence: 54%

Micromagnetic description of twisted spin spirals in the B20 chiral magnet FeGe from first principles

Grytsiuk,

Blügel

2021

Preprint

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Using the model of classical Heisenberg exchange and Dzyaloshinskii-Moriya (DM) interaction we show that the ground state of B20 FeGe chiral magnet is superposition of twisted helical spin-density waves formed by different sublattices of the crystal. Such twisted spin-density waves propagate in the same direction but with different phases and different directions of the rotation axes. We derive an advanced micromagnetic expression describing the exchange and DM interaction for such magnetic structure. By employing first-principles calculations based on density functional theory and using our micromagnetic model we show that the magnitude of the spin-spiral twist in B20 FeGe is of the same order as global spiraling. While the energy difference between the ground state of twisted spirals and the FM state is in good agreement to the experimental results, for the spin spirals without twist it is smaller by factor three. In addition, we verify our results by employing spin dynamic simulations. This calls for new experiments exploring the ground state properties of B20 chiral magnets.

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Section: Discussionsupporting

confidence: 54%

Micromagnetic description of twisted spin spirals in the B20 chiral magnet FeGe from first principles

Grytsiuk,

Blügel

2021

Preprint

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“…Let us consider a strongly correlated electronic system of chiral ferromagnets Fe 1−x Co x Si with Hamiltonian taking into account the zone motion energy, intra-atomic Coulomb spin and charge correlations, differing in nodes occupied by Fe atoms on Co. At the same time we will keep in mind that use of spin-dependent energy spectrum from first-principles LSDA + U + SO, causes concentration dependences and values of local magnetizations Fe 1−x Co x Si, not matching with the experimental data [7]. Satisfactory agreement with the experiment is obtained at self-consistent calculation of local magnetization within fluctuation theory of zone magnetism, where the results of the first-principles LDA + U + SO are used only to model electronic structure [5].…”

Section: Modelmentioning

confidence: 97%

“…In particular, such transition in the narrow range of temperatures (T s − T c ) ≪ T c occurs in MnSi, where it is accompanied by sharp change of volume and occurrence of lambdalike anomaly of VCTE [4]. A transition extended by temperature related to change of mode-mode parameter sign change in Fe 1−x Co x Si [5], as a result of fluctuations of intra-atomic potentials of electronelectron repulsion in nodes occupied by iron and cobalt atoms [5], is implemented in a wider range of temperatures (T s − T c ) ∼ T c , and in the experiment instead of lambdaanomaly of negative VCTEs, a wide temperature minimum occurs [6].…”

Section: Introductionmentioning

confidence: 94%

“…q and Im ξ (γ) q with q = 0, |ξ (γ) q | with q = (q, ω 2n ) at ω 2n = 0, η 0 (5) and are related to magnetization by ratios…”

Section: Modelmentioning

confidence: 99%

“…Going to thermodynamic potentials, let us consider the known ratio between statistical sum and free energy (F = T ln Z − µN), we will consider the terms of saddlepoint for functional integrals (4) by variables (5). At the same time the free energy of the system of correlated electrons with the volume-dependent energy spectrum ε k (V ) will be supplemented by the term of sum related to elastic deformation P = −K V (Kisothermal compressibility).…”

Section: Free Energy At Constant Pressurementioning

confidence: 99%

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Magnetovolume effects and thermal expansion in chiral helical ferromagnets Fe-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-Si

.A.

Volkov

Nogovitsyna

et al. 2022

Physics of the Solid State

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Within the framework of the theory of band magnetism and the Heine model for the volume dependence of the electronic spectrum, an approach is being developed to study magneto-volume effects in chiral helical ferromagnets. Using Fe1-xCoxSi as an example, it was found that in the range of long-range order (at temperature T<Tc) the magnetovolume effect is determined by the amplitude of helicoidal spin spirals and leads to the experimentally observed negative volume thermal expansion coefficient. In the region of phase transitions of the first order (from Tc to Ts) prolonged in temperature, a new mechanism of the magnetovolume effect is established due to the spatial fluctuations of spin spirals arising due to the difference in the Hubbard potentials of iron and cobalt. It is shown that the considered volume effects lead not only to the experimentally observed negative volume thermal expansion coefficient (VCTE) in the chiral spin short-range order phase, but also to a noticeable increase in the transition temperature to the paramagnetic state (T>Ts). Keywords: helicoidal ferromagnetism, chirality, spin fluctuations, electronic and crystal structure, thermal expansion.

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Phase transitions induced by concentration and thermodynamic magnetic fluctuations in chiral ferromagnets Fe1-xCoxSi

et al. 2021

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Taking into account the results of LDA+U+SO-modeling of the electronic structure of Fe1-xCoxSi, temperature-prolonged magnetic phase transitions of the first order in strongly correlated alloys with a broken crystal structure of the B20 type are investigated. It is shown that such phase transitions are induced by concentration and thermodynamic fluctuations for compositions with 0.2<x<0.65 and are accompanied by a change in the sign of the mode-mode coupling parameter. In this case, an intermediate region appears between the long-range order phases and the paramagnetic phase, with the short-range spin order characterized by ferromagnetic and helicoidal spatial fluctuations. We have defined the intervals of external magnetic fields, at which skyrmion microstructures spatially limited by the crossover of helicoidal and ferromagnetic fluctuations appear in the considered region of the extended phase transition. The peculiarities of the temperature dependences of the magnetic susceptibility in an external magnetic field, characteristic of the appearance of skyrmions, are obtained.

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Spin Fluctuations and Concentration Magnetic Transitions in Chiral Helical Ferromagnets Fe1 – xCoxSi

Cited by 5 publications

References 15 publications

Micromagnetic description of twisted spin spirals in the B20 chiral magnet FeGe from first principles

Micromagnetic description of twisted spin spirals in the B20 chiral magnet FeGe from first principles

Magnetovolume effects and thermal expansion in chiral helical ferromagnets Fe-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-Si

Phase transitions induced by concentration and thermodynamic magnetic fluctuations in chiral ferromagnets Fe1-xCoxSi

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