Temperature dependence of phonons in 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Pd</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mi>Fe</mml:mi></mml:mrow></mml:math>
 through the Curie temperature

Yang, F. C.; Hellman, Olle; Lucas, M. S.; Smith, Harold L.; Saunders, Claire; Xiao, Yuming; Chow, Paul; Fultz, B.

doi:10.1103/physrevb.98.024301

Cited by 14 publications

(14 citation statements)

References 59 publications

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“…Early studies by Baltensperger and Helman 21 and Baltensperger 22 showed that the phonon frequencies of magnetic compounds depend on the spin order, and this type of interaction is still actively studied, mainly in the context of strongly correlated systems, in metallic oxides. Magnetism-dependent phonons were also found in relatively simple FM materials, such as body-centered cubic (bcc) Fe and Pd 3 Fe [23][24][25] . These FM materials exhibit phonon softening phenomena at elevated temperatures near T C , and several theoretical studies have revealed that this phonon softening is due to magnetic disordering [25][26][27][28][29][30][31][32] .…”

Section: Introductionmentioning

confidence: 96%

“…Magnetism-dependent phonons were also found in relatively simple FM materials, such as body-centered cubic (bcc) Fe and Pd 3 Fe [23][24][25] . These FM materials exhibit phonon softening phenomena at elevated temperatures near T C , and several theoretical studies have revealed that this phonon softening is due to magnetic disordering [25][26][27][28][29][30][31][32] . Regarding the predictive accuracy for T C , magnetism-dependent phonons, including the phonon softening, do not apparently seem to be related to T C .…”

Section: Introductionmentioning

confidence: 96%

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Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states

Tanaka

Gohda

2020

npj Comput Mater

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Prediction of the Curie temperature is of significant importance for the design of ferromagnetic materials. One of the most widely used methods to estimate the Curie temperature from first principles relies on a spin Hamiltonian, for example, the Heisenberg Hamiltonian, and exchange coupling parameters obtained by first-principles calculations at zero temperature. Even though there have been attempts to include the effects of magnetism on phonons, the influence of magnetism-dependent phonons on magnetism has been disregarded in the theoretical estimation of the Curie temperature. Here, we propose a first-principles thermodynamic approach to minimise the total free energy considering both the influences of magnetism on phonons and the feedback effect from phonons to magnetism. By applying our scheme to body-centered cubic Fe, we find a significant reduction of the Curie temperature due to the feedback effect. This result indicates the importance of the feedback effect for a quantitative description of finite-temperature magnetism. In addition, we point out that the reduction in the theoretical Curie temperature arises in a wide range of ferromagnetic materials that exhibit phonon softening due to magnetic disordering.

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Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 96%

Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states

Tanaka

Gohda

2020

npj Comput Mater

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“…These stochastically generated thermal displacements from Eqs. (2) and (3) sample the Born-Oppenheimer surface in the stochastically initialized temperature-dependent effective potential (s-TDEP) method [18][19][20]25,26]. This method approximates the inclusion of zero-point motion not included in AIMD simulations and connects seamlessly to the classical limit at high temperature.…”

Section: Introductionmentioning

confidence: 99%

“…This method approximates the inclusion of zero-point motion not included in AIMD simulations and connects seamlessly to the classical limit at high temperature. The s-TDEP procedure can be used to calculate force constants capturing anomalous high-temperature effects [25][26][27][28] to low-temperature quantum effects [29,30] at a much lower computational cost than what is required by AIMD. The force constants calculated with this method are numerically converged with respect to the number of configurations and supercell size.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of electron-phonon interactions in vanadium

2020

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First-principles calculations were used to study the Fermi surface of body-centered cubic vanadium at elevated temperatures. Supercell calculations accounted for effects of thermal atom displacements on band energies, and band unfolding was used to project the spectral weight of the electron states into the Brillouin zone of a standard bcc unit cell. An electronic topological transition (ETT, or Lifshitz transition) occurred near the point with increasing temperature, but the large thermal smearings from the atomic disorder and the Fermi-Dirac distribution reduced the effect of this ETT on the electron-phonon interactions. The phonon dispersions showed thermal stiffening of their Kohn anomalies near the point and of the longitudinal N phonon mode. In general the effects of the ETT were overcome by the thermal smearing of the Fermi surface that reduces the spanning vector densities for anomalous phonon modes.

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“…The other interaction is the effect of magnetic disordering on phonon frequencies. Some ferromagnetic materials such as bcc Fe and Pd 3 Fe shows phonon softening at elevated temperatures near T C [21][22][23] . Some research groups approached this phenomenon by different theoretical methods [23][24][25][26][27][28][29][30] and achieved the same conclusion: The phonon softening is due to magnetic disordering near T C .…”

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confidence: 99%

Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states

Tanaka,

Gohda

2020

Preprint

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Prediction of the Curie temperature is of significant importance for the design of ferromagnetic materials. Even though the Curie temperature has been estimated using the Heisenberg model, magnetic exchange coupling parameters widely used is thus far based on first-principles calculations at zero temperature. In the explicit consideration of temperature effects, it is important to minimise the total free energy, because the magnetic and phonon free energies correlate with each other. Here, we propose a first-principles thermodynamic approach to minimise the total free energy considering both the influences of magnetism on phonons and the feedback effect from phonons to magnetism. By applying our scheme to bcc Fe, we find a significant reduction of the Curie temperature due to the feedback effect. This result inevitably enforces us to change our convention as follows: we should use exchange coupling constants for the disordered local moment state, not for the ferromagnetic state, in the prediction of the Curie temperature. Our results not only change the fundamental understanding of finite-temperature magnetism but also provide a general framework to predict the Curie temperature more accurately.

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Temperature dependence of phonons in Pd3Fe through the Curie temperature

Cited by 14 publications

References 59 publications

Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states

Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states

Temperature dependence of electron-phonon interactions in vanadium

Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states

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