Heavy-impurity resonance, hybridization, and phonon spectral functions in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>Fe</mml:mtext><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>M</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mtext>Si</mml:mtext></mml:mrow><mml:mi> </mml:mi><mml:mo>(</mml:mo><mml:mi>M</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">Ir</mml:mi><mml:mo>,</mml:mo><mml:mi> </mml:mi><mml:mi m

Delaire, Olivier; Al-Qasir, I. I.; May, Andrew F.; Li, Chen W.; Sales, B. C.; Niedziela, Jennifer L.; Ma, Jisheng; Matsuda, M.; Abernathy, D. L.; Berlijn, Tom

doi:10.1103/physrevb.91.094307

Cited by 41 publications

(22 citation statements)

References 80 publications

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“…8. The important consequence is again a significantly increased DOS at E Fermi in the PM phase, which gives rise to the anomalous softening of the vibrational modes in the PM phase due to adiabatic electron-phonon coupling [40,[80][81][82][83]. These observations are consistent with earlier temperature-dependent measurements of the thermopower [84], which is sensitive to the features in the electronic DOS close to the Fermi energy.…”

Section: Dft Calculationssupporting

confidence: 82%

“…Thus, vibrational entropy can be seen as measure of the elastic properties of the lattice, since a vibrating ion can occupy more phase space if it moves in a softer potential. The mechanism of adiabatic electron-phonon coupling links the availability of states at the Fermi level to the vibrational properties of the system [80][81][82][83]. This has been identified as the source of the anomalous softening in the hydrogen-free system [40,43,56].…”

Section: Dft Calculationsmentioning

confidence: 99%

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Influence of hydrogenation on the vibrational density of states of magnetocaloric LaFe11.4Si1.6H1.6

et al. 2020

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We report on the impact of magnetoelastic coupling on the magnetocaloric properties of LaFe11.4Si1.6H1.6 in terms of the vibrational (phonon) density of states (VDOS), which we determined with 57 Fe nuclear resonant inelastic X-ray scattering (NRIXS) measurements and with density-functional-theory (DFT)-based first-principles calculations in the ferromagnetic (FM) lowtemperature and paramagnetic (PM) high-temperature phase. In experiments and calculations, we observe pronounced differences in the shape of the Fe-partial VDOS between non-hydrogenated and hydrogenated samples. This shows that hydrogen does not only shift the temperature of the first-order phase transition, but also affects the elastic response of the Fe-subsystem significantly. In turn, the anomalous redshift of the Fe VDOS, observed by going to the low-volume PM phase, survives hydrogenation. As a consequence, the change in the Fe specific vibrational entropy ∆S lat across the phase transition has the same sign as the magnetic and electronic contribution. DFT calculations show that the same mechanism, which is a consequence of the itinerant electron metamagnetism associated with the Fe subsystem, is effective in both the hydrogenated and the hydrogen-free compounds. Although reduced by 50 % as compared to the hydrogen-free system, the measured change ∆S lat of (3.2 ± 1.9) J kgK across the FM to PM transition contributes with ∼ 35 % significantly and cooperatively to the total isothermal entropy change ∆Siso. Hydrogenation is observed to induce an overall blueshift of the Fe-VDOS with respect to the H-free compound; this effect, together with the enhanced Debye temperature observed, is a fingerprint of the hardening of the Fe sublattice by hydrogen incorporation. In addition, the mean Debye velocity of sound of LaFe11.4Si1.6H1.6 was determined from the NRIXS and the DFT data. arXiv:1911.11087v1 [cond-mat.mtrl-sci]

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Section: Dft Calculationssupporting

confidence: 82%

Section: Dft Calculationsmentioning

confidence: 99%

Influence of hydrogenation on the vibrational density of states of magnetocaloric LaFe11.4Si1.6H1.6

et al. 2020

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“…2(a,b), in particular the break in intensity near = 13 meV, appears similar to an avoided crossing of local-mode vibrations, which is observed in the excitation spectrum of other inhomogeneous materials [32][33][34][35][36].…”

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confidence: 78%

Lattice vibrations boost demagnetization entropy in a shape-memory alloy

et al. 2015

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Magnetocaloric (MC) materials present an avenue for chemical-free, solid state refrigeration through cooling via adiabatic demagnetization. We have used inelastic neutron scattering to measure the lattice dynamics in the MC material Ni45Co5Mn36.6In13.4. Upon heating across the Curie Temperature (TC), the material exhibits an anomalous increase in phonon entropy of 0.22 ± 0.04 /atom, which is ten times larger than expected from conventional thermal expansion. This transition is accompanied by an abrupt softening of the transverse optic phonon. We present first-principle calculations showing a strong coupling between lattice distortions and magnetic excitations.PACS numbers: 78.70. Nx, 75.30.Sg, 65.40.gd, 63.20.kk The coupling between magnetism and lattice excitations has been a recent topic of interest due to its importance in several solid-state systems, such as influencing decoherence in quantum magnets [1] and inducing a spin-Peierls transition in CuGeO 3 [2,3] and ZnCr 2 O 4 [4]. Studies of magnetoelastic materials have focused on metamagnetic shape memory alloys (MMSMA), which are able to reversibly deform with strains of up to ~6% [5,6] via a structural first-order phase transition (FOPT) [7][8][9]. The FOPT allows the alloy to function as magnetocaloric (MC) material, in which an adiabatic change in magnetization of the MMSMA causes an increase in its entropy, thus lowering its temperature [9][10][11][12]. While the change in entropy can be quite large, the FOPT is often accompanied by thermal and/or magnetic hysteresis, which limits the material's long term cycling efficiency. In addition, materials requiring a magnetic field of more than 2 T to induce the FOPT are not feasible for use in any magnetic refrigerator using permanent magnets [13,14].The paramagnetic-to-ferromagnetic secondorder phase transition (SOPT) offers a means to extract heat from a magnetic material using weaker applied magnetic fields and without hysteresis. This SOPT is present in any magnetic material at its Curie temperature ( ), but the change in entropy is typically significantly less than across the FOPT.In this letter, we quantify the phonon entropy and the magnon-phonon coupling in Ni45Co5Mn50-xInx (x=13.4) near the austenite using neutron scattering [15]. When annealed at temperatures below 900K, this compound forms a Huesler L21 structure that is stable down to the martensitic transition temperature , with Mn atoms occupying the 4a positions, Mn1-x/25Inx/25 the 4b, and Ni0.9Co0.1 the 8c positions (Wyckoff notation) [16]. The composition of the crystal puts it at a morphotropic phase boundary; decreasing x from 13.4 to 13.3 leads to an increase in by ~100K [17]. Ab initio calculations of similar compounds point to magnetic frustration as a possible explanation of the morphotropic phase boundary [18][19][20][21]. The magnetic exchange integral for nearest-neighbors Mn-Mn in the 4a and 4b positions -i.e. aligned along [100] -is predicted to be a large negative value (antiferromagnetic). Such an interaction competes ...

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“…2E, we can understand that the softening originates from the increased effective mass felt by the symmetric mode because more PNRs couple to and move collectively with the TA phonon. A key point here is that the PNRs are smaller than a large share of the phonon wavelengths, and for this reason, they manifest in a way that is more akin to an impurity mode ( 43 ) than to a macroscopic domain.…”

Section: Discussionmentioning

confidence: 99%

Giant electromechanical coupling of relaxor ferroelectrics controlled by polar nanoregion vibrations

et al. 2016

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Heavy-impurity resonance, hybridization, and phonon spectral functions inFe1−xMxSi (M=Ir,

Cited by 41 publications

References 80 publications

Influence of hydrogenation on the vibrational density of states of magnetocaloric LaFe11.4Si1.6H1.6

Influence of hydrogenation on the vibrational density of states of magnetocaloric LaFe11.4Si1.6H1.6

Lattice vibrations boost demagnetization entropy in a shape-memory alloy

Giant electromechanical coupling of relaxor ferroelectrics controlled by polar nanoregion vibrations

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