Electronic Structure Changes across the Metamagnetic Transition in FeRh via Hard X-Ray Photoemission

Gray, A. X.; Cooke, David W.; Krüger, Péter; Bordel, C.; Kaiser, Alexander; Moyerman, S.; Fullerton, Eric E.; Ueda, Shigenori; Yamashita, Yoshiyuki; Gloskovskii, A.; Schneider, Claus M.; Drube, W.; Kobayashi, Keisuke; Hellman, F.; Fadley, C. S.

doi:10.1103/physrevlett.108.257208

Cited by 74 publications

(46 citation statements)

References 34 publications

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“…Keeping in mind the good agreement of the magnitude of S vib+el with the experimental entropy change, it is clear that the ground-state energy differences between B2(AF) and B2(FM) from our semilocal DFT calculations, grossly overestimate the T = 0 free energy difference between the two phases. This applies as well to the vast majority of DFT investigations although a recent comparison of the electronic density of states obtained from DFT calculations and HAXPES measurements [120] confirms a proper description of the electronic structure within the standard semilocal GGA used in our approach. 4 Also the early experiment of Ponomarev [57] yields a much smaller estimate for the Gibbs free energy difference at T = 0 of G exp (0) = 3.23 × 10 −10 J/kg = 5.38 meV/f.u.…”

Section: Thermodynamic Stability From Quasiharmonic Calculationssupporting

confidence: 74%

Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films

et al. 2016

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We present phonon dispersions, element-resolved vibrational density of states (VDOS) and corresponding thermodynamic properties obtained by a combination of density functional theory (DFT) and nuclear resonant inelastic x-ray scattering (NRIXS) across the metamagnetic transition of B2 FeRh in the bulk material and thin epitaxial films. We see distinct differences in the VDOS of the antiferromagnetic (AF) and ferromagnetic (FM) phases, which provide a microscopic proof of strong spin-phonon coupling in FeRh. The FM VDOS exhibits a particular sensitivity to the slight tetragonal distortions present in epitaxial films, which is not encountered in the AF phase. This results in a notable change in lattice entropy, which is important for the comparison between thin film and bulk results. Our calculations confirm the recently reported lattice instability in the AF phase. The imaginary frequencies at the X point depend critically on the Fe magnetic moment and atomic volume. Analyzing these nonvibrational modes leads to the discovery of a stable monoclinic ground-state structure, which is robustly predicted from DFT but not verified in our thin film experiments. Specific heat, entropy, and free energy calculated within the quasiharmonic approximation suggest that the new phase is possibly suppressed because of its relatively smaller lattice entropy. In the bulk phase, lattice vibrations contribute with the same sign and in similar magnitude to the isostructural AF-FM phase transition as excitations of the electronic and magnetic subsystems demonstrating that lattice degrees of freedom need to be included in thermodynamic modeling.

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Section: Thermodynamic Stability From Quasiharmonic Calculationssupporting

confidence: 74%

Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films

et al. 2016

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“…1,12,14 This technique enabled, e.g., calorimetry studies of epitaxial FeRh films. 15,16 Alternatively, a thick (10 nm) IBAD MgO with postdeposition annealing yielded promising results. 17 However, two fundamental challenges remain unresolved.…”

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confidence: 99%

Ultrathin IBAD MgO films for epitaxial growth on amorphous substrates and sub-50 nm membranes

Wang

Antonakos

Bordel

et al. 2016

Applied Physics Letters

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A fabrication process has been developed for high energy ion beam assisted deposition (IBAD) biaxial texturing of ultrathin (∼1 nm) MgO films, using a high ion-to-atom ratio and post-deposition annealing instead of a homoepitaxial MgO layer. These films serve as the seed layer for epitaxial growth of materials on amorphous substrates such as electron/X-ray transparent membranes or nanocalorimetry devices. Stress measurements and atomic force microscopy of the MgO films reveal decreased stress and surface roughness, while X-ray diffraction of epitaxial overlayers demonstrates the improved crystal quality of films grown epitaxially on IBAD MgO. The process simplifies the synthesis of IBAD MgO, fundamentally solves the “wrinkle” issue induced by the homoepitaxial layer on sub-50 nm membranes, and enables studies of epitaxial materials in electron/X-ray transmission and nanocalorimetry.

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“…First principles calculations show that there is also an underlying phase transition in the electronic structure, [23][24][25][26][27] a thesis for which there is growing experimental evidence. 11,[28][29][30] The magnetostructural phase transition is well-known to be of first order in this material, and as a result shows hysteresis and phase coexistence. The coexistence of the two phases has been inferred from transport measurements, 10 previous X-ray diffraction experiments, 22,31,32 X-ray magnetic circular dichroism spectroscopy, 33 and directly imaged using photoemission electron microscopy (PEEM).…”

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confidence: 99%

Asymmetric “melting” and “freezing” kinetics of the magnetostructural phase transition in B2-ordered FeRh epilayers

Vries

Loving

McLaren

et al. 2014

Applied Physics Letters

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Synchrotron X-ray diffraction was used to study the phase transformation processes during the magnetostructural transition in a B2-ordered FeRh (001)-oriented epilayer grown on MgO by sputtering. Out-of-plane lattice constant measurements within the hysteretic regime of the transition reveal a microstructure consistent with the coexistence of lattice-expanded and contracted phases in spatially distinct regions. It was found that the phase separation is more pronounced during cooling than heating. Furthermore, whilst lattice-expanded domains that span the height of the film can be undercooled by several kelvins, there is no equivalent superheating. This asymmetry between the cooling and heating processes in FeRh is consistent with the difference in the kinetics of generic freezing and melting transitions.

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Electronic Structure Changes across the Metamagnetic Transition in FeRh via Hard X-Ray Photoemission

Cited by 74 publications

References 34 publications

Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films

Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films

Ultrathin IBAD MgO films for epitaxial growth on amorphous substrates and sub-50 nm membranes

Asymmetric “melting” and “freezing” kinetics of the magnetostructural phase transition in B2-ordered FeRh epilayers

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