Lattice dynamics and thermal transport in multiferroicCuCrO2

Abstract

Inelastic neutron and x-ray scattering measurements of phonons and spin waves were performed in the delafossite compound CuCrO2 over a wide range of temperature, and complemented with first-principles lattice dynamics simulations. The phonon dispersions and density of states are well reproduced by our density functional calculations, and reveal a strong anisotropy of Cu vibrations, which exhibit low-frequency modes of large amplitude parallel to the basal plane of the layered delafossite structure. The low frequency in-plane modes also show a systematic temperature dependence of neutron and x-ray scattering intensities. In addition, we find that spin fluctuations persist above 300 K, far above the Néel temperature for long-range antiferromagnetic order, T N ≃ 24 K. Our modeling of the thermal conductivity, based on our phonon measurements and simulations, reveals a significant anisotropy and indicates that spin fluctuations above T N constitute an important source of phonon scattering, considerably suppressing the thermal conductivity compared to that of the isostructural but non-magnetic compound CuAlO2.

Phonon dispersion of Mo-stabilized γ -U measured using inelastic x-ray scattering

“…The measured instrumental resolution function was convolved with a Lorentzian to describe the central elastic peak and a damped-harmonic-oscillator (DHO) function to describe the phonon peaks, as described elsewhere and included in the appendix. 15,16 Close to the zone center, the phonon peaks are readily discernible, but farther from the center, the peaks become challenging to distinguish from the background, likely reflecting some combination of the effects of quenched chemical disorder and the metastability of the cubic phase at room temperature. This is particularly apparent along the [100] and [111] directions, and manifests itself in particularly large linewidths, which are presented in the appendix.…”

“…where A is the amplitude, n(E) is the Bose-Einstein distribution function at energy transfer E, Γ is the full width at half max, E 0 is the phonon energy, and the ± is determined by E>0 (+) or E<0 (-). 15,16 The obtained linewidths are shown in figure 5 and all of the calculated phonon energies and linewidths are collected in table IV. Figure 6 shows the results of the BvK analysis for 4NN and 8NN.…”

Thermodynamic and Structural Properties of CuCrO2 and CuCr2O4: Experimental Investigation and Phase Equilibria Modeling of the Cu–Cr–O System

“…4−6 This phase also presents interest in thermoelectric applications, 7−9 catalytic/photocatalytic, 10−13 photocathode in dye-sensitized solar cells (DSSCs), 14−16 water splitting/H 2 production, 12,17 and multiferroic behavior. 18,19 Second, the copper chromite CuCr 2 O 4 presents a tetragonally distorted spinel structure (hausmannite type, space group I4 1 /amd; Figure 1b) at room temperature and transforms into a cubic structure (spinel type, space group Fd3̅ m; Figure 1c) through a transition involving the cooperative Jahn−Teller distortion at 580 ± 5 °C. 20,21 This spinel phase has wide commercial application as catalysts in organic synthesis process, 22−24 H 2 production, 25 and photovoltaic.…”

Spinons and damped phonons in spin-1/2 quantum-liquid Ba$_{4}$Ir${}_3$O${}_{10}$ observed by Raman scattering

“…But this type of phonon damping necessarily accompanies an unwanted consequence of reduced electrical conductivity. It is also established that spin-phonon coupling via magnetostriction can reduce the phonon lifetime, thus suppress phonon thermal conductivity [33]. Here we demonstrate that spin-orbit interaction, rather than magnetostriction, can be an efficient driver of phonon damping which extends possible thermoelectricity to a new class of materials: magnetically non-ordered 4d and 5d transition metal materials with strong spin-orbit interaction.…”