Magnon Thermal Conductivity Research Articles

Spin thermal conductivity of the Haldane chain compound [formula omitted

We report experimental results on the thermal conductivity of the spin S = 1 chain compound Y 2 BaNiO 5 in the temperature range between 5.5 and 300 K. The results show a clear anisotropic behavior of the thermal conductivity along different lattice directions. The contributions to the total thermal conductivity provided by phonons and magnons are estimated. The spin-related energy diffusion constant D E ( T ) , calculated from the experimental data of the magnon thermal conductivity, is approaching the theoretically predicted high-temperature limiting value close to room temperature. With decreasing temperature, D E ( T ) increases reaching a broad peak at about 120 K. At low temperatures, the scattering of spin excitations by magnetic impurities seems to be the major factor limiting the magnon thermal transport.

Magnon heat conductivity and mean free paths in two-leg spin ladders: A model-independent determination

The magnon thermal conductivity $\kappa_{\mathrm{mag}}$ of the spin ladders in $\rm Sr_{14}Cu_{24-x}Zn_xO_{41}$ has been investigated at low doping levels $x=0$, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic defects which define an upper limit for $l_{\mathrm{mag}}$ and therefore allow a clear-cut relation between $l_{\mathrm{mag}}$ and $\kappa_{\mathrm{mag}}$ to be established independently of any model. Over a large temperature range we observe a progressive suppression of $\kappa_{\mathrm{mag}}$ with increasing Zn-content and find in particular that with respect to pure $\rm Sr_{14}Cu_{24}O_{41}$ $\kappa_{\mathrm{mag}}$ is strongly suppressed even in the case of tiny impurity densities where $l_{\mathrm{mag}}\lesssim 374$~{\AA}. This shows unambiguously that large $l_{\mathrm{mag}}\approx 3000$~{\AA} which have been reported for $\rm Sr_{14}Cu_{24}O_{41}$ and $\rm La_{5}Ca_9Cu_{24}O_{41}$ on basis of a kinetic model are in the correct order of magnitude.

Scattering processes and magnon thermal conductivity in [formula omitted

We analyse the temperature dependence of the 1D magnon heat transport in La5Ca9Cu24O41 which contains undoped two-leg spinladders. In particular, we discuss possible scattering mechanisms which become relevant at elevated temperatures and thereby reduce the magnon thermal conductivity. Within the framework of a kinetic model, we find that the temperature dependence of the magnon mean free path lmag is well described if scattering of magnons by non-dispersive optical phonons is assumed. The phonon gap Δ≈800K extracted from the analysis is in good quantitative agreement with the energy of the Cu–O bond stretching modes in the ladder planes.

Magnon-hole scattering and charge order in Sr14-xCaxCu24O41.

The magnon thermal conductivity kappa(mag) of the hole-doped spin ladders in Sr14-xCaxCu24O41 has been investigated at low doping levels x. The analysis of kappa(mag) reveals a strong doping and temperature dependence of the magnon mean free path l(mag), which is a local probe for the interaction of magnons with the doped holes in the ladders. In particular, this novel approach to studying charge degrees of freedom via spin excitations shows that charge ordering of the holes in the ladders leads to a freezing out of magnon-hole scattering processes.

Magnon thermal conductivity in the spin-gap state and the antiferromagnetically ordered state of low-dimensional copper oxides

We have looked for large thermal-conductivity due to magnons, κ magnon, in various kinds of low-dimensional quantum spin systems, such as the two-leg spin-ladder system Sr 14Cu 24O 41, the two-dimensional spin-dimer system SrCu 2(BO 3) 2, the four-leg spin-ladder system La 2Cu 2O 5, the two-dimensional spin system Cu 3B 2O 6 and the one-dimensional spin system Ca 2Y 2Cu 5O 10, using large-sized single-crystals grown by the TSFZ method. Large κ magnon has been found in the spin-gap state of Sr 14Cu 24O 41 whose bandwidth of the triplet excitation is large, owing to the enhancement of the mean free path of magnons. In gapless systems, it has been found that κ magnon increases with increasing magnon-velocity, which increases with increasing exchange-interaction between Cu 2+ spins and is larger in antiferromagnetic spin-correlation systems than in ferromagnetic spin-correlation systems. Therefore, it is concluded that essential factors of large κ magnon are a large bandwidth of the triplet excitation in a spin-gap system, a large exchange-interaction and antiferromagnetic spin-correlation rather than ferromagnetic spin-correlation.

Magnon heat transport in doped La2CuO4.

We present results of the thermal conductivity of La2CuO4 and La(1.8)Eu(0.2)CuO4 single crystals which represent model systems for the two-dimensional spin-1/2 Heisenberg antiferromagnet on a square lattice. We find large anisotropies of the thermal conductivity which are explained in terms of two-dimensional heat conduction by magnons within the CuO2 planes. Nonmagnetic Zn substituted for Cu gradually suppresses this magnon thermal conductivity kappa(mag). A semiclassical analysis of kappa(mag) is shown to yield a magnon mean free path which scales linearly with the reciprocal concentration of Zn ions.

Thermal conductivity of La 0.67(Ca xSr 1− x) 0.33MnO 3 ( x=0, 0.5, 1) and La 0.6Y 0.07Ca 0.33MnO 3 pellets between 10 and 300 K

Thermal conductivity ( λ) of nanocrystalline La 0.67(Ca x Sr 1− x ) 0.33MnO 3 ( x=0, 0.5, 1) and La 0.6Y 0.07Ca 0.33MnO 3 pellets prepared by a novel ‘pyrophoric’ method have been studied between the temperature range 10 and 300 K. Our data show that the magnitude of thermal conductivity is strongly influenced by the ion substitutions at La-site. The analysis of the thermal conductivity data indicates that the thermal transport is governed largely by phonons scattering in these systems and the electronic contribution is as small as 0.2–1% of total thermal conductivity ( λ total). At low temperatures (<90 K) 2D like lattice defects contribute to the phonon scattering dominantly and its strength increases with increasing Sr content and also with partial substitution of La by Y. Depending upon the composition of the samples, the magnon thermal conductivity contributes 2–15% of λ total close to T C. In the paramagnetic regime the unusual increase in λ total keeps signature of large dynamic lattice distortion.

Electron and Magnon Contributions to the Thermal Conductivity of YBa2Cu3Oy(6.1&lt;y≤6.9) at Low Temperatures

The thermal conductivity κ of sintered samples of YBa 2 Cu 3 O y has been measured below 4.2 K. In the region of y ≤6.4, phonon and magnon contributions to κ can be separated by considering the difference between their T -dependences. By considering the y -dependence of κ, we can also separate the electron thermal conductivity κ el from κ, although it has been found to have the same T -dependence (κ el ∝ T 2 ) as that of the phonon contribution κ ph . This T -dependence is consistent with the d -wave symmetry of the superconducting order parameter. The magnon thermal conductivity κ m exhibits a crossover of its T -dependence around the temperature characterized by the interbilayer exchange coupling between Cu spins, J ⊥ . Information on the y -dependence of the superconducting order parameter has been deduced from that of κ el .

Magnon thermal conductivity of solid 3He in the U2D2 antiferromagnetic phase.

We report the first measurement of magnon thermal conductivity in monodomain single crystals of 3 He in the U2D2 antiferromagnetic phase. The magnon mean free path λ was found first to rise rapidly upon cooling below T N and then more slowly at low temperatures, depending upon the sample. The temperature dependence is consistent with magnon umklapp scattering at high T, i.e., λ proportional to T −2 exp(Δ/k B T), with Δ/k B determined to be 5.8(±0.3) mK. The limiting low-temperature values of λ varied from 0.3 to 3 μm

Thermal conductivity and electrical resistivity of gadolinium as functions of pressure and temperature.

The electrical resistivity \ensuremath{\rho} and the thermal diffusivity a of gadolinium have been measured as functions of T in the range 45--400 K. The thermal conductivity \ensuremath{\lambda} has been calculated from a and experimental data for the specific-heat capacity, ${c}_{p}$. \ensuremath{\lambda} can be analyzed in terms of simple models for the lattice and electronic components above the Curie temperature ${T}_{C}$\ensuremath{\simeq}291.4 K. Below ${T}_{C}$ an additional term, identified as a magnon (spin-wave) thermal conductivity ${\ensuremath{\lambda}}_{m}$, is found. \ensuremath{\rho} and \ensuremath{\lambda} have also been studied as functions of T and P in the range 150--400 K and 0--2.5 GPa. The Lorenz function L=\ensuremath{\rho}\ensuremath{\lambda}/T increases by about 20%/GPa under pressure due to a very strong pressure dependence of the lattice thermal conductivity. The pressure coefficients of \ensuremath{\rho} and \ensuremath{\lambda} are -5.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}2}$ and 0.22 ${\mathrm{GPa}}^{\mathrm{\ensuremath{-}}1}$, respectively, at 300 K (above ${T}_{C}$), and 0 and 0.16 ${\mathrm{GPa}}^{\mathrm{\ensuremath{-}}1}$ at 200 K (below ${T}_{C}$). ${T}_{C}$ and the spin-reorganization temperature ${T}_{r}$\ensuremath{\simeq}219 K both decrease under pressure, at the rates -14.0 and -22.0 K/GPa, respectively. Although the magnitude of ${\ensuremath{\lambda}}_{m}$ cannot be accurately calculated from the zero-pressure data for \ensuremath{\lambda}, the temperature dependence of d\ensuremath{\lambda}/dP allows us to distinguish between several models and assign a value of ${\ensuremath{\lambda}}_{m}$\ensuremath{\simeq}1.5 W ${\mathrm{m}}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{K}}^{\mathrm{\ensuremath{-}}1}$, or 16.0% of \ensuremath{\lambda}, at 200 K.

The electronic Lorenz number and magnon thermal conductivity in nickel and its alloys at high temperatures

λ T versus T 2 plots of the thermal conductivity (λ) data on nickel and three NiRe alloys give electronic Lorenz numbers L e ∗ proportional to the electrical resistivity. The marked drop in L e ∗ below the Curie temperature is attributed to small-angle inelastic scattering of conduction electrons by magnons.

Low-temperature magnon thermal conductivity of ferromagnetic insulators with impurities

The spin-wave thermal conductivity at low temperatures has been calculated for ferromagnetic insulators containing magnetic defects. The temperature range is such that we neglect those magnon scattering processes which can redistribute the magnon distribution, such as the magnon-magnon interactions. The effect of the external magnetic field has also been studied, and we observe that within the validity of the energy relation $E(\stackrel{\ensuremath{\rightarrow}}{k})={\ensuremath{\alpha}k}^{2}$, the magnon conductivity has a ${T}^{2}$ dependence.

Effect of spin wave renormalization on magnon thermal conductivity

The spin wave renormalization, R, effectively modifies the temperature variation of the magnon thermal conductivity of magnetically ordered systems. This modification can explain the previous discrepancy between theoretical and experimental results.

Two-dimensional magnon and phonon thermal conductivity in high magnetic fields

Abstract The thermal conductivity of the two-dimensional Heisenberg ferromagnets (CnH2n+1NH3)2CuCl4, n = 1, 2 have been measured for temperatures between 1.5 and 25 K, and in fields up to 6.5 T. The heat current consists of a small phonon and a large (between 70 and 90%) magnon contribution, which is completely quenched for fields above 4.5 T.

Contribution to the theory of spin wave conductivity in non-metallic ferro- and ferrimagnets

The low temperature thermal properties of insulating ferro- and ferrimagnetic crystals containing an arbitrary concentration of randomly located magnon scattering centers are found for slab, cylindrical or prismatic samples. The magnon distribution function, energy density, and thermal conductivity are evaluated by analytically solving the non-linear Boltzmann equation. The scattering cross section is energy-dependent and anisotropic, and the magnon dispersion relation includes the effects of crystalline anisotropy, demagnetizing fields, and an external magnetic field. Theory and experiment are compared for yttrium iron garnet.

Electrical Resistivity, Thermal Conductivity and Magnetic Susceptibility of Polycrystalline Samarium at Low Temperatures

Electrical resistivity, thermal conductivity, and magnetic susceptibility have been measured, using the same sample of samarium, from 4 to 300 °K, from 5 to 200 °K, and from 4 to 300 °K, respectively. Two anomalies, one at 12 ± 1 °K and another at 106 ± 1 °K, are observed, resulting from an order-order magnetic transformation and an antiferromagnetic-paramagnetic transition, respectively. The Lorenz function is found to be larger at any temperature than that expected for pure electronic thermal conductivity. This implies that there is some phonon and possibly also some magnon thermal conductivity in samarium at low temperatures. The magnetic moment disorder electrical resistivity of samarium is determined to be 39.0 ± 0.5 μΩ cm, in fair agreement with the value to be expected from theoretical considerations.