Thermal conductivity of pure and Mg-dopedCuGeO3in the incommensurate phase

Abstract

The thermal conductivity κ of Cu1−xMgxGeO3 is measured in magnetic fields up to 16 T. At the transition field Hc to the high-field incommensurate (I) phase, κ abruptly decreases. While κ of the pure CuGeO3 is enhanced with the application of higher magnetic fields, an anomalous plateau feature shows up in the κ(H) profile in the I phase of the Mg-doped samples which includes antiferromagnetic ordering (I-AF phase). With the help of specific heat data, taken supplementally for the identical samples, the above features are well understood that phonons are strongly scattered by spin solitons and that κ in the I phase is governed by their spatial distribution. In particular, the plateau feature in the doped samples suggests "freezing" of the solitons, in which antiferromagnetism must be playing an essential role because this feature is absent at temperatures above TN .

Magnetothermal Transport in the Spin-12Chains of Copper Pyrazine Dinitrate

“…Experimental information on s B is, however, missing because most of the known realizations of the Hamiltonian (1) have large values of the intrachain exchange constant J=k B 100-1000 K, that severely limits the region of the phase diagram accessible using standard laboratory equipment. The existing results are limited to studies of the phonon thermal conductivity ph B; T in CuGeO 3 and Yb 4 As 3 [9][10][11][12], and do not address the behavior of s B; T. Copper pyrazine dinitrate CuC 4 H 4 N 2 NO 3 2 (CuPzN) appears to be an ideal compound for the thermal conductivity experiments in magnetic field, as J=k B 10:3 K [13,14] and therefore B c 15:0 T, which is easily accessible experimentally. CuPzN has an orthorhombic structure with lattice constants a 6:712 A, b 5:142 A, and c 11:73…”

Irreversible magnetic-field dependence of low-temperature heat transport of spin-ice compound Dy2Ti2O7in a

“…It is necessary to point out that the step-like decreases in the low-T κ(H) isotherms in some sense are not extraordinary, since similar anomalies have been observed in other magnetic materials 30,37 and are not difficult to understand. Although the hysteresis of κ(H) looks less remarkable than the step-like features in the magnitude, it is actually a more peculiar phenomenon related to the magnetism of the spin-ice materials.…”

“…Furthermore, some higher-field hysteresis of M (H) was observable only below 0.36 K. 16 Although the irreversibility of thermal conductivity can sometimes be observed at the field-induced first-order phase transitions in many materials, they are usually very small and presented in a narrow vicinity of the critical fields. 30 One exception for showing large hysteretic heat transport is the high-T c superconductors in the mixed state, 49 for which the hysteretic κ(H) behaviors are accompanied with the magnetization irreversibility caused by the vortex pinning. In other words, the difference of κ(H) between the field-up curve and the field-down one is directly related to the magnetism, which is reasonable because the density and distribution of the vortices determine the strength of vortex-electron scattering and the electron heat transport.…”

“…[30][31][32][33][34][35][36][37][38] However, the particular features of κ(H) at the magnetic transitions can be significantly different from each other, which depends on both the natures of magnetic transitions and the roles of magnetic excitations in the heat transport (as heat carriers or phonon scatterers). In principle, the magnetic monopoles as a kind of excitations in the spinice and kagomé-ice states can either transport heat or scatter phonons.…”

“…20,21 Studying spin-ice materials by using more different tech-niques is probably an effective way. Low-temperature heat transport is a powerful tool to probe the properties of elementary excitations [22][23][24][25][26][27][28][29] and the magnetic-field-induced magnetic transitions [30][31][32][33][34][35][36][37][38] . In principle, the magnetic monopoles, as the elementary excitations in the spin-ice compounds, can also contribute to the heat transport by acting as either heat carriers or phonon scatterers.…”