Low-temperature heat transport of Nd2CuO4: Roles of Nd magnons and spin-structure transitions

Abstract

We report the magnetic-field dependence of thermal conductivity (κ) of an insulating cuprate Nd2CuO4 at very low temperatures down to 0.3 K. It is found that apart from the paramagnetic moments scattering on phonons, the Nd 3+ magnons can act as either heat carriers or phonon scatterers, which strongly depends on the long-range antiferromagnetic transition and the fieldinduced transitions of spin structure. In particular, the Nd 3+ magnons can effectively transport heat in the spin-flopped state of the Nd 3+ sublattice. However, both the magnon transport and the magnetic scattering are quenched at very high fields. The spin re-orientations under the in-plane field can be conjectured from the detailed field dependence of κ.

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

“…2 shows the ratios l/W for the two samples, where W is the averaged sample width. 36,41 It is clear that both ratios increase quickly at very low temperatures and are expected to approach 1 below 0.3 K. This estimation tells us that it is not likely that the magnetic excitations in DTO (for examples, magnetic monopoles) can make a sizable contribution to transporting heat, since the experimental κ is even smaller than the phonon term in a boundary scattering limit. It should be pointed out that the magnetic-monopole excitations were believed to be negligible at very low temperatures, because the energy barrier for flipping a spin or creating a pair of magnetic monopoles is about 4.4 K. 42 …”

“…Using the β value obtained from specific-heat measurements (not shown here), the phonon velocity can be calculated and then the mean free path is obtained from the κ. 36,41 The inset to Fig. 2 shows the ratios l/W for the two samples, where W is the averaged sample width.…”

“…The thermal conductivity at low temperatures down to 0.3 K was measured using a conventional steady-state technique. 33,34,36,37 In this work, we measured thermal conductivities along and perpendicular to the (111) plane, named as κ and κ ⊥ , by using two samples with sizes of 5.3 × 0.74 × 0.16 mm 3 and 3.1 × 0.71 × 0.15 mm 3 , respectively. Note that the heat currents have to be along the longest dimension, while the magnetic field is always perpendicular to the (111) plane and is along the shortest and the longest dimension for κ and κ ⊥ samples, respectively.…”

“…[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.…”