Giant thermal magnetoconductivity inCrCl3and a general model for spin-phonon scattering

Abstract

Insulating quantum magnets lie at the forefront both of fundamental research into quantum matter and of technological exploitation in the increasingly applied field of spintronics. In this context, the magnetic thermal transport is a particularly sensitive probe of the elementary spin and exotic topological excitations in unconventional magnetic materials. However, magnetic contributions to heat conduction are invariably intertwined with lattice (phonon) contributions, and thus the issue of spin-phonon coupling in determining the spin and thermal transport properties of magnetic insulators becomes more important with every emergent topological magnetic system. Here we report the observation of an anomalously strong enhancement of the thermal conductivity, occurring at all relevant temperatures, in the layered honeycomb material CrCl3 in the presence of an applied magnetic field. Away from the magnetically ordered phase at low temperatures and small fields, there is no coherent spin contribution to the thermal conductivity, and hence the effect must be caused by a strong suppression of the phonon thermal conductivity due to magnetic fluctations, which are in turn suppressed by the field. We build an empirical model for the thermal conductivity of CrCl3 within a formalism assuming an independently determined number of spin-flip processes and an efficiency of the phonon scattering events they mediate. By extracting the intrinsic phonon thermal conductivity we obtain a quantitative description of our measured data at all fields and temperatures, and we demonstrate that the scattering efficiency is entirely independent of the applied field. In this way we use CrCl3 as a model system to understand the interactions between spin and phonon excitations in the context of thermal transport. We anticipate that the completely general framework we introduce will have broad implications for the interpretation of transport phenomena in magnetic quantum materials.

Hybrid topological magnon-phonon modes in honeycomb and kagome lattices

“…This work is partly motivated by recent observation of topological bosonic modes in several compounds such as Lu 2 V 2 O 7 23 , planar kagome magnets Cu(1,3benzenedicarboxylate) 24 and YMn 6 Sn 6 25 , Tb 3 Ga 5 O 12 11,32 , Tb 2 Ti 2 O 7 37 , and CrCl 3 47 as discussed in the introduction. The heat conduction supplemented to the system by a temperature gradiant however excites both magnons and phonons.…”

“…In our model systems, however, we couple the spin fluctuations to in-plane displacements through the DM interaction, which could be more relevant in two-dimensional and layered materials. The observation of giant thermal magnetoconductivity in the layered compound CrCl 3 , an insulating magnet with underlying honeycomb lattice, indicates that the phonons and their scattering from the magnons play an important role 47 . In cubic antiferromagnetic compound Cu 3 TeO 6 , whose magnon excitations are shown to be topological 48,49 , the inelastic neutron scattering provides compelling evidence of magnon-phonon coupling 50 .…”

Pivotal role of magnetic ordering and strain in lattice thermal conductivity of chromium-trihalide monolayers

“…For magnetically ordered CrCl 3 it was shown experimentally that at low temperature the in-plane lattice thermal conductivity (κ l ) strongly depends on the magnetic field, a phenomenon typically known as magneto-resistance [17]. This giant thermal magneto-resistance is due to the suppression of spin phonon scattering under magnetic field [17]. Similarly, it was predicted that CrI 3 exhibits giant spin-lattice coupling and exhibits different lattice thermal conductivity in PM and ferromagnetic FM phases [19].…”

“…Magnetic contributions to thermal transport are intertwined with phononic or lattice contribution and therefore the investigation of SPC is necessary to accurately determine thermal transport properties of magnetic materials. Some recent studies have explored SPC in CrX 3 (X= Cl, I) compounds [16][17][18] by stduing properties of paramagentic (PM), ferromagnetic (FM) and antiferromagnetic (AFM) phases. For magnetically ordered CrCl 3 it was shown experimentally that at low temperature the in-plane lattice thermal conductivity (κ l ) strongly depends on the magnetic field, a phenomenon typically known as magneto-resistance [17].…”

“…Some recent studies have explored SPC in CrX 3 (X= Cl, I) compounds [16][17][18] by stduing properties of paramagentic (PM), ferromagnetic (FM) and antiferromagnetic (AFM) phases. For magnetically ordered CrCl 3 it was shown experimentally that at low temperature the in-plane lattice thermal conductivity (κ l ) strongly depends on the magnetic field, a phenomenon typically known as magneto-resistance [17]. This giant thermal magneto-resistance is due to the suppression of spin phonon scattering under magnetic field [17].…”