[Paper Review] Intriguing magnetism of the topological kagome magnet TbMn_6Sn_6

C. Mielke, Wenlong Ma+25 more|arXiv (Cornell University)|Jan 14, 2021

Topological Materials and Phenomena4 citations

TL;DR

This study investigates the magnetic and topological properties of the kagome lattice material TbMn₆Sn₆ using muon spin rotation (μSR), neutron diffraction, and electrical transport. It identifies a temperature-driven evolution from dynamic to static out-of-plane ferrimagnetic order below 20 K, which is essential for stabilizing topological electronic states. Remarkably, hydrostatic pressure of 2.1 GPa induces a fully static topological ferrimagnetic ground state, enabling tunable control over topological responses.

ABSTRACT

Magnetic topological phases of quantum matter are an emerging frontier in physics and material science. Along these lines, several kagome magnets have appeared as the most promising platforms. Here, we explore magnetic correlations in the transition-metal-based kagome magnet TbMn$_{6}$Sn$_{6}$ using muon spin rotation, combined with local field analysis and neutron diffraction. Our results show that the system exhibits an out-of-plane ferrimagnetic structure $P6/mm'm'$ (comprised by Tb and Mn moments) with slow magnetic fluctuations below $T_{ m C2}$~=~320~K. These fluctuations exhibit a slowing down below $T_{ m C1}^{*}$~${\simeq}$~120~K, and we see the formation of static patches with ideal out-of-plane order below $T_{ m C1}$~${\simeq}$~20~K which grow in a volume with decreasing temperature. The appearance of the static patches has a similar onset to the interesting phenomenon such as spin-polarized Dirac dispersion with a large Chern gap and topological edge states. We further show that the temperature evolution of the anomalous Hall conductivity (AHC) is strongly influenced by the low temperature magnetic crossover. Our presented experimental results show that the onset of the topological electronic properties tied to the Dirac band is promoted only by true static out-of-plane ferrimagnetic order in TbMn$_{6}$Sn$_{6}$ and is washed out by the slow magnetic fluctuations above $T_{ m C1}$~${\simeq}$~20~K. Remarkably, hydrostatic pressure of 2.1 GPa stabilises static out-of-plane topological ferrimagnetic ground state in the whole volume of the sample. Therefore the exciting perspective arises of a magnetic system in which the topological response can be controlled, and thus explored, over a wide range of parameters.

Motivation & Objective

• To understand the magnetic order and fluctuations in the topological kagome magnet TbMn₆Sn₆.
• To determine the role of magnetic order in stabilizing topological electronic states such as the Dirac band and Chern gap.
• To investigate how external pressure influences the magnetic and topological phases in this system.
• To correlate the onset of static magnetic order with the emergence of topological Hall effect and anomalous Hall conductivity.
• To resolve the magnetic structure and phase transitions using muon spin rotation and neutron diffraction.

Proposed method

• Employed muon spin rotation (μSR) to probe local magnetic fields and dynamic fluctuations down to 1.8 K.
• Conducted neutron powder diffraction (NPD) and single-crystal neutron diffraction to determine the magnetic structure and lattice parameters.
• Used field-dependent neutron diffraction to detect spin reorientation transitions under applied magnetic fields.
• Performed zero-field μSR measurements to assess the onset of long-range magnetic order and internal field distribution.
• Analyzed temperature-dependent anomalous Hall conductivity (AHC) to link electronic transport to magnetic order.
• Applied hydrostatic pressure (2.1 GPa) to tune the magnetic phase and stabilize a homogeneous static topological ferrimagnetic state.

Experimental results

Research questions

• RQ1 What is the nature of the magnetic ground state in TbMn₆Sn₆, and how does it evolve with temperature?
• RQ2 How do dynamic magnetic fluctuations above 20 K affect the emergence of topological electronic states?
• RQ3 What is the role of static out-of-plane ferrimagnetic order in stabilizing the topological Hall effect and Chern gap?
• RQ4 Can hydrostatic pressure be used to induce a fully static topological ferrimagnetic state in TbMn₆Sn₆?
• RQ5 How does the temperature evolution of anomalous Hall conductivity correlate with magnetic phase transitions?

Key findings

• TbMn₆Sn₆ exhibits a static out-of-plane ferrimagnetic structure with space group $P6/mm'm'$ below $T_{ m C1} acksimeq 20$ K.
• Below $T_{ m C2} = 320$ K, the system displays slow magnetic fluctuations that slow down below $T_{ m C1}^* acksimeq 120$ K.
• Static magnetic patches with ideal out-of-plane order grow in volume as temperature decreases below 20 K.
• The onset of topological electronic properties, including spin-polarized Dirac dispersion and a large Chern gap, coincides with the formation of static out-of-plane order.
• Anomalous Hall conductivity (AHC) is strongly influenced by the low-temperature magnetic crossover, indicating a direct link to magnetic order.
• Hydrostatic pressure of 2.1 GPa stabilizes a fully static, homogeneous out-of-plane topological ferrimagnetic ground state across the entire sample volume.