Single Ion Anisotropy of $Ln^{3+}$ (Ln = Tb, Dy, Ho) Controls Magnetic Excitations in $LnMn_{6}Sn_{6}$ Ferrimagnetic Kagome Metals

TL;DR

This study investigates how the magnetic anisotropy of lanthanide ions in $LnMn_{6}Sn_{6}$ ferrimagnetic kagome metals influences their magnetic excitations, revealing a pathway to tune magnon properties via lanthanide substitution.

Contribution

It provides the first detailed comparative analysis of magnetic dynamics in $LnMn_{6}Sn_{6}$ with different lanthanides, linking lanthanide anisotropy to magnon spectra.

Findings

Lanthanide identity affects magnon frequency.

Lanthanide anisotropy controls magnon properties.

Magnetic dynamics can be tuned by lanthanide substitution.

Abstract

The $LnMn_{6}Sn_{6}$ family of materials, where $Ln^{3+}$ is a lanthanide trivalent cation, have attracted extensive interest due to the interplay of electronic structure, magnetism, and topology present in this family that gives rise to complex electronic and magnetic phenomena. Specifically, the crystal field effects on the lanthanide ion and crystal field splitting of otherwise degenerate energy levels causes dramatic changes in the orbital magnetic behavior and overall magnetic structure of these materials. The coupling of the highly anisotropic lanthanide ions' spins (with large spin-orbit couplings) to the spins of the Mn atoms, which are arrayed in a kagome lattice, engenders exotic topological phenomena. This combination of magnetic anisotropy and electronic topology motivates investigation into the magnetic excitations of these materials, which unlike the ground state magnetic structures of this family, have not been extensively studied. Herein, we use Brillouin light scattering to measure the magnon spectra of $LnMn_{6}Sn_{6}$ (Ln = Tb, Dy, and Ho). This work represents the first detailed and comparative study on the magnetic dynamics in these materials and reveals that the identity of the lanthanide ion strongly influences the magnon frequency and demonstrates a direct correlation between the lanthanide's magnetic anisotropy and the observed spin wave excitations. Quantitative analysis indicates that the lanthanide ion's anisotropy controls the magnon frequency, while its total angular momentum influences the material's gyromagnetic ratio. These findings suggest that lanthanide substitution provides a pathway for tuning magnon properties in this material family.