Easy-cone state mediating the spin reorientation in topological kagome magnet Fe$_3$Sn$_2$

TL;DR

This study uncovers a temperature-driven spin reorientation in Fe$_3$Sn$_2$, revealing an intermediate easy-cone magnetic state influenced by anisotropy interplay, supported by multiple experimental techniques and phenomenological analysis.

Contribution

It demonstrates the existence of an easy-cone spin state during the reorientation process in a kagome magnet, highlighting the role of anisotropy constants and magnetoelastic effects.

Findings

Identification of a crossover from easy-plane to easy-axis anisotropy.

Observation of an intermediate easy-cone magnetic state.

Detection of magnetoelastic effects during spin reorientation.

Abstract

We investigated temperature-driven spin reorientation (SR) in the itinerant kagome magnet Fe$_3$Sn$_2$ using high-resolution synchrotron x-ray diffraction, neutron diffraction, magnetometry, and magnetic force microscopy (MFM), further supported by phenomenological analysis. Our study reveals a crossover from the state with easy-plane anisotropy to the high-temperature state with uniaxial easy-axis anisotropy taking place between $\sim40-130$~ K through an intermediate easy-cone (or tilted spin) state. This state, induced by the interplay between the anisotropy constants $K_1$ and $K_2$, is clearly manifested in the thermal evolution of the magnetic structure factor, which reveals a gradual change of the SR angle $\mathbf{\theta}$ between $40-130$~K. We also found that the SR is accompanied by a magnetoelastic effect. Zero-field MFM images across the SR range show a transformation in surface magnetic patterns from a dendritic structure at 120~K, to domain wall dominated MFM contrast at 40~K.