Images of a first order spin-reorientation phase transition in a metallic kagome ferromagnet

TL;DR

This study demonstrates that the spin reorientation transition in the metallic kagome ferromagnet Fe3Sn2 is a first order phase transition with complex domain dynamics, affecting its electronic and magnetic properties.

Contribution

It provides direct imaging and thermodynamic evidence that the transition is first order, revealing nucleation, growth, and inhomogeneous electronic structures in Fe3Sn2.

Findings

Transition is first order with a critical end point.

Nucleation occurs at complex magnetic domain walls.

Inhomogeneous electronic structure influences conductivity.

Abstract

First order phase transitions, where one phase replaces another by virtue of a simple crossing of free energies, are best known between solids, liquids and vapours, but they also occur in a wide range of other contexts, including even elemental magnets. The key challenges are to establish whether a phase transition is indeed first order, and then to determine how the new phase emerges because this will determine thermodynamic and electronic properties. Here we meet both challenges for the spin reorientation transition in the topological metallic ferromagnet Fe3Sn2. Our magnetometry and variable temperature magnetic force microscopy experiments reveal that, analogous to the liquid-gas transition in the temperature-pressure plane, this transition is centred on a first order line terminating in a critical end point in the field-temperature plane. We directly image the nucleation and growth associated with the transition and show that the new phase emerges at the most convoluted magnetic domain walls for the high temperature phase and then moves to self organize at the domain centres of the high temperature phase. The dense domain patterns and phase coexistence imply a complex inhomogeneous electronic structure, which will yield anomalous contributions to the magnetic field- and temperature-dependent electrical conductivity.