Domain imaging across the magneto-structural phase transition in Fe$_{1+y}$Te

TL;DR

This study uses spin-resolved scanning tunneling microscopy to explore how magnetic and structural phases evolve across the phase transition in Fe$_{1+y}$Te, revealing domain formation and phase coexistence related to excess Fe content.

Contribution

It provides the first real-space imaging of magnetic domain evolution and phase coexistence in Fe$_{1+y}$Te across the magnetic transition, highlighting the interplay of structure and magnetism.

Findings

Emergence of four magnetic domains in Fe$_{1.08}$Te during transition.

Disappearance of one domain boundary in Fe$_{1.12}$Te.

Broader transition into paramagnetic phase with phase mixture.

Abstract

The investigation of the magnetic phase transitions in the parent compounds of Fe-based superconductors is regarded essential for an understanding of the pairing mechanism in the related superconducting compounds. Even though the chemical and electronic properties of these materials are often strongly inhomogeneous on a nanometer length scale, studies of the magnetic phase transitions using spatially resolved experimental techniques are still scarce. Here, we present a real space spin-resolved scanning tunneling microscopy investigation of the surface of Fe$_{1+y}$Te single crystals with different excess Fe content, $y$, which are continuously driven through the magnetic phase transition. For Fe$_{1.08}$Te, the transition into the low-temperature monoclinic commensurate antiferromagnetic phase is accompanied by the sudden emergence of ordering into four rotational domains with different orientations of the monoclinic lattice and of the antiferromagnetic order, showing how structural and magnetic order are intertwined. In the low-temperature phase of Fe$_{1.12}$Te one type of the domain boundaries disappears, and the transition into the paramagnetic phase gets rather broad, which is assigned to the formation of a mixture of orthorhombic and monoclinic phases.