# Plaquette instability competing with bicollinear ground state in detwinned FeTe

## TL;DR

This study reveals that in FeTe, the bicollinear antiferromagnetic order is nearly degenerate with plaquette magnetic order, indicating strong magnetic frustration and complex spin dynamics in iron chalcogenides.

## Contribution

It demonstrates the coexistence and competition of bicollinear and plaquette magnetic orders in FeTe through neutron scattering, highlighting magnetic frustration in iron-based superconductors.

## Key findings

- Spin waves dissolve into isotropic scattering above 26 meV.
- Bicollinear order is quasidegenerate with plaquette order.
- Magnetic frustration is evidenced by competing magnetic states.

## Abstract

We use inelastic neutron scattering to show that long-range spin waves arising from the static bicollinear antiferromagnetic (AF) order in FeTe, which have twofold rotational symmetry in a fully detwinned crystal, rapidly dissolve above $E\approx 26$ meV into ridges of scattering with fourfold rotational symmetry and a nearly isotropic magnetic fluctuation spectrum. With increasing temperature above $T_N\approx 68$ K, the twofold spin waves change into broad regions of scattering with fourfold symmetry. Since the scattering patterns from plaquette magnetic order generated within a bilinear biquadratic Hamiltonian have fourfold rotational symmetry consistent with the high-energy, spin-isotropic spin waves of FeTe, we conclude that the bicollinear AF state in FeTe is quasidegenerate with plaquette magnetic order, providing evidence for the strongly frustrated nature of the local moments in iron chalcogenide family of iron-based superconductors.