Magnetic soft modes in the locally distorted triangular antiferromagnet alpha-CaCr2O4

TL;DR

This study investigates the phase diagram and magnetic excitations of a distorted triangular antiferromagnet, alpha-CaCr2O4, revealing stable 120° spin structures and unusual roton-like minima through neutron scattering.

Contribution

It introduces a new type of two-dimensional distortion in triangular antiferromagnets and demonstrates its effects on magnetic order and excitations, especially in alpha-CaCr2O4.

Findings

Stable 120° spin structure over a wide exchange range

Discovery of roton-like minima in excitation spectrum

Proximity of alpha-CaCr2O4 to phase boundary

Abstract

In this paper we explore the phase diagram and excitations of a distorted triangular lattice antiferromagnet. The unique two-dimensional distortion considered here is very different from the 'isosceles'-type distortion that has been extensively investigated. We show that it is able to stabilize a 120{\deg} spin structure for a large range of exchange interaction values, while new structures are found for extreme distortions. A physical realization of this model is \alpha-CaCr2O4 which has 120{\deg} structure but lies very close to the phase boundary. This is verified by inelastic neutron scattering which reveals unusual roton-like minima at reciprocal space points different from those corresponding to the magnetic order.