Abstract

I will discuss the properties of non-linear antiferromagnetic (AFM) chains, in which the orientation of the local environment of the magnetic ion is ‘staggered’, i.e. alternates in direction from site to site. Spin-1/2 non-linear chains exhibit additional terms in their Hamiltonians compared to linear chains, including non-trivial staggered g-tensors and Dzyalonshinskii-Moriya interactions. On application of an external magnetic field, these energy scales can give rise to staggered fields, field-dependent energy gaps and low-temperature excitation spectra containing both breather and soliton modes, observations that have previously been explained via the sine-Gordon model of quantum-field theory. Spin-1 AFM chains are known to adopt ground states that differ fundamentally from their spin-1/2 counterparts, an example being the topological Haldane-gapped phase, but until recently the effect of staggered local environments on spin-1 systems had not been explored.

Here, I present magnetometry, muon-spin rotation and neutron-scattering data on several new examples of non-linear spin chains. I will show that a chiral spin-1/2 chain with a four-fold periodic rotation of the local spin environment leads to properties distinct from the alternating chains previously studied. I will also discuss the results obtained by measuring non-linear spin-1 AFM chains, why these differ from the spin-1/2 materials and how competition between single-ion anisotropy and magnetic exchange can give rise to non-collinear or chiral magnetic ground-state structures.

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S. Vaidya et. al., Phys. Rev. B 110 , 174438 (2024)

S. Vaidya et. al., PRB 111 , 014421 (2025)