Topics in One-Dimensional Magnetism

Abstract

<p>An experimental study of the dynamic properties of the quasi-one-dimensional magnetic materials CsMnBr₃ and CsMn₀.₈₉Fe₀.₁₁Br₃ has been carried out. In addition, some theoretical and computer simulation work was performed on aspects of the static behaviour of selected one-dimensional magnetic systems.</p> <p>CsMnBr₃ is a one-dimensional magnetic insulator. Its magnetic behaviour can be described by a Heisenberg antiferromagnetic chain system with weak easy plane anisotropy. A truly one-dimensional system cannot sustain long-range order at any non-zero temperature, although short-range correlations can be strong at low temperatures. We used neutron scattering techniques to examine both the delocalized (spin wave) and localized (soliton) excitations of CsMnBr₃ in its paramagnetic phase at low temperatures. Our results of the spin wave response compare favourably with recent theory of co-operative excitations in the absence of long-range order. Our measurements of the soliton response is in qualitative agreement with the relevant theory. Soliton-like spin configurations could also be directly observed in the results of a Monte Carlo simulation on a system representative of CsMnBr₃.</p> <p>We also used the Monte Carlo method to examine static spin correlation lengths within the XY to Heisenberg crossover temperature regime in CsMnBr₃.</p> <p>We measured the magnetic excitation spectrum of the magnetic impurity chain system CsMn₀.₈₉Fe₀.₁₁Br₃ at low temperatures by neutron scattering techniques. The response was qualitatively different from either CsMnBr₃ or previously studied magnetic vacancy chain systems and showed marked host mode-impurity mode interaction effects.</p> <p>Finally we utilized the computational ease afforded by one dimension to examine the strengths of biquadratic exchange interactions in selected Mn⁺² chain systems, including CsMnBr₃.</p>