One and two dimensional antiferromagnets

Low dimensional magnetic systems often exhibit fascinating and subtle effects that are the low dimension analogues of the magnetism observed in the high temperature superconductors.

One-dimensional Heisenberg antiferromagnets exhibit a rich variety of dynamics especially at low values of spin where quantum fluctuations become important. Quantum theories of the magnetic excitations in the spin=1/2 systems predict a broad continuum of intensity above the classical spin wave dispersion. Although systems with a spin of 5/2 and greater are known behave to classically, materials such as CsVCl3 which have S=3/2 inhabit a crossover region between these two regimes.

By aligning the one-dimensional axis of the crystal perpendicular to the incident wavevector it is possible to map the entire spin-wave dispersion in a single measurement. In a five day experiment on MARI the dispersion curve for CsVCl3 was measured. The dispersion curve itself closely resembles the classical models for spin-waves - however, the width of the excitations is much broader than expected, indicating that the spin-wave damping is much larger than would be expected from classical theories.

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