Magnetic Excitation Spectrum of the Square Lattice S=1/2 Heisenberg Antiferromagnet K2V3O8

Abstract

We have explored the magnetic excitation spectrum of the S=1/2 square lattice Heisenberg antiferromagnet, K2V3O8 using both triple-axis and time-of-flight inelastic neutron scattering. The long-wavelength spin waves are consistent with the previously determined Hamiltonian for this material. A small energy gap of 72+/-9 micro-eV is observed at the antiferromagnetic zone center and the near-neighbor exchange constant is determined to be 1.08+/-0.03 meV. A finite ferromagnetic interplanar coupling is observed along the crystallographic c-axis with a magnitude of Jc=-0.0036+/-0.006 meV. However, upon approaching the zone boundary, the observed excitation spectrum deviates significantly from the expectation of linear spin wave theory resulting in split modes at the (pi/2,pi/2) zone boundary point. The effects of magnon-phonon interaction, orbital degrees of freedom, multimagnon scattering, and dilution/site randomness are considered in the context of the mode splitting. Unfortunately, no fully satisfactory explanation of this phenomenon is found and further theoretical and experimental work is needed.

15 pages, 13 figures, submitted to Physical Review B

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• Quantum effects in a weakly-frustrated S=1/2 two-dimensional Heisenberg antiferromagnet in an applied magnetic field
• Spectrum of short-wavelength magnons in two-dimensional quantum Heisenberg antiferromagnet on a square lattice: third order expansion in 1/S
• Magnetic properties of the S=1/2 quasi square lattice antiferromagnet CuF2(H2O)2(pyz) (pyz=pyrazine) investigated by neutron scattering
• Coupling of spin and lattice modes in the S=1/2 two-dimensional antiferromagnet K${}_2$V${}_3$O${}_8$ with magneto-dielectric couplings
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• Uncovering anisotropic magnetic phases via fast dimensionality analysis
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