Single to multiparticle excitations in the S=5/2 chiral magnet - MnSb₂O₆

Magnons, in classical systems, are well defined and long-lived transverse excitations of the localized ordered moment [1]. However, the single quasiparticle picture breaks down in low dimensional and low spin magnets [2] where neutron scattering experiments differ from predictions of harmonic spin-wave theory, displaying a momentum and energy broadened continuum of scattering. Noncollinear magnets are systems which may host a similar breakdown of harmonic spin waves. MnSb₂O₆ is a chiral magnet based upon localized S=5/2 moments with a Neel temperature of 12 K. We apply neutron spherical polarimetry and high resolution neutron inelastic scattering on single crystals to confirm the magnetic and nuclear structures, and to map out the low-energy spin fluctuations associated with the Neel ordered state. At higher energy transfers, a momentum and energy broadened continuum of scattering, which kinematically occurs at twice the energy of the low-energy harmonic spin-waves, is observed. MnSb₂O₆ therefore shows the breakdown of the single magnon picture in a high spin ordered chiral magnet.

[1] D. Pines, “Elementary Excitations in Solids” (W.A. Benjamin, 1963).
[2] T. Ohyama and H. Shiba, J. Phys. Soc. Jpn 62, 3277 (1993).