Quadrupolar Fluctuations in a Spin-1 Magnet

October 11, 2021
Quadrupolar Fluctuations in a Spin-1 Magnet
Hybridized quadrupolar and dipolar excitations in spin-1 FeI2. Left: The ground state of the ferromagnetic chain (bottom) has all spins in the Sz=+1 configuration. A single spin flip results in a spin with Sz=0 (top), an excitation with dipolar character. Two spin flips on the same site (middle) yield a bound excited state with quadrupolar character. Right: SU(3) theory shows the excitations are strongly hybridized and quantitatively explains the observed neutron scattering signal.

Scientific Achievement

It is shown that normally invisible quadrupolar spin fluctuations dominate the excitation spectrum of ordered FeI2.

Significance and Impact

The work shows how the effect of spin-orbit coupling can hybridize dipolar and quadrupolar fluctuations, leading to unexpected quantum excitations despite the classical ground-state, a result that may be applicable to a range of other materials with hitherto unexplained multipolar excitations.

Research Details

  • Successful comparison with SU(3) generalized spin-wave theory explained the observed neutron scattering and allowed extraction of most details of the complex magnetic Hamiltonian of FeI2.
  • Anisotropic exchange interactions are identified as the mechanism behind the dipolar-quadrupolar hybridization, solving a 40+ year old puzzle.

“Hybridized quadrupolar excitations in the spin-anisotropic frustrated magnet FeI2,”
Xiaojian Bai, Shang-Shun Zhang, Zhiling Dun, Hao Zhang, Qing Huang, Haidong Zhou, Matthew B. Stone, Alexander I. Kolesnikov, Feng Ye, Cristian D. Batista and Martin Mourigal,
Nature Physics 17, 467–472 (2021).
OI: https://doi.org/10.1038/s41567-020-01110-1