46 research outputs found
Establishing the fundamental magnetic interactions in the chiral skyrmionic Mott insulator Cu2OSeO3 by terahertz electron spin resonance
The recent discovery of skyrmions in CuOSeO has established a new
platform to create and manipulate skyrmionic spin textures. We use high-field
electron spin resonance (ESR) spectroscopy combining a terahertz free electron
laser and pulsed magnetic fields up to 64 T to probe and quantify its
microscopic spin-spin interactions. Besides providing direct access to the
long-wavelength Goldstone mode, this technique probes also the high-energy part
of the excitation spectrum which is inaccessible by standard low-frequency ESR.
Fitting the behavior of the observed modes in magnetic field to a theoretical
framework establishes experimentally that the fundamental magnetic building
blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled
tetrahedra.Comment: 5 pages, 3 Figure
Spin excitations in the skymion host Cu2OSeO3
We have used inelastic neutron scattering to measure the magnetic excitation
spectrum along the high-symmetry directions of the first Brillouin zone of the
magnetic skyrmion hosting compound CuOSeO. The majority of our
scattering data are consistent with the expectations of a recently proposed
model for the magnetic excitations in CuOSeO, and we report best-fit
parameters for the dominant exchange interactions. Important differences exist,
however, between our experimental findings and the model expectations. These
include the identification of two energy scales that likely arise due to
neglected anisotropic interactions. This feature of our work suggests that
anisotropy should be considered in future theoretical work aimed at the full
microscopic understanding of the emergence of the skyrmion state in this
material.Comment: 5 pages, 6 figure
Spin-stretching modes in anisotropic magnets: spin-wave excitations in the multiferroic Ba2CoGe2O7
We studied spin excitations of the multiferroic Ba2CoGe2O7 in high magnetic
fields up to 33 T. In the electron spin resonance and far infrared absorption
spectra we found several spin excitations beyond the two conventional magnon
modes expected for such a two-sublattice antiferromagnet. We show that a
multi-boson spin-wave theory can capture these unconventional modes, that
include spin-stretching modes associated with an oscillating magnetic dipole
(or only quadrupole) moment. The lack of the inversion symmetry allows these
modes to become electric dipole active. We expect that the spin-stretching
modes can be generally observed in inelastic neutron scattering and light
absorption experiments in a broad class of ordered S > 1/2 spin systems with
strong single-ion anisotropy and/or non-centrosymmetric lattice structure.Comment: 5+4 pages, 3 figures, supplement added, manuscript revise
In-situ electric field control of THz non-reciprocal directional dichroism in the multiferroic BaCoGeO
Non-reciprocal directional dichroism, also called the optical-diode effect,
is an appealing functional property inherent to the large class of
non-centrosymmetric magnets. However, the in-situ electric control of this
phenomenon is challenging as it requires a set of conditions to be fulfilled:
Special symmetries of the magnetic ground state, spin-excitations with
comparable magnetic- and electric-dipole activity and switchable electric
polarization. We demonstrate the isothermal electric switch between domains of
BaCoGeO possessing opposite magnetoelectric susceptibilities.
Combining THz spectroscopy and multiboson spin-wave analysis, we show that
unbalancing the population of antiferromagnetic domains generates the
non-reciprocal light absorption of spin excitations.Comment: version accepte
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Magnon spectrum of the helimagnetic insulator Cu2OSeO3
Complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understanding its abundant low-temperature magnetically ordered phases