Neutron-scattering signature of the Dzyaloshinskii-Moriya interaction in nanoparticles
arxiv(2024)
摘要
The antisymmetric Dzyaloshinkii-Moriya interaction (DMI) arises in systems
with broken inversion symmetry and strong spin-orbit coupling. In conjunction
with the isotropic and symmetric exchange interaction, magnetic anisotropy, the
dipolar interaction, and an externally applied magnetic field, the DMI supports
and stabilizes the formation of various kinds of complex mesoscale
magnetization configurations, such as helices, spin spirals, skyrmions, or
hopfions. A question of importance in this context addresses the
neutron-scattering signature of the DMI, in particular in nanoparticle
assemblies, where the related magnetic scattering signal is diffuse in
character and not of the single-crystal diffraction-peak-type, as it is e.g.seen in the B20 compounds. Using micromagnetic simulations we study the effect
of the DMI in spherical FeGe nanoparticles on the randomly-averaged magnetic
neutron scattering observables, more specifically on the spin-flip small-angle
neutron scattering cross section, the related chiral function, and the
pair-distance distribution function. Within the studied parameter space for the
particle size (60 nm≤ L ≤ 200 nm) and the
applied magnetic field (-1 T≤μ_0 H_0 ≤ 1 T), we find that the chiral function is only nonzero when the DMI is
taken into account in the simulations. This result is discussed within the
context of the symmetry properties of the magnetization Fourier components and
of the involved energies under space inversion. Finally, for small applied
magnetic fields, we provide an easy-to-implement analytical correlation
function for the DMI-induced spin modulations (with wave vector
k_d). The corresponding randomly-averaged spin-flip SANS cross
section reproduces the main features found in the numerical simulations.
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