37 research outputs found
Analytical method to correct the neutron polarisation for triple-axis data
Polarised neutron scattering is the method of choice to study magnetism in
condensed matter. Polarised neutrons are yet typically very low in flux and
complex experimental configurations further reduce the count rate, neutron
polarisation corrections would therefore be needed. Here we analytically derive
formulae of the corrected partial differential scattering cross sections. The
analytical method is designed for the longitudinal polarisation analysis, and
the correction generally holds for time-independent polarised neutrons with a
triple-axis spectrometer. We then applied the correction to recent results of
our experiment on YFeO. Although there is a difficulty
with experimental determination of inefficiency parameters of neutron spin
polarisers and flippers, the correction appears to work properly.Comment: 6 pages, 2 figure
N\'eel-type skyrmion lattice in tetragonal polar magnet VOSeO
Formation of the triangular skyrmion-lattice is found in a tetragonal polar
magnet VOSeO. By magnetization and small-angle neutron scattering
measurements on the single crystals, we identify a cycloidal spin state at zero
field and a N\'eel-type skyrmion-lattice phase under a magnetic field along the
polar axis. Adjacent to this phase, another magnetic phase of an incommensurate
spin texture is identified at lower temperatures, tentatively assigned to a
square skyrmion-lattice phase. These findings exemplify the versatile features
of N\'eel-type skyrmions in bulk materials, and provide a unique occasion to
explore the physics of topological spin textures in polar magnets.Comment: 11 pages, 4 figures, supplemental material (7 pages
Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb_2Ti_2O_7
In a class of frustrated magnets known as spin ice, magnetic monopoles emerge
as classical defects and interact via the magnetic Coulomb law. With
quantum-mechanical interactions, these magnetic charges are carried by
fractionalised bosonic quasi-particles, spinons, which can undergo
Bose-Einstein condensation through a first-order transition via the Higgs
mechanism. Here, we report evidence of a Higgs transition from a magnetic
Coulomb liquid to a ferromagnet in single-crystal Yb2Ti2O7. Polarised
neutron-scattering experiments show that the diffuse [111]-rod scattering and
pinch-point features which develop on cooling are suddenly suppressed below T_C
~ 0.21 K, where magnetic Bragg peaks and a full depolarisation of the neutron
spins are observed with thermal hysteresis, indicating a first-order
ferromagnetic transition. Our results are explained on the basis of a quantum
spin-ice model, whose high-temperature phase is effectively described as a
magnetic Coulomb liquid, while the ground state shows a nearly collinear
ferromagnetism with gapped spin excitations.Comment: 36 pages, including 3 figures and supplement with 4 more figure