514 research outputs found
Exploring the origins of the Dzyalloshinski-Moria interaction in MnSi
By using magnetization and small-angle neutron scattering (SANS)
measurements, we have investigated the magnetic behavior of Mn_{1-x}Ir_{x}Si
system to explore the effect of increased carrier density and spin-orbit
interaction on the magnetic properties of MnSi. We determine estimates of the
spin wave stiffness and the Dzyalloshinski-Moria, DM, interaction strength and
compare with Mn_{1-x}Co_{x}Si and Mn_{1-x}Fe_{x}Si. Despite the large
differences in atomic mass and size of the substituted elements,
Mn_{1-x}Co_{x}Si and Mn_{1-x}Ir_{x}Si show nearly identical variations in their
magnetic properties with substitution. We find a systematic dependence of the
transition temperature, the ordered moment, the helix period and the DM
interaction strength with electron count for Mn{1-x}Ir{x}Si, Mn_{1-x}Co_{x}Si,
and Mn_{1-x}Fe_{x}Si indicating that the magnetic behavior is primarily
dependent upon the additional carrier density rather than on the mass or size
of the substituting species. This indicates that the variation in magnetic
properties, including the DM interaction strength, are primarily controlled by
the electronic structure as Co and Ir are isovalent. Our work suggests that
although the rigid band model of electronic structure along with Moira's model
of weak itinerant magnetism describe this system surprisingly well,
phenomenological models for the DM interaction strength are not adequate to
describe this system.Comment: 17 pages, 7 Figure
Pauli Paramagnetic Effects on Vortices in Superconducting TmNi2B2C
The magnetic field distribution around the vortices in TmNi2B2C in the
paramagnetic phase was studied experimentally as well as theoretically. The
vortex form factor, measured by small-angle neutron scattering, is found to be
field independent up to 0.6 Hc2 followed by a sharp decrease at higher fields.
The data are fitted well by solutions to the Eilenberger equations when
paramagnetic effects due to the exchange interaction with the localized 4f Tm
moments are included. The induced paramagnetic moments around the vortex cores
act to maintain the field contrast probed by the form factor.Comment: 4 pages, 4 figure
A Hybrid Lagrangian Variation Method for Bose-Einstein Condensates in Optical Lattices
Solving the Gross--Pitaevskii (GP) equation describing a Bose--Einstein
condensate (BEC) immersed in an optical lattice potential can be a numerically
demanding task. We present a variational technique for providing fast, accurate
solutions of the GP equation for systems where the external potential exhibits
rapid varation along one spatial direction. Examples of such systems include a
BEC subjected to a one--dimensional optical lattice or a Bragg pulse. This
variational method is a hybrid form of the Lagrangian Variational Method for
the GP equation in which a hybrid trial wavefunction assumes a gaussian form in
two coordinates while being totally unspecified in the third coordinate. The
resulting equations of motion consist of a quasi--one--dimensional GP equation
coupled to ordinary differential equations for the widths of the transverse
gaussians. We use this method to investigate how an optical lattice can be used
to move a condensate non--adiabatically.Comment: 16 pages and 1 figur
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