48 research outputs found
Local breaking of four-fold rotational symmetry by short-range magnetic order in heavily overdoped Ba(FeCu)As
We investigate Cu-doped Ba(FeCu)As with transport,
magnetic susceptibility, and elastic neutron scattering measurements. In the
heavily Cu-doped regime where long-range stripe-type antiferromagnetic order in
BaFeAs is suppressed, Ba(FeCu)As (0.145 0.553) samples exhibit spin-glass-like behavior in magnetic
susceptibility and insulating-like temperature dependence in electrical
transport. Using elastic neutron scattering, we find stripe-type short-range
magnetic order in the spin-glass region identified by susceptibility
measurements. The persistence of short-range magnetic order over a large doping
range in Ba(FeCu)As likely arises from local arrangements
of Fe and Cu that favor magnetic order, with Cu acting as vacancies relieving
magnetic frustration and degeneracy. These results indicate locally broken
four-fold rotational symmetry, suggesting that stripe-type magnetism is
ubiquitous in iron pnictides.Comment: accepted by Physical Review B Rapid Communication
Observation of a mesoscopic magnetic modulation in chiral Mn1/3NbS2
We have investigated the structural, magnetic, thermodynamic, and charge
transport properties of Mn1/3NbS2 single crystals through x-ray and neutron
diffraction, magnetization, specific heat, magnetoresistance, and Hall effect
measurements. Mn1/3NbS2 displays a magnetic transition at TC ~ 45 K with highly
anisotropic behavior expected for a hexagonal structured material. Below TC,
neutron diffraction reveals increased scattering near the structural Bragg
peaks having a wider Q-dependence along the c-axis than the nuclear Bragg
peaks. This indicates helimagnetism with a long pitch length of ~250 nm (or a
wavevector q~0.0025 {\AA}-1) along the c-axis. This q is substantially smaller
than that found for the helimagnetic state in isostructural Cr1/3NbS2 (0.015
{\AA}-1). Specific heat capacity measurements confirm a second-order magnetic
phase transition with a substantial magnetic contribution that persists to low
temperature. The large low-temperature specific heat capacity is consistent
with a large density of low-lying magnetic excitations that are likely
associated with topologically interesting magnetic modes. Changes to the
magnetoresistance, the magnetization, and the magnetic neutron diffraction,
which become more apparent below 20 K, imply a modification in the character of
the magnetic ordering corresponding to the magnetic contribution to the
specific heat capacity. These observations signify a more complex magnetic
structure both at zero and finite fields for Mn1/3NbS2 than for the
well-investigated Cr1/3NbS2.Comment: 22 pages, 7 figure
Magnetic order and fluctuations in quasi-two-dimensional planar magnet Sr(CoNi)As
We use neutron scattering to investigate spin excitations in
Sr(CoNiAs, which has a -axis incommensurate helical
structure of the two-dimensional (2D) in-plane ferromagnetic (FM) ordered
layers for . By comparing the wave vector and energy
dependent spin excitations in helical ordered
Sr(CoNi)As and paramagnetic SrCoAs, we find
that Ni-doping, while increasing lattice disorder in
Sr(CoNiAs, enhances quasi-2D FM spin fluctuations.
However, our band structure calculations within the combined density functional
theory and dynamic mean field theory (DFT+DMFT) failed to generate a correct
incommensurate wave vector for the observed helical order from nested Fermi
surfaces. Since transport measurements reveal increased in-plane and -axis
electrical resistivity with increasing Ni-doping and associated lattice
disorder, we conclude that the helical magnetic order in
Sr(CoNiAs may arise from a quantum order-by-disorder
mechanism through the itinerant electron mediated Ruderman-Kittel-Kasuya-Yosida
(RKKY) interactions