299 research outputs found
Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSeS
We report muon spin rotation (SR) and magnetization measurements under
pressure on FeSeS with x
.Above GPa we find microscopic coexistence of
superconductivity with an extended dome of long range magnetic order that spans
a pressure range between previously reported separated magnetic phases. The
magnetism initially competes on an atomic scale with the coexisting
superconductivity leading to a local maximum and minimum of the superconducting
. The maximum of corresponds to the onset of
magnetism while the minimum coincides with the pressure of strongest
competition. A shift of the maximum of for a series of single
crystals with x up to 0.14 roughly extrapolates to a putative magnetic and
superconducting state at ambient pressure for x .Comment: 10 pages, 6 figures, including supplemental materia
Unconventional magnetism in the 4d based () honeycomb system AgLiRuO
We have investigated the thermodynamic and local magnetic properties of the
Mott insulating system AgLiRuO containing Ru
(4) for novel magnetism. The material crystallizes in a monoclinic
structure with RuO octahedra forming an edge-shared
two-dimensional honeycomb lattice with limited stacking order along the
-direction. The large negative Curie-Weiss temperature ( = -57
K) suggests antiferromagnetic interactions among Ru ions though magnetic
susceptibility and heat capacity show no indication of magnetic long-range
order down to 1.8 K and 0.4 K, respectively. Li nuclear magnetic
resonance (NMR) shift follows the bulk susceptibility between 120-300 K and
levels off below 120 K. Together with a power-law behavior in the temperature
dependent spin-lattice relaxation rate between 0.2 and 2 K, it suggest dynamic
spin correlations with gapless excitations. Electronic structure calculations
suggest an description of the Ru-moments and the possible importance of
further neighbour interactions as also bi-quadratic and ring-exchange terms in
determining the magnetic properties. Analysis of our SR data indicates
spin freezing below 5 K but the spins remain on the borderline between static
and dynamic magnetism even at 20 mK.Comment: 10 pages, 11 figures. accepted in Phys. Rev.
Towards understanding edge localised mode mitigation by resonant magnetic perturbations in MAST
Type-I Edge Localised Modes (ELMs) have been mitigated in MAST through the
application of n = 3, 4 and 6 resonant magnetic perturbations (RMPs). For each
toroidal mode number of the non-axisymmetric applied fields, the frequency of
the ELMs has been increased significantly, and the peak heat flux on the
divertor plates reduced commensurately. This increase in ELM frequency occurs
despite a significant drop in the edge pressure gradient, which would be
expected to stabilise the peeling-ballooning modes thought to be responsible
for type-I ELMs. Various mechanisms which could cause a destabilisation of the
peeling-ballooning modes are presented, including pedestal widening, plasma
rotation braking, three dimensional corrugation of the plasma boundary and the
existence of radially extended lobe structures near to the X-point. This leads
to a model aimed at resolving the apparent dichotomy of ELM control, that is to
say ELM suppression occurring due to the pedestal pressure reduction below the
peeling-ballooning stability boundary, whilst the reduction in pressure can
also lead to ELM mitigation, which is ostensibly a destabilisation of
peeling-ballooning modes. In the case of ELM mitigation, the pedestal
broadening, 3d corrugation or lobes near the X-point degrade ballooning
stability so much that the pedestal recovers rapidly to cross the new stability
boundary at lower pressure more frequently, whilst in the case of suppression,
the plasma parameters are such that the particle transport reduces the edge
pressure below the stability boundary which is only mildly affected by
negligible rotation braking, small edge corrugation or short, broad lobe
structures.Comment: 23 pages, 12 figures. Copyright (2013) United Kingdom Atomic Energy
Authority. This article may be downloaded for personal use only. Any other
use requires prior permission of the author and the American Institute of
Physic
Signature of a randomness-driven spin-liquid state in a frustrated magnet
Collective behaviour of electrons, frustration induced quantum fluctuations
and entanglement in quantum materials underlie some of the emergent quantum
phenomena with exotic quasi-particle excitations that are highly relevant for
technological applications. Herein, we present our thermodynamic and muon spin
relaxation measurements, complemented by ab initio density functional theory
and exact diagonalization results, on the recently synthesized frustrated
antiferromagnet Li4CuTeO6, in which Cu2+ ions (S = 1/2) constitute disordered
spin chains and ladders along the crystallographic [101] direction with weak
random inter-chain couplings. Our thermodynamic experiments detect neither
long-range magnetic ordering nor spin freezing down to 45 mK despite the
presence of strong antiferromagnetic interaction between Cu2+ moments leading
to a large effective Curie-Weiss temperature of -154 K. Muon spin relaxation
results are consistent with thermodynamic results. The temperature and magnetic
field scaling of magnetization and specific heat reveal a data collapse
pointing towards the presence of random-singlets within a disorder-driven
correlated and dynamic ground-state in this frustrated antiferromagnet
- …