81 research outputs found
Magnetic Properties of a Two-Dimensional Mixed-Spin System
Using a Langmuir-Blodgett (LB) synthesis method, novel two-dimensional (2D)
mixed-spin magnetic systems, in which each magnetic layer is both structurally
and magnetically isolated, have been generated. Specifically, a 2D Fe-Ni
cyanide-bridged network with a face-centered square grid structure has been
magnetically and structurally characterized. The results indicate the presence
of ferromagnetic exchange interactions between the Fe () and
Ni (S=1) centers.Comment: 2 pages, 3 figs., submitted 23rd International Conference on Low
Temperature Physics (LT-23), Aug. 200
ESR Study of (C_5H_{12}N)_2CuBr_4
ESR studies at 9.27, 95.4, and 289.7 GHz have been performed on
(CHN)CuBr down to 3.7 K. The 9.27 GHz data were acquired
with a single crystal and do not indicate the presence of any structural
transitions. The high frequency data were collected with a polycrystalline
sample and resolved two absorbances, consistent with two crystallographic
orientations of the magnetic sites and with earlier ESR studies performed at
300 K. Below T, our data confirm the presence of a spin singlet
ground state.Comment: 2 pages, 4 figs., submitted 23rd International Conference on Low
Temperature Physics (LT-23), Aug. 200
Anisotropic photo-induced magnetism of a thin film
A magneto-optically active thin film of RbCo[Fe(CN)]
HO has been prepared using a sequential assembly method. Upon
irradiation with light and at 5 K, the net magnetization of the film increased
when the surface of the film was oriented parallel to the external magnetic
field of 0.1 T. However, when the surface of the film was perpendicular to the
field, the net magnetization \emph{decreased} upon irradiation. The presence of
dipolar fields and the low-dimensional nature of the system are used to
describe the orientation dependence of the photo-induced magnetization. The
ability to increase or decrease the photo-induced magnetization by changing the
orientation of the system with respect to the field is a new phenomenon that
may be useful in future device applications.Comment: 10 pages, 2 figures, 1 tabl
The Magnetic Spin Ladder (C_{5}H_{12}N)_{2}CuBr_{4}: High Field Magnetization and Scaling Near Quantum Criticality
The magnetization, T, 0.7 K K), from single
crystals and powder samples of (CHN)CuBr has been used
to identify this system as an Heisenberg two-leg ladder in the strong
coupling limit, K and K, with T and T. An inflection point in K) at
half-saturation, , is described by an effective \emph{XXZ} chain. The
data exhibit universal scaling behavior in the vicinity of and
, indicating the system is near a quantum critical point.Comment: 4 pages, 4 figure
Neutron scattering evidence for isolated spin-1/2 ladders in (CDN)CuBr
Inelastic neutron scattering was used to determine the spin Hamiltonian for
the singlet ground state system of fully deuterated BPCB,
(CDN)CuBr. A 2-leg spin-1/2 ladder model, with meV and meV, accurately describes
the data. The experimental limit on the effective inter-ladder exchange
constant is meV, and the limit on total
diagonal, intra-ladder exchange is meV. Including the
effects of copper to bromide covalent spin transfer on the magnetic
form-factor, the experimental ratios of intra-ladder bond energies are
consistent with the predictions of continuous unitary transformation.Comment: 10 pages, with 11 figure
Experimental Evidence of a Haldane Gap in an S = 2 Quasi-linear Chain Antiferromagnet
The magnetic susceptibility of the quasi-linear chain Heisenberg
antiferromagnet (2,-bipyridine)trichloromanganese(III), MnCl_{3}(bipy), has
been measured from 1.8 to 300 K with the magnetic field, H, parallel and
perpendicular to the chains. The analyzed data yield and K. The magnetization, M, has been studied at 30 mK and 1.4 K in H up to 16
T. No evidence of long-range order is observed. Depending on crystal
orientation, at 30 mK until a critical field is achieved ( and $H_{c\bot} = 1.8\pm 0.2 T), where M increases continuously
as H is increased. These results are interpreted as evidence of a Haldane gap.Comment: 11 pages, 4 figure
Neonatal Colonisation Expands a Specific Intestinal Antigen-Presenting Cell Subset Prior to CD4 T-Cell Expansion, without Altering T-Cell Repertoire
Interactions between the early-life colonising intestinal microbiota and the developing immune system are critical in determining the nature of immune responses in later life. Studies in neonatal animals in which this interaction can be examined are central to understanding the mechanisms by which the microbiota impacts on immune development and to developing therapies based on manipulation of the microbiome. The inbred piglet model represents a system that is comparable to human neonates and allows for control of the impact of maternal factors. Here we show that colonisation with a defined microbiota produces expansion of mucosal plasma cells and of T-lymphocytes without altering the repertoire of alpha beta T-cells in the intestine. Importantly, this is preceded by microbially-induced expansion of a signal regulatory protein α-positive (SIRPα+) antigen-presenting cell subset, whilst SIRPα−CD11R1+ antigen-presenting cells (APCs) are unaffected by colonisation. The central role of intestinal APCs in the induction and maintenance of mucosal immunity implicates SIRPα+ antigen-presenting cells as orchestrators of early-life mucosal immune development
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