14 research outputs found
The Dielectric Response of La0.5Ca0.5-xSrxMnO3 (0.1 <= x <= 0.4) Manganites with Different Magnetic Ground States
The dielectric behavior of half doped manganites La0.5Ca0.5-xSrxMnO3 (0.1
\leq \times \leq 0.4) with varying magnetic ground states has been studied. The
real part of relative permittivity as a function of temperature
{\epsilon}^'(T), exhibits a maximum around the ferromagnetic (TC) and charge
ordering transition (TCO) temperatures accompanied with high dielectric losses.
The activation energies obtained for x = 0.1 and 0.3 samples below TCO are the
same ~ 0.12eV, whereas the relaxation time constant varies in the range 2.8
\times 10-9 s - 6.03 \times 10-11 s. In contrast to samples having x \leq 0.3,
for x = 0.4 doping the dielectric permittivity exhibits a strong temperature
dependence in the vicinity of magnetic phase transitions. This behavior may be
correlated with the presence of competing magnetic interactions (magnetic
polarons) close to the magnetic transitions.Comment: 14 pages, 5 figures, To appear in Journal of Applied Physic
A case of cerebral sinus venous thrombosis resulting in mortality in pregnant woman: late diagnosis
Cerebral venous sinus thrombosis (CVST) is a rare condition. The most frequent symptoms and signs are headache, focal seizures with or without secondary generalization, unilateral or bilateral paresis and papilledema. We report a case of CVST in a 30-yearold female that presented with headache, diminution of vision, swelling and pain in both eyes and bilateral restricted extraocular movements. She expired after 3 days of treatment as she was diagnosed late. Due to its diverse and varied clinical presentation, CVST should be considered as differential in almost any brain syndrome
Neutron tomography methods applied to a nickel-based superalloy additive manufacture build
Selective-laser melting (SLM) is one of the most rapidly developing and promising of all the so-called “Additive Manufacture” routes due to its capability to produce component geometries that would prove impossible using traditional manufacture. A selective-laser melting fabricated cuboid component was built using powder CM247LC, using standard methods, and this was subsequently analysed using neutron tomography methodology to allow for three-dimensional visualisation of the exterior and the interior of the component. The resulting neutron radiographs were processed and analysed for evidence of both porosity and grain boundary segregation within the component
Pressure effects on the magnetic structure in La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites
The effect of high pressure (0 - 8 GPa) on the magnetic structure of
polycrystalline samples of La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites at
5 K is investigated using neutron diffraction technique. Application of
pressure is found to modify the previously reported magnetic structure,
observed under ambient conditions, in these compounds [I. Dhiman et al., Phys.
Rev. B 77, 094440 (2008)]. In x = 0.1 composition, at 4.6(2) GPa and beyond,
A-type antiferromagnetic structure is found to coexist with CE-type
antiferromagnetic phase, observed at ambient pressure, with TN ~ 150 K. For x =
0.3 sample, as a function of pressure the CE-type phase is fully suppressed at
2.3(1) GPa and A-type antiferromagnetic phase is favored. Further Sr doping at
x = 0.4, the A-type antiferromagnetic phase is observed at ambient pressure and
for T < TN (~ 250K). This phase is retained in the studied pressure range.
However, the magnetic moment progressively reduces with increasing pressure,
indicating the suppression of A-type antiferromagnetic phase. The present study
brings out the fragile nature of the CE-type antiferromagnetic state in half
doped manganites as a function of pressure and disorder \sigma 2. We observe
that pressure required for destabilizing the CE-type antiferromagnetic state is
reduced with increasing disorder \sigma 2. External pressure and changing
A-site ionic radii have analogous effect on the magnetic structure.Comment: 9 pages, 6 figures, 1 table, To appear in Physical Review
Study of CeNi4Mn by neutron diffraction
We report neutron diffraction measurements on CeNi4Mn, which has recently
been identified as a soft ferromagnet (Tc ~ 140 K) with a sizeable
spin-transport polarization. Our data show conclusively that the Mn atoms
occupy a unique site (4c) in the unit cell, which has the symmetry of the cubic
MgCu4Sn-type structure. We infer a moment of 4.6 mu_B on Mn at 17 K, which is
oriented ferromagnetically along the {101} plane. The amplitude of the Mn
vibrational motion is found to be larger than that of Ce and Ni atoms at all
temperatures, thereby lending support to theoretical prediction of rattling
phonon modes in this compound.Comment: Accepted for publication in Solid State Commu
Neutron imaging and tomography with MCPs
A neutron imaging detector based on neutron-sensitive microchannel plates
(MCPs) was constructed and tested at beamlines of thermal and cold neutrons.
The MCPs are made of a glass mixture containing B-10 and natural Gd, which
makes the bulk of the MCP an efficient neutron converter. Contrary to the
neutron sensitive scintillator screens normally used in neutron imaging,
spatial resolution is not traded off with detection efficiency. While the best
neutron imaging scintillators have a detection efficiency around a percent, a
detection efficiency of around 50% for thermal neutrons and 70% for cold
neutrons has been demonstrated with these MCPs earlier.
Our tests show a performance similar to conventional neutron imaging
detectors, apart from the orders of magnitude better sensitivity. We
demonstrate a spatial resolution better than 150 um. The sensitivity of this
detector allows fast tomography and neutron video recording, and will make
smaller reactor sites and even portable sources suitable for neutron imaging.Comment: Submitted to the proceedings of the 19th International Workshop on
Radiation Imaging Detectors (iWoRiD) 2-6 July 2017, Krakow, Polan
Infrared absorption study of charge ordered
Infrared absorption study has been carried out on a series of half doped
manganites, , with
varying magnetic ground state. The charge ordering transition observed in
samples with {\normalsize is accompanied by a mode at
in addition to the stretching mode at and bending
mode at . Phonon hardening is found to occur below the CE - type
antiferromagnetic ordering temperature. The value of the insulating gap
decreases on doping with Sr from to }Comment: 14 pages, 5 figures, To appear in Physica
Influence of B - site Disorder in (B = Fe, Ru, Al and Ga) Manganites
We have investigated the influence of B - site doping on the crystal and
magnetic structure in (B= Fe, Ru, Al and
Ga) compounds using neutron diffraction, SANS, magnetization and resistivity
techniques. The B - site doped samples are isostructural and possess an
orthorhombic structure in \textit{Pnma} space group at 300K. A structural
transition from orthorhombic to monoclinic is found to precede the magnetic
transition to CE - type antiferromagnetic state in few of these samples. On
doping with Fe, charge and orbitally ordered CE - type antiferromagnetic state
is suppressed, followed by the growth in ferromagnetic insulating phase in
compounds. At higher Fe doping in , the
ferromagnetic state is also suppressed and no evidence of long range magnetic
ordering is observed. In Ru doped samples , the
ferromagnetic metallic state is favored at and
and no significant change in and as a
function of Ru doping is found. In contrast, with non magnetic Al substitution
for , the charge ordered CE - type antiferromagnetic state
coexists with the ferromagnetic metallic phase. With further increase in Al
doping , both CE - type antiferromagnetic and
ferromagnetic phases are gradually suppressed. This behavior is accompanied by
the evolution of A - type antiferromagnetic insulating state. Eventually, at
higher Al doping , this phase is also suppressed and
signature of spin glass like transition are evident in M(T). Likewise,
substitution with Ga is observed to induce similar effects as described for Al
doped samples. The presence of short ranged ferromagnetic ordering has been
further explored using SANS measurements in few of the selected samples.Comment: To appear in Journal of Physics: Condensed Matte