171 research outputs found
Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys
A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19)
Heusler alloys undergoing structural martensite-austenite transformations while
in ferromagnetic state has been performed. From measurements of spontaneous
magnetization, Ms(T), jumps \Delta M at structural phase transitions were
determined. Virtual Curie temperatures of the martensite were estimated from
the comparison of magnetization in martensitic and austenitic phases. Both
saturation magnetic moments in ferromagnetic state and effective magnetic
moments in paramagnetic state of Mn and Ni atoms were estimated and the
influence of delocalization effects on magnetism in these alloys was discussed.
The experimental results obtained show that the shift of martensitic transition
temperature depends weakly on composition. The values of this shift are in good
correspondence with Clapeyron-Clausius formalism taking into account the
experimental data on latent heat at martensite-austenite transformations.Comment: 7 pages, 8 figure
Low-loss Si-based Dielectrics for High Frequency Components of Superconducting Detectors
Silicon-based dielectric is crucial for many superconducting devices,
including high-frequency transmission lines, filters, and resonators. Defects
and contaminants in the amorphous dielectric and at the interfaces between the
dielectric and metal layers can cause microwave losses and degrade device
performance. Optimization of the dielectric fabrication, device structure, and
surface morphology can help mitigate this problem. We present the fabrication
of silicon oxide and nitride thin film dielectrics. We then characterized them
using Scanning Electron Microscopy, Atomic Force Microscopy, and
spectrophotometry techniques. The samples were synthesized using various
deposition methods, including Plasma-Enhanced Chemical Vapor Deposition and
magnetron sputtering. The films morphology and structure were modified by
adjusting the deposition pressure and gas flow. The resulting films were used
in superconducting resonant systems consisting of planar inductors and
capacitors. Measurements of the resonator properties, including their quality
factor, were performed.Comment: 4 pages, 5 figures, conferenc
SPT-3G: A Next-Generation Cosmic Microwave Background Polarization Experiment on the South Pole Telescope
We describe the design of a new polarization sensitive receiver, SPT-3G, for
the 10-meter South Pole Telescope (SPT). The SPT-3G receiver will deliver a
factor of ~20 improvement in mapping speed over the current receiver, SPTpol.
The sensitivity of the SPT-3G receiver will enable the advance from statistical
detection of B-mode polarization anisotropy power to high signal-to-noise
measurements of the individual modes, i.e., maps. This will lead to precise
(~0.06 eV) constraints on the sum of neutrino masses with the potential to
directly address the neutrino mass hierarchy. It will allow a separation of the
lensing and inflationary B-mode power spectra, improving constraints on the
amplitude and shape of the primordial signal, either through SPT-3G data alone
or in combination with BICEP-2/KECK, which is observing the same area of sky.
The measurement of small-scale temperature anisotropy will provide new
constraints on the epoch of reionization. Additional science from the SPT-3G
survey will be significantly enhanced by the synergy with the ongoing optical
Dark Energy Survey (DES), including: a 1% constraint on the bias of optical
tracers of large-scale structure, a measurement of the differential Doppler
signal from pairs of galaxy clusters that will test General Relativity on ~200
Mpc scales, and improved cosmological constraints from the abundance of
clusters of galaxies.Comment: 21 pages, 9 figures. To be published in Proceedings of SPIE Volume
9153. Presented at SPIE Astronomical Telescopes + Instrumentation 2014,
conference 915
Design and Bolometer Characterization of the SPT-3G First-year Focal Plane
During the austral summer of 2016-17, the third-generation camera, SPT-3G,
was installed on the South Pole Telescope, increasing the detector count in the
focal plane by an order of magnitude relative to the previous generation.
Designed to map the polarization of the cosmic microwave background, SPT-3G
contains ten 6-in-hexagonal modules of detectors, each with 269 trichroic and
dual-polarization pixels, read out using 68x frequency-domain multiplexing.
Here we discuss design, assembly, and layout of the modules, as well as early
performance characterization of the first-year array, including yield and
detector properties.Comment: Conference proceeding for Low Temperature Detectors 2017. Accepted
for publication: 27 August 201
CMB Polarization B-mode Delensing with SPTpol and Herschel
We present a demonstration of delensing the observed cosmic microwave
background (CMB) B-mode polarization anisotropy. This process of reducing the
gravitational-lensing generated B-mode component will become increasingly
important for improving searches for the B modes produced by primordial
gravitational waves. In this work, we delens B-mode maps constructed from
multi-frequency SPTpol observations of a 90 deg patch of sky by subtracting
a B-mode template constructed from two inputs: SPTpol E-mode maps and a lensing
potential map estimated from the map of the
CIB. We find that our delensing procedure reduces the measured B-mode power
spectrum by 28% in the multipole range ; this is shown to be
consistent with expectations from theory and simulations and to be robust
against systematics. The null hypothesis of no delensing is rejected at . Furthermore, we build and use a suite of realistic simulations to
study the general properties of the delensing process and find that the
delensing efficiency achieved in this work is limited primarily by the noise in
the lensing potential map. We demonstrate the importance of including realistic
experimental non-idealities in the delensing forecasts used to inform
instrument and survey-strategy planning of upcoming lower-noise experiments,
such as CMB-S4.Comment: 17 pages, 10 figures. Comments are welcome
Measurements of Sub-degree B-mode Polarization in the Cosmic Microwave Background from 100 Square Degrees of SPTpol Data
We present a measurement of the -mode polarization power spectrum (the
spectrum) from 100 of sky observed with SPTpol, a
polarization-sensitive receiver currently installed on the South Pole
Telescope. The observations used in this work were taken during 2012 and early
2013 and include data in spectral bands centered at 95 and 150 GHz. We report
the spectrum in five bins in multipole space, spanning the range , and for three spectral combinations: 95 GHz 95 GHz, 95
GHz 150 GHz, and 150 GHz 150 GHz. We subtract small ( in units of statistical uncertainty) biases from these spectra and
account for the uncertainty in those biases. The resulting power spectra are
inconsistent with zero power but consistent with predictions for the
spectrum arising from the gravitational lensing of -mode polarization. If we
assume no other source of power besides lensed modes, we determine a
preference for lensed modes of . After marginalizing over
tensor power and foregrounds, namely polarized emission from galactic dust and
extragalactic sources, this significance is . Fitting for a single
parameter, , that multiplies the predicted lensed -mode
spectrum, and marginalizing over tensor power and foregrounds, we find
, indicating that our measured spectra are
consistent with the signal expected from gravitational lensing. The data
presented here provide the best measurement to date of the -mode power
spectrum on these angular scales.Comment: 21 pages, 4 figure
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