41 research outputs found
High-magnetic field phase diagram and failure of magnetic Gr\"uneisen scaling in LiFePO
We report the magnetic phase diagram of single-crystalline LiFePO in
magnetic fields up to 58~T and present a detailed study of magneto-elastic
coupling by means of high-resolution capacitance dilatometry. Large anomalies
at \tn\ in the thermal expansion coefficient imply pronounced
magneto-elastic coupling. Quantitative analysis yields the magnetic Gr\"uneisen
parameter ~mol/J. The positive
hydrostatic pressure dependence ~K/GPa is dominated
by uniaxial effects along the -axis. Failure of Gr\"uneisen scaling below
~K, i.e., below the peak temperature in the magneto-electric
coupling coefficient [\onlinecite{toft2015anomalous}], implies several
competing degrees of freedom and indicates relevance of recently observed
hybrid excitations~[\onlinecite{yiu2017hybrid}]. A broad and strongly
magnetic-field-dependent anomaly in in this temperature regime
highlight the relevance of structure changes. Upon application of magnetic
fields -axis, a pronounced jump in the magnetisation implies
spin-reorientation at ~T as well as a precursing phase at 29~T
and ~K. In a two-sublattice mean-field model, the saturation field
~T enables the determination of the effective
antiferromagnetic exchange interaction ~meV as well as
the anisotropies ~meV and ~meV
Flow cytometry as a rapid analytical tool to determine physiological responses to changing O2 and iron concentration by Magnetospirillum gryphiswaldense strain MSR-1
Magnetotactic bacteria (MTB) are a diverse group of bacteria that synthesise magnetosomes, magnetic membrane-bound nanoparticles that have a variety of diagnostic, clinical and biotechnological applications. We present the development of rapid methods using flow cytometry to characterize several aspects of the physiology of the commonly-used MTB Magnetospirillum gryphiswaldense MSR-1. Flow cytometry is an optical technique that rapidly measures characteristics of individual bacteria within a culture, thereby allowing determination of population heterogeneity and also permitting direct analysis of bacteria. Scatter measurements were used to measure and compare bacterial size, shape and morphology. Membrane permeability and polarization were measured using the dyes propidium iodide and bis-(1,3-dibutylbarbituric acid) trimethine oxonol to determine the viability and âhealthâ of bacteria. Dyes were also used to determine changes in concentration of intracellular free iron and polyhydroxylakanoate (PHA), a bacterial energy storage polymer. These tools were then used to characterize the responses of MTB to different O2 concentrations and iron-sufficient or iron-limited growth. Rapid analysis of MTB physiology will allow development of bioprocesses for the production of magnetosomes, and will increase understanding of this fascinating and useful group of bacteria
Reduction of stored-particle background by a magnetic pulse method at the KATRIN experiment
The KATRIN experiment aims to determine the effective electron neutrino mass with a sensitivity of 0.2 eV/c2 (%90 CL) by precision measurement of the shape of the tritium ÎČ-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. A common background source in this setup is the decay of short-lived isotopes, such as 219Rn and 220Rn, in the spectrometer volume. Active and passive countermeasures have been implemented and tested at the KATRIN main spectrometer. One of these is the magnetic pulse method, which employs the existing air coil system to reduce the magnetic guiding field in the spectrometer on a short timescale in order to remove low- and high-energy stored electrons. Here we describe the working principle of this method and present results from commissioning measurements at the main spectrometer. Simulations with the particle-tracking software Kassiopeia were carried out to gain a detailed understanding of the electron storage conditions and removal processes
Reduction of stored-particle background by a magnetic pulse method at the KATRIN experiment
The KATRIN experiment aims to determine the effective electron neutrino mass with a sensitivity of 0.2 eV/c2 (%90 CL) by precision measurement of the shape of the tritium ÎČ-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. A common background source in this setup is the decay of short-lived isotopes, such as 219Rn and 220Rn, in the spectrometer volume. Active and passive countermeasures have been implemented and tested at the KATRIN main spectrometer. One of these is the magnetic pulse method, which employs the existing air coil system to reduce the magnetic guiding field in the spectrometer on a short timescale in order to remove low- and high-energy stored electrons. Here we describe the working principle of this method and present results from commissioning measurements at the main spectrometer. Simulations with the particle-tracking software Kassiopeia were carried out to gain a detailed understanding of the electron storage conditions and removal processes
Analysis methods for the first KATRIN neutrino-mass measurement
We report on the dataset, data handling, and detailed analysis techniques of the first neutrino-mass measurement by the Karlsruhe Tritium Neutrino (KATRIN) experiment, which probes the absolute neutrino-mass scale via the ÎČ-decay kinematics of molecular tritium. The source is highly pure, cryogenic T2 gas. The ÎČ electrons are guided along magnetic field lines toward a high-resolution, integrating spectrometer for energy analysis. A silicon detector counts ÎČ electrons above the energy threshold of the spectrometer, so that a scan of the thresholds produces a precise measurement of the high-energy spectral tail. After detailed theoretical studies, simulations, and commissioning measurements, extending from the molecular final-state distribution to inelastic scattering in the source to subtleties of the electromagnetic fields, our independent, blind analyses allow us to set an upper limit of 1.1 eV on the neutrino-mass scale at a 90% confidence level. This first result, based on a few weeks of running at a reduced source intensity and dominated by statistical uncertainty, improves on prior limits by nearly a factor of two. This result establishes an analysis framework for future KATRIN measurements, and provides important input to both particle theory and cosmology
Quantitative Long-Term Monitoring of the Circulating Gases in the KATRIN Experiment Using Raman Spectroscopy
The Karlsruhe Tritium Neutrino (KATRIN) experiment aims at measuring the effective electron neutrino mass with a sensitivity of 0.2 eV/c, i.e., improving on previous measurements by an order of magnitude. Neutrino mass data taking with KATRIN commenced in early 2019, and after only a few weeks of data recording, analysis of these data showed the success of KATRIN, improving on the known neutrino mass limit by a factor of about two. This success very much could be ascribed to the fact that most of the system components met, or even surpassed, the required specifications during long-term operation. Here, we report on the performance of the laser Raman (LARA) monitoring system which provides continuous high-precision information on the gas composition injected into the experimentâs windowless gaseous tritium source (WGTS), specifically on its isotopic purity of tritiumâone of the key parameters required in the derivation of the electron neutrino mass. The concentrations c for all six hydrogen isotopologues were monitored simultaneously, with a measurement precision for individual components of the order 10 or better throughout the complete KATRIN data taking campaigns to date. From these, the tritium purity, ΔT, is derived with precision of <10 and trueness of <3 Ă 10, being within and surpassing the actual requirements for KATRIN, respectively