43 research outputs found
Suspect screening and total oxidizable precursor (TOP) assay as tools for characterization of per- and polyfluoroalkyl substance (PFAS)-contaminated groundwater and treated landfill leachate
Landfill facilities are a major source of release of per- and polyfluoroalkyl substances (PFAS) to the surrounding environment. In this study, landfill leachate treated in a conventional wastewater treatment plant and PFAScontaminated groundwater were subjected to suspect screening analysis and semi-quantification using total oxidizable precursor (TOP) assay and liquid chromatography coupled to high-resolution mass spectrometry (LCHRMS). TOP assays yielded expected results for legacy PFAS and their precursors, but showed no discernible evidence of degradation of perfluoroethylcyclohexane sulfonic acid. TOP assays also produced significant evidence of presence of precursors in both treated landfill leachate and groundwater, but the majority of precursors had probably degraded into legacy PFAS after many years in the landfill. Suspect screening identified a total of 28 PF AS, of which six were not included in the targeted method and were identified with confidence level (CL) ≥3. Semi-quantification of these six compounds showed very low concentrations, indicating that they are not as great a concern as the target PFAS
On the nature of amorphous polymorphism of water
We report elastic and inelastic neutron scattering experiments on different
amorphous ice modifications. It is shown that an amorphous structure (HDA')
indiscernible from the high-density phase (HDA), obtained by compression of
crystalline ice, can be formed from the very high-density phase (vHDA) as an
intermediate stage of the transition of vHDA into its low-density modification
(LDA'). Both, HDA and HDA' exhibit comparable small angle scattering signals
characterizing them as structures heterogeneous on a length scale of a few
nano-meters. The homogeneous structures are the initial and final transition
stages vHDA and LDA', respectively. Despite, their apparent structural identity
on a local scale HDA and HDA' differ in their transition kinetics explored by
in situ experiments. The activation energy of the vHDA-to-LDA' transition is at
least 20 kJ/mol higher than the activation energy of the HDA-to-LDA transition
Experimental observation of an enhanced anisotropic magnetoresistance in non-local configuration
We compare non-local magnetoresistance measurements in multi-terminal Ni
nanostructures with corresponding local experiments. In both configurations,
the measured voltages show the characteristic features of anisotropic
magnetoresistance (AMR). However, the magnitude of the non-local AMR signal is
up to one order of magnitude larger than its local counterpart. Moreover, the
non-local AMR increases with increasing degree of non-locality, i.e., with the
separation between the region of the main current flow and the voltage
measurement region. All experimental observations can be consistently modeled
in terms of current spreading in a non-isotropic conductor. Our results show
that current spreading can significantly enhance the magnetoresistance signal
in non-local experiments
Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films
We correlate simultaneously recorded magnetotransport and spatially resolved
magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films
micropatterned into Hall bars. Room temperature MOKE images reveal the
nucleation and propagation of domains in an externally applied magnetic field
and are used to extract a macrospin corresponding to the mean magnetization
direction in the Hall bar. The anisotropic magnetoresistance calculated using
this macrospin is in excellent agreement with magnetoresistance measurements.
This suggests that the magnetotransport in Heusler compounds can be adequately
simulated using simple macrospin models, while the magnetoresistance
contribution due to domain walls is of negligible importance
Spin Wave Excitation in Magnetic Insulator Thin Films by Spin-Transfer Torque
We describe excitation of dipole-exchange spin waves in insulating magnetic
thin films by spin current injection at the surface of the film. An easy-axis
magnetic surface anisotropy can induce a non-chiral surface spin wave mode with
penetration depth inversely proportional to the strength of the surface
anisotropy, which strongly reduces the critical current and enhances the
excitation power. The importance of the interface spin wave modes on the
excitation spectrum is reduced by spin pumping, which depends on the quality of
the interface as expressed by the spin mixing conductance.Comment: 19 pages, 10 figure
Local charge and spin currents in magnetothermal landscapes
A scannable laser beam is used to generate local thermal gradients in
metallic (Co2FeAl) or insulating (Y3Fe5O12) ferromagnetic thin films. We study
the resulting local charge and spin currents that arise due to the anomalous
Nernst effect (ANE) and the spin Seebeck effect (SSE), respectively. In the
local ANE experiments, we detect the voltage in the Co2FeAl thin film plane as
a function of the laser spot position and external magnetic field magnitude and
orientation. The local SSE effect is detected in a similar fashion by
exploiting the inverse spin Hall effect in a Pt layer deposited on top of the
Y3Fe5O12. Our findings establish local thermal spin and charge current
generation as well as spin caloritronic domain imaging
Giant magnetic anisotropy changes in Sr2CrReO6 thin films on BaTiO3
The integration of ferromagnetic and ferroelectric materials into hybrid
heterostructures yields multifunctional systems with improved or novel
functionality. We here report on the structural, electronic and magnetic
properties of the ferromagnetic double perovskite Sr2CrReO6, grown as epitaxial
thin film onto ferroelectric BaTiO3. As a function of temperature, the
crystal-structure of BaTiO3 undergoes phase transitions, which induce
qualitative changes in the magnetic anisotropy of the ferromagnet. We observe
abrupt changes in the coercive field of up to 1.2T along with resistance
changes of up to 6.5%. These results are attributed to the high sensitivity of
the double perovskites to mechanical deformation.Comment: 3 figure
Epitaxial growth and magnetic properties of Sr2CrReO6 thin films
The double perovskite Sr2CrReO6 is an interesting material for spintronics,
showing ferrimagnetism up to 635 K with a predicted high spin polarization of
about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition
on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum
crystallographic and magnetic properties were obtained by growing at a
substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films
are c-axis oriented, coherently strained, and show less than 20% anti-site
defects. The magnetization curves reveal high saturation magnetization of 0.8
muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic
anisotropy.Comment: accepted for publicatio
Scaling behavior of the spin pumping effect in ferromagnet/platinum bilayers
We systematically measured the DC voltage V_ISH induced by spin pumping
together with the inverse spin Hall effect in ferromagnet/platinum bilayer
films. In all our samples, comprising ferromagnetic 3d transition metals,
Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, V_ISH
invariably has the same polarity. V_ISH furthermore scales with the
magnetization precession cone angle with a universal prefactor, irrespective of
the magnetic properties, the charge carrier transport mechanism or type. These
findings quantitatively corroborate the present theoretical understanding of
spin pumping in combination with the inverse spin Hall effect