360 research outputs found
Towards wafer scale inductive determination of magnetostatic and dynamic parameters of magnetic thin films and multilayers
We investigate an inductive probe head suitable for non-invasive
characterization of the magnetostatic and dynamic parameters of magnetic thin
films and multilayers on the wafer scale. The probe is based on a planar
waveguide with rearward high frequency connectors that can be brought in close
contact to the wafer surface. Inductive characterization of the magnetic
material is carried out by vector network analyzer ferromagnetic resonance.
Analysis of the field dispersion of the resonance allows the determination of
key material parameters such as the saturation magnetization MS or the
effective damping parameter Meff. Three waveguide designs are tested. The
broadband frequency response is characterized and the suitability for inductive
determination of MS and Meff is compared. Integration of such probes in a wafer
prober could in the future allow wafer scale in-line testing of magnetostatic
and dynamic key material parameters of magnetic thin films and multilayers
Convective blueshift strengths for 242 evolved stars
Context. Extreme precision radial velocity (RV) surveys seeking to detect
planets at RV semi-amplitudes of 10 cm/s are facing numerous challenges. One of
those challenges is convective blueshift caused by stellar granulation and its
suppression through magnetic activity which plays a significant role in hiding
planetary signals in stellar jitter. Aims. Previously we found that for main
sequence stars, convective blueshift as an observational proxy for the strength
of convection near the stellar surface strongly depends on effective
temperature. In this work we investigate 242 post main sequence stars, covering
the subgiant, red giant, and asymptotic giant phases and empirically determine
the changes in convective blueshift with advancing stellar evolution. Methods.
We used the third signature scaling approach to fit a solar model for the
convective blueshift to absorption-line shift measurements from a sample of
coadded HARPS spectra, ranging in temperature from 3750 K to 6150 K. We compare
the results to main sequence stars of comparable temperatures but with a higher
surface gravity. Results. We show that convective blueshift becomes
significantly stronger for evolved stars compared to main sequence stars of a
similar temperature. The difference increases as the star becomes more evolved,
reaching a 5x increase below 4300 K for the most evolved stars. The large
number of stars in the sample, for the first time, allowed for us to
empirically show that convective blueshift remains almost constant among the
entire evolved star sample at roughly solar convection strength with a slight
increase from the red giant phase onward. We discover that the convective
blueshift shows a local minimum for subgiant stars, presenting a sweet spot for
exoplanet searches around higher mass stars, by taking advantage of their
spin-down during the subgiant transition.Comment: 16 pages, 14 figures; accepted for publication in A&
Noble Metal Complexes of a Bis-Caffeine Containing NHC Ligand
N -Heterocyclic carbenes (NHCs) have seen more and more use over the years. The go-to systems that are usually considered are derivatives of benzimidazole or imidazole. Caffeine possesses an imidazole unit and was already utilized as a carbene-type ligand; however, its use within a tridentate bis-NHC system hasâto the best of our knowledgeânot been reported so far. The synthesis of the ligand is straightforward and metal complexes are readily available via silver-salt metathesis. A platinum(II) and a palladium(II) complex were isolated and a crystal structure of the former was examined. For the Pt(II) complex, luminescence is observed in solid state as well as in solution
Organocatalyzed RingâOpening Polymerization of ( S )â3âBenzylmorpholineâ2,5âDione
Abstract A 3âbenzylmorpholineâ2,5âdione monomer is synthesized from the natural amino acid l âphenylalanine and characterized by means of nuclear magnetic resonance and infrared spectroscopy, electrospray ionization mass spectrometry, and elemental analysis. Subsequent to preliminary polymerization studies, a wellâdefined poly(ester amide) homopolymer is synthesized via ringâopening polymerization using a binary catalyst system comprising 1,8âdiazabicyclo[5.4.0]undecâ7âene (DBU) and a 1â(3,5âbis(trifluoromethyl)phenyl)â3âcyclohexylthiourea (TU) cocatalyst with a feed ratio of M/I/DBU/TU = 100/1/1/10. Kinetic studies reveal high controllability of the dispersities and molar masses up to conversions of almost 80%. Analysis by mass spectrometry hints toward excellent endâgroup fidelity at these conditions. In consequence, utilization of hydroxylâfunctionalized poly(ethylene glycol) and poly(2âethylâ2âoxazoline) as macroinitiators results in amphiphilic block copolymers. Bulk miscibility of the building blocks is indicated by differential scanning calorimetry investigations. As more and more promising new drugs are based on hydrophobic molecules featuring aromatic moieties, the novel polyesteramides seem highly promising materials to be used as potential drug delivery vehicles
Tunneling magneto thermo power in magnetic tunnel junction nanopillars
We study the tunneling magneto thermo power (TMTP) in CoFeB/MgO/CoFeB
magnetic tunnel junction nanopillars. Thermal gradients across the junctions
are generated by a micropatterned electric heater line. Thermo power voltages
up to a few tens of \muV between the top and bottom contact of the nanopillars
are measured which scale linearly with the applied heating power and hence with
the applied temperature gradient. The thermo power signal varies by up to 10
\muV upon reversal of the relative magnetic configuration of the two CoFeB
layers from parallel to antiparallel. This signal change corresponds to a large
spin-dependent Seebeck coefficient of the order of 100 \muV/K and a large TMTP
change of the tunnel junction of up to 90%.Comment: Revised version containing additional data and analyis. 13 pages, 3
figure
Hercules X-1: Pulsed gamma-rays detected above 150 GeV
The 1.24 second binary pulsar Her X-1, first observed in X-rays in 1971 by UHURU has now been seen as a sporadic gamma ray source from 1 TeV up to at least 500 TeV. In addition, reprocessed optical and infrared pulses are seen from the companion star HZ Herculis. Thus measurements of the Her X-1/HZ Herculis system span 15 decades in energy, rivaling both the Crab pulsar and Cygnus X-3 in this respect for a discrete galactic source
Determination of spin-dependent Seebeck coefficients of CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars
We investigate the spin-dependent Seebeck coefficient and the tunneling
magneto thermopower of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) in the
presence of thermal gradients across the MTJ. Thermal gradients are generated
by an electric heater on top of the nanopillars. The thermo power voltage
across the MTJ is found to scale linearly with the heating power and reveals
similar field dependence as the tunnel magnetoresistance. The amplitude of the
thermal gradient is derived from calibration measurements in combination with
finite element simulations of the heat flux. Based on this, large
spin-dependent Seebeck coefficients of the order of (240 \pm 110) \muV/K are
derived. From additional measurements on MTJs after dielectric breakdown, a
tunneling magneto thermopower up to 90% can be derived for 1.5 nm MgO based MTJ
nanopillars
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