36,640 research outputs found
Structural, optical, magnetic and electrical properties of Zn1-x Co (x) O thin films
Despite a considerable effort aiming at elucidating the nature of
ferromagnetism in ZnO-based magnetic semiconductor, its origin still remains
debatable. Although the observation of above room temperature ferromagnetism
has been reported frequently in the literature by magnetometry measurement, so
far there has been no report on correlated ferromagnetism in magnetic, optical
and electrical measurements. In this paper, we investigate systematically the
structural, optical, magnetic and electrical properties of Zn1-x Co (x) O:Al
thin films prepared by sputtering with x ranging from 0 to 0.33. We show that
correlated ferromagnetism is present only in samples with x > 0.25. In
contrast, samples with x < 0.2 exhibit weak ferromagnetism only in magnetometry
measurement which is absent in optical and electrical measurements. We
demonstrate, by systematic electrical transport studies that carrier
localization indeed occurs below 20-50 K for samples with x < 0.2; however,
this does not lead to the formation of ferromagnetic phase in these samples
with an electron concentration in the range of 6 x 10(19) cm(-3) 1 x 10(20)
cm(-3). Detailed structural and optical transmission spectroscopy analyses
revealed that the anomalous Hall effect observed in samples with x > 0.25 is
due to the formation of secondary phases and Co clusters.Comment: 28 pages, 8 figure
Suppression of low-energy Andreev states by a supercurrent in YBa_2Cu_3O_7-delta
We report a coherence-length scale phenomenon related to how the high-Tc
order parameter (OP) evolves under a directly-applied supercurrent. Scanning
tunneling spectroscopy was performed on current-carrying YBa_2Cu_3O_7-delta
thin-film strips at 4.2K. At current levels well below the theoretical
depairing limit, the low-energy Andreev states are suppressed by the
supercurrent, while the gap-like structures remain unchanged. We rule out the
likelihood of various extrinsic effects, and propose instead a model based on
phase fluctuations in the d-wave BTK formalism to explain the suppression. Our
results suggest that a supercurrent could weaken the local phase coherence
while preserving the pairing amplitude. Other possible scenarios which may
cause the observed phenomenon are also discussed.Comment: 6 pages, 4 figures, to appear in Physical Review
Swift UVOT Grism Observations of Nearby Type Ia Supernovae - I. Observations and Data Reduction
Ultraviolet (UV) observations of Type Ia supernovae (SNe Ia) are useful tools
for understanding progenitor systems and explosion physics. In particular, UV
spectra of SNe Ia, which probe the outermost layers, are strongly affected by
the progenitor metallicity. In this work, we present 120 Neil Gehrels Swift
Observatory UV spectra of 39 nearby SNe Ia. This sample is the largest UV
(lambda < 2900 A) spectroscopic sample of SNe Ia to date, doubling the number
of UV spectra and tripling the number of SNe with UV spectra. The sample spans
nearly the full range of SN Ia light-curve shapes (delta m(B) ~ 0.6-1.8 mag).
The fast turnaround of Swift allows us to obtain UV spectra at very early
times, with 13 out of 39 SNe having their first spectra observed >~ 1 week
before peak brightness and the earliest epoch being 16.5 days before peak
brightness. The slitless design of the Swift UV grism complicates the data
reduction, which requires separating SN light from underlying host-galaxy light
and occasional overlapping stellar light. We present a new data-reduction
procedure to mitigate these issues, producing spectra that are significantly
improved over those of standard methods. For a subset of the spectra we have
nearly simultaneous Hubble Space Telescope UV spectra; the Swift spectra are
consistent with these comparison data.Comment: Accepted for publication in MNRA
Characteristics of Magnetoplasmas Semiannual Status Report No. 12, May 1 - Oct. 31, 1965
Magnetoplasma characteristics - anomalous diffusion across magnetic field, heat conduction in plasma, cesium plasma generator, and electron velocity distribution function in magnetoplasma
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