202 research outputs found
Low temperature hopping magnetotransport in paramagnetic single crystals of cobalt doped ZnO
Long needle-shaped single crystals of Zn1-xCoxO were grown at low
temperatures using a molten salt solvent technique, up to x=0.10. The
conduction process at low temperatures is determined to be by Mott variable
range hopping. Both pristine and cobalt doped crystals clearly exhibit a
crossover from negative to positive magnetoresistance as the temperature is
decreased. The positive magnetoresistance of the Zn1-xCoxO single crystals
increases with increased Co concentration and reaches up to 20% at low
temperatures (2.5 K) and high fields (>1 T). SQUID magnetometry confirms that
the Zn1-xCoxO crystals are predominantly paramagnetic in nature and the
magnetic response is independent of Co concentration. The results indicate that
cobalt doping of single crystalline ZnO introduces localized electronic states
and isolated Co2+ ions into the host matrix, but that the magnetotransport and
magnetic properties are decoupled.Comment: 7 pages, 9 figures, submitted to Physical Review
The phase transition in the localized ferromagnet EuO probed by muSR
We report results of muon spin rotation measurements performed on the
ferromagnetic semiconductor EuO, which is one of the best approximations to a
localized ferromagnet. We argue that implanted muons are sensitive to the
internal field primarily through a combination of hyperfine and Lorentz fields.
The temperature dependences of the internal field and the relaxation rate have
been measured and are compared with previous theoretical predictions.Comment: 4 pages, 4 figure
Current-induced two-level fluctuations in pseudo spin-valves (Co/Cu/Co) nanostructures
Two-level fluctuations of the magnetization state of pseudo spin-valve
pillars Co(10 nm)/Cu(10 nm)/Co(30 nm) embedded in electrodeposited nanowires
(~40 nm in diameter, 6000 nm in length) are triggered by spin-polarized
currents of 10^7 A/cm^2 at room temperature. The statistical properties of the
residence times in the parallel and antiparallel magnetization states reveal
two effects with qualitatively different dependences on current intensity. The
current appears to have the effect of a field determined as the bias field
required to equalize these times. The bias field changes sign when the current
polarity is reversed. At this field, the effect of a current density of 10^7
A/cm^2 is to lower the mean time for switching down to the microsecond range.
This effect is independent of the sign of the current and is interpreted in
terms of an effective temperature for the magnetization.Comment: 4 pages, 5 figures, revised version, to be published in Phys. Rev.
Let
Establishing the fundamental magnetic interactions in the chiral skyrmionic Mott insulator Cu2OSeO3 by terahertz electron spin resonance
The recent discovery of skyrmions in CuOSeO has established a new
platform to create and manipulate skyrmionic spin textures. We use high-field
electron spin resonance (ESR) spectroscopy combining a terahertz free electron
laser and pulsed magnetic fields up to 64 T to probe and quantify its
microscopic spin-spin interactions. Besides providing direct access to the
long-wavelength Goldstone mode, this technique probes also the high-energy part
of the excitation spectrum which is inaccessible by standard low-frequency ESR.
Fitting the behavior of the observed modes in magnetic field to a theoretical
framework establishes experimentally that the fundamental magnetic building
blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled
tetrahedra.Comment: 5 pages, 3 Figure
High performance WR-1.5 corrugated horn based on stacked rings
We present the development and characterisation of a high frequency (500-750
GHz) corrugated horn based on stacked rings. A previous horn design, based on a
Winston profile, has been adapted for the purpose of this manufacturing process
without noticeable RF degradation. A subset of experimental results obtained
using a vector network analyser are presented and compared to the predicted
performance. These first results demonstrate that this technology is suitable
for most commercial applications and also astronomical receivers in need of
horn arrays at high frequencies.Comment: 9 page
Magnetic polarons and the metal-semiconductor transitions in (formula presented) and EuO: Raman scattering studies
We present inelastic light scattering measurements of EuO and (formula presented) (formula presented) 0.005, 0.01, 0.03, and 0.05) as functions of doping, B isotope, magnetic field, and temperature. Our results reveal a variety of distinct regimes as a function of decreasing T: (a) a paramagnetic semimetal regime, which is characterized by a collision-dominated electronic scattering response whose scattering rate (formula presented) decreases with decreasing temperature; (b) a spin-disorder scattering regime, which is characterized by a collision-dominated electronic scattering response whose scattering rate (formula presented) scales with the magnetic susceptibility; (c) a magnetic polaron regime, in which the development of an (formula presented) spin-flip Raman response betrays the formation of magnetic polarons in a narrow temperature range above the Curie temperature (formula presented) and (d) a ferromagnetic metal regime, characterized by a flat electronic continuum response typical of other strongly correlated metals. By exploring the behavior of the Raman responses in these various regimes in response to changing external parameters, we are able to investigate the evolution of charge and spin degrees of freedom through various transitions in these materials. © 2001 The American Physical Society
Spin-dependent transport in cluster-assemblednanostructures: influence of cluster size and matrix material
Abstract.: Spin-dependent transport in granular metallic nanostructures has been investigated by means of a thermoelectric measurement. Cobalt clusters of well-defined size (〈n〉 = 15-600) embedded in copper and silver matrices show magnetic field responses of up to several hundred percent at low temperature. The experimental observations are attributed to spin mixing. The influence of cluster size and matrix are discusse
Magnetic properties of pure and Gd doped EuO probed by NMR
An Eu NMR study in the ferromagnetic phase of pure and Gd doped EuO was
performed. A complete description of the NMR lineshape of pure EuO allowed for
the influence of doping EuO with Gd impurities to be highlighted. The presence
of a temperature dependent static magnetic inhomogeneity in Gd doped EuO was
demonstrated by studying the temperature dependence of the lineshapes. The
results suggest that the inhomogeneity in 0.6% Gd doped EuO is linked to
colossal magnetoresistance. The measurement of the spin-lattice relaxation
times as a function of temperature led to the determination of the value of the
exchange integral J as a function of Gd doping. It was found that J is
temperature independent and spatially homogeneous for all the samples and that
its value increases abruptly with increasing Gd doping.Comment: 14 pages, 10 figures, to be published in Physical Review
Epithelial Sodium Channel-Mediated Sodium Transport Is Not Dependent on the Membrane-Bound Serine Protease CAP2/Tmprss4.
The membrane-bound serine protease CAP2/Tmprss4 has been previously identified in vitro as a positive regulator of the epithelial sodium channel (ENaC). To study its in vivo implication in ENaC-mediated sodium absorption, we generated a knockout mouse model for CAP2/Tmprss4. Mice deficient in CAP2/Tmprss4 were viable, fertile, and did not show any obvious histological abnormalities. Unexpectedly, when challenged with sodium-deficient diet, these mice did not develop any impairment in renal sodium handling as evidenced by normal plasma and urinary sodium and potassium electrolytes, as well as normal aldosterone levels. Despite minor alterations in ENaC mRNA expression, we found no evidence for altered proteolytic cleavage of ENaC subunits. In consequence, ENaC activity, as monitored by the amiloride-sensitive rectal potential difference (ΔPD), was not altered even under dietary sodium restriction. In summary, ENaC-mediated sodium balance is not affected by lack of CAP2/Tmprss4 expression and thus, does not seem to directly control ENaC expression and activity in vivo
Heat and spin transport in magnetic nanowires
Transport measurements are carried out in which temperature oscillation is applied to magnetic nanostructures. Using spin valves, this measurement reveals aspects of the spin transport in non-collinear configurations. In one implementation, an AC voltage is detected when a DC current is driven through the nanostructure under test and its temperature is made to oscillate by illuminating it with a laser diode. A simpler approach is presented that relies on Joule heating to generate the temperature oscillation, thus eliminating the need for any optical component. © 2009 Elsevier Ltd. All rights reserved
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