170 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
A Historical Review of Diachrony and Semantic Dimensions of Trace in Neurosciences and Lacanian Psychoanalysis.
Experience leaves a trace in the nervous system through plasticity. However, the exact meaning of the mnesic trace is poorly defined in current literature. This article provides a historical review of the term trace in neuroscience and psychoanalysis literature, to highlight two relevant aspects: the diachronic and the semantic dimensions. There has been a general interest in diachrony, or a form of evolution of the trace, but its indissociable semantic dimension remains partially disregarded. Although frequently implied, the diachronic and semantic dimensions of the trace are rarely clearly articulated. We situate this discussion into the classical opposition of syntax, or rules of inscription of the trace in the nervous system, and semantics, or the content of the trace, which takes into consideration the attempt of the human being to build coherence. A general observation is that the study of the term trace follows trends of the thought of the given epoch. This historical analysis also reveals the decay of the idea that the trace is reliable to the experience. From the articulation between neurosciences and psychoanalysis in a historical perspective, this review shows that the trend is to consider trace as a production of the subject, resulting in a permanent rewriting in an attempt to give meaning to the experience. This trend is becoming increasingly evident in light of recent research in neurosciences and psychoanalysis
Ferrimagnetism of the magnetoelectric compound CuOSeO probed by Se NMR
We present a thorough Se NMR study of a single crystal of the
magnetoelectric compound CuOSeO. The temperature dependence of the
local electronic moments extracted from the NMR data is fully consistent with a
magnetic phase transition from the high-T paramagnetic phase to a low-T
ferrimagnetic state with 3/4 of the Cu ions aligned parallel and 1/4
aligned antiparallel to the applied field of 14.09 T. The transition to this
3up-1down magnetic state is not accompanied by any splitting of the NMR lines
or any abrupt modification in their broadening, hence there is no observable
reduction of the crystalline symmetry from its high-T cubic \textit{P}23
space group. These results are in agreement with high resolution x-ray
diffraction and magnetization data on powder samples reported previously by Bos
{\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean
field theory description of the problem based on a microscopic spin Hamiltonian
with one antiferromagnetic ( K) and one ferromagnetic
( K) nearest-neighbor exchange interaction
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
Orbital domain state and finite size scaling in ferromagnetic insulating manganites
55Mn and 139La NMR measurements on a high quality single crystal of
ferromagnetic (FM) La0.80Ca20MnO3 demonstrate the formation of localized
Mn(3+,4+) states below 70 K, accompanied with strong anomalous increase of
certain FM neutron Bragg peaks. (55,139)(1/T1) spin-lattice relaxation rates
diverge on approaching this temperature from below, signalling a genuine phase
transition at T(tr) approx. 70 K. The increased local magnetic anisotropy of
the low temperature phase, the cooling-rate dependence of the Bragg peaks, and
the observed finite size scaling of T(tr) with Ca (hole) doping, are suggestive
of freezing into an orbital domain state, precursor to a phase transition into
an inhomogeneous orbitally ordered state embodying hole-rich walls.Comment: 4 pages, 4 figure
Toxic effects of estradiol E2 on development in the European tree frog (Hyla arborea)
Estrogenic hormones are a major environmental threat to aquatic wildlife. Here we report chronic toxic effects of exposure to the naturally excreted estrogen, 17β-estradiol (E2), on the larval and subadult development of the European tree frog (Hyla arborea), by an experimental setting and long-term monitoring. In addition to the documented impact on sexual development and mating behavior, the general toxicity of human-released estrogens may contribute to global amphibian declines
Template nanowires for spintronics applications: nanomagnet microwave resonators functioning in zero applied magnetic field
Low-cost spintronic devices functioning in zero applied magnetic field are
required for bringing the idea of spin-based electronics into the real-world
industrial applications. Here we present first microwave measurements performed
on nanomagnet devices fabricated by electrodeposition inside porous membranes.
In the paper, we discuss in details a microwave resonator consisting of three
nanomagnets, which functions in zero external magnetic field. By applying a
microwave signal at a particular frequency, the magnetization of the middle
nanomagnet experiences the ferromagnetic resonance (FMR), and the device
outputs a measurable direct current (spin-torque diode effect). Alternatively,
the nanodevice can be used as a microwave oscillator functioning in zero field.
In order to test the resonators at microwave frequencies, we developed a simple
measurement set-up.Comment: 21 pages (main text - 13 pages + Supporting Information
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
Spin-dependent charge transfer at chiral electrodes probed by magnetic resonance
Chirality-induced spin selectivity is evidenced by exciting the spin resonance of radicals in an electrochemical cell where the working electrode is covered with a chiral self-assembled monolayer. Because the electron transfer to and from the paramagnetic radical is spin dependent, the electrochemical current changes at resonance. This electrically-detected magnetic resonance (EDMR) is monitored by a lock-in detection based on electrode voltage modulation, at a frequency that optimizes the sensitivity of the differential conductance to the electrode charge transfer process. The method is validated using p-doped GaAs electrodes in which the conduction band electrons are hyperpolarized by a well-known method of optical spin pumping with circularly polarized light. Gold electrodes covered with peptides consisting of 5 alanine groups (Al5) present a relative current change of up to 5 × 10-5 when the resonance condition is met, corresponding to a spin filtering efficiency between 6 and 19%
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