77 research outputs found
Magneto-impedance of glass-coated Fe-Ni-Cu microwires
The magneto-impedance (MI) of glass-coated Fe-Ni-Cu microwires was
investigated for longitudinal radio-frequency (RF) currents up to a frequency
of 200 MHz using an RF lock-in amplifier method. The MI, defined as DZ/Z =
[Z(H)-Z(H=0.3T)]/Z(H=0.3T), displays a peak structure (negative MI) at zero
field for RF currents with frequencies less than 20MHz and this crosses over to
a sharp dip (positive MI) at higher frequencies. This crossover behavior is
ascribed to the skin-depth-limited response primarily governed by the
field-dependence of the permeability. Large saturation fields (300 to 600 Oe)
and other anomalies indicate the possible influence of giant magneto-resistance
(GMR) on the MI.Comment: 3 pages, 2-column, 3 figures. To be published in J. Appl. Phys. 2000
(44th MMM conference proceedings
Morphology and Magnetic Properties of Sulfonated Poly[styrene-(ethylene/butylene)-styrene]/Iron Oxide Composites
α-Fe2O3 structures were initiated in the sulfonated polystyrene block domains of poly[styrene–(ethylene/butylene)–styrene] (SEBS) block copolymers via a domain-targeted in-situ chemical precipitation method. The crystal structure of these particles was determined using wide-angle X-ray diffraction and selected area electron diffraction using a transmission electron microscope (TEM). TEM revealed that for less sulfonated SEBS (10 mole%), nanoparticles were aggregated with aggregate size range of 100–150 nm whereas for high sulfonation (16 and 20 mole% sSEBS) there were needle-like structures with length and width of 200–250 nm and 50 nm, respectively. Dynamic mechanical analyses suggest that initial iron oxide nanoparticle growth takes place in the sulfonated polystyrene block domains. The magnetic properties of these nanocomposites were probed with a superconducting quantum interference device magnetometer at 5 and 150 K as well as with an alternating gradient magnetometer at 300 K. The materials exhibited superparamagnetism at 150 K and 300 K and ferrimagnetism at 5 K
Charge carrier localization induced by excess Fe in the Fe1+y(Te,Se) superconductor system
We have investigated the effect of Fe nonstoichiometry on properties of the
Fe1+y(Te, Se) superconductor system by means of resistivity, Hall coefficient,
magnetic susceptibility, and specific heat measurements. We find that the
excess Fe at interstitial sites of the (Te, Se) layers not only suppresses
superconductivity, but also results in a weakly localized electronic state. We
argue that these effects originate from the magnetic coupling between the
excess Fe and the adjacent Fe square planar sheets, which favors a short-range
magnetic order.Comment: 15 pages, 6 figures accepted for publication in PR
Incommensurate magnetic order in the alpha-Fe(Te,Se) superconductor systems
Magnetic spin fluctuations is one candidate to produce the bosonic modes that
mediate the superconductivity in the ferrous superconductors. Up until now, all
of the LaOFeAs and BaFe2As2 structure types have simple commensurate magnetic
ground states, as result of nesting Fermi surfaces. This type of
spin-density-wave (SDW) magnetic order is known to be vulnerable to shifts in
the Fermi surface when electronic densities are altered at the superconducting
compositions. Superconductivity has more recently been discovered in
alpha-Fe(Te,Se), whose electronically active antifluorite planes are
isostructural to the FeAs layers found in the previous ferrous superconductors
and share with them the same quasi-two-dimensional electronic structure. Here
we report neutron scattering studies that reveal a unique complex
incommensurate antiferromagnetic order in the parent compound alpha-FeTe. When
the long-range magnetic order is suppressed by the isovalent substitution of Te
with Se, short-range correlations survive in the superconducting phase.Comment: 27 pages, 7 figures, 1 tabl
A spin triplet supercurrent through the half-metallic ferromagnet CrO2
In general, conventional superconductivity should not occur in a ferromagnet,
though it has been seen in iron under pressure. Moreover, theory predicts that
the current is always carried by pairs of electrons in a spin singlet state, so
conventional superconductivity decays very rapidly when in contact with a
ferromagnet, which normally prohibits the existence of singlet pairs. It has
been predicted that this rapid spatial decay would not occur when spin triplet
superconductivity could be induced in the ferromagnet. Here we report a
Josephson supercurrent through the strong ferromagnet CrO2, from which we infer
that it is a spin triplet supercurrent. Our experimental setup is different
from those envisaged in the earlier predictions, but we conclude that the
underlying physical explanation for our result is a conversion from spin
singlet to spin triplets at the interface. The supercurrent can be switched
with the direction of the magnetization, analogous to spin valve transistors,
and therefore could enable magnetization-controlled Josephson junctions.Comment: 14 pages, including 3 figure
Charge-carrier localization induced by excess Fe in the superconductor Fe1+yTe1−xSex
We have investigated the effect of Fe nonstoichiometry on properties of the Fe1+y(Te,Se) superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific-heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity but also results in a weakly localized electronic state. We argue that these effects originate from the magnetic coupling between the excess Fe and the adjacent Fe square-planar sheets, which favors a short-range magnetic order
Charge-carrier localization induced by excess Fe in the superconductor Fe1+yTe1−xSex
We have investigated the effect of Fe nonstoichiometry on properties of the Fe1+y(Te,Se) superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific-heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity but also results in a weakly localized electronic state. We argue that these effects originate from the magnetic coupling between the excess Fe and the adjacent Fe square-planar sheets, which favors a short-range magnetic order
High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe
We have studied the structural and superconducting properties of tetragonal
FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil
cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller
than the rest of Fe based superconductors. At 12GPa we observe a phase
transition from the tetragonal to an orthorhombic symmetry. The high pressure
orthorhombic phase has a higher Tc reaching 34K at 22GPa.Comment: 15 pages, 4 figure
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