132 research outputs found
Superconductivity in doped FeTe1-xSx (x= 0.00 to 0.25) single crystals
We report self flux growth and characterization of FeTe1-xSx (x= 0.00 to
0.25) single crystal series. Surface X-ray diffraction (XRD) exhibited
crystalline nature with growth in (00l) plane. Micro-structural (electron
microscopy) images of representative crystals showed the slab-like morphology
and near stoichiometric composition. Powder XRD analysis (Rietveld) of single
crystals exhibited tetragonal structure with P4/nmm space group and decreasing
a and c lattice parameters with increase in x. Electrical resistivity
measurements (R-T) showed superconductivity with Tconset at 9.5K and 8.5K for x
=0.10 and x =0.25 respectively. The un-doped crystal exhibited known step like
anomaly at around 70K. Upper critical field Hc2(0), as calculated from magneto
transport for x =0.25 crystal is around 60Tesla and 45Tesla in H//ab and H//c
directions. Thermal activation energy [U0(H)] calculated for x =0.10 and 0.25
crystals followed weak power law, indicating single vortex pinning at low
fields. Mossbauer spectra for FeTe1-xSx crystals at 300K and 5K are compared
with non superconducting FeTe. Both quadrupole splitting (QS) and isomer shift
(IS) for S doped crystals were found to decrease. Also at 5K the hyperfine
field for x =0.10 superconducting crystal is decreased substantially from
10.6Tesla (FeTe) to 7.2Tesla. For x =0.25 crystal, though small quantity of
un-reacted Fe is visible at room temperature, but unlike x =0.10, the low
temperature (5K) ordered FeTe hyperfine field is nearly zero.Comment: 20 Pages Text + Figs: Accepted Mat. Res. Exp, Mat. Rex. Exp. (2018
Unconventional domain wall magnetoresistance of patterned Ni/Nb bilayer structures below superconducting transition temperature of Nb
Scattering of spin-up and spin-down electrons while passing through a
ferromagnetic domain wall leads to an additional resistance for transport
current, usually observed prominently in constricted magnetic structures. In
this report, we use the resistance of the domain wall as a probe to find
indirect signatures of the theoretically predicted spin-singlet supercurrent to
spin-triplet supercurrent conversion effect of ferromagnetic domain walls. Here
we examine the domain wall induced resistance in Ni stripe in a bilayer Ni/Nb
geometry in the normal state and in the superconducting state of Nb. By making
a 6um wide gap in the top Nb layer we routed the transport current through the
Ni layer in the normal state and in the superconducting state of Nb. In the
normal state of Nb, in-field transport measurements showed a clear domain wall
magneto-resistance (DWMR) peak near the coercive field, where the domain wall
density is expected to be maximum. Interestingly, however, below the
superconducting transition temperature of Nb, the DWMR peak of the Ni layer
showed a sharp drop in the field range where the number of domain walls becomes
maximum. This observation may be a possible signature of magnetic domain wall
induced spin-triplet correlations in the Ni layer due to the direct injection
of spin-singlet Cooper pairs from Nb into the magnetic domain walls
ADVANCED RECEIVER ARCHITECTURES IN RADIOFREQUENCY APPLICATIONS
The general principles of several types of receivers fall under the two main headings of TRF (tuned radio frequency)receivers, where the received signal is processed at the incoming frequency right up to the detector stage, and the superhet(supersonic heterodyne) receiver, where the incoming signal is translated (sometimes after some amplification at theincoming frequency) to an intermediate frequency for further processing. There are however, a number of variants of each ofthese two main types. Regeneration (‘reaction’ or ‘tickling’) may be applied in a TRF receiver, to increase both its sensitivityand selectivity. This may be carried to the stage where the RF amplifier actually oscillates – either continuously, so that thereceiver operates as a synchrodyne or homodyne, or intermittently, so that the receiver operates as a super-regenerativereceiver, both of which have been described previously. The synchrodyne or homodyne may be considered alternatively as asuperhet, where the IF (intermediate frequency) is 0 Hz. In this paper we present the new type of receiver architectureswhich work in radiofrequencies.Keywords: supersonic heterodyne, tuned radio frequency
Heat capacity and Mosssbauer study of Self flux grown FeTe Single Crystal
We report mainly the heat capacity and Mossbauer study of self flux grown
FeTe single crystal, which is ground state compound of the Fe chalcogenides
superconducting series, i.e., FeTe1-x(Se/S)x. The as grown FeTe single crystal
is large enough to the tune of few cm and the same crystallizes in tetragonal
structure having space group of P4/nmm. FeTe shows the structural/magnetic
phase transition at 70K in both magnetic and resistivity measurements. Heat
capacity measurement also confirms the coupled structural/magnetic transition
at the same temperature. The Debye model fitting of low temperature (below 70K)
heat capacity exhibited Debye temperature to be 324K. M\"Ossbauer spectra are
performed at 300K and 5K. The 300K spectra showed two paramagnetic doublets and
the 5K spectra exhibited hyperfine magnetic sextet with an average hyperfine
field of 10.6Tesla matching with the results of Yoshikazu Mizuguchi et al.Comment: Short MS-12 pages text + figs: Accepted Letter - J. Sup. Novel Ma
Study of magnetization reversal in Neel and Bloch regime of Ni and Py stripes using Kerr microscopy
We present a systematic study of the magnetization reversal of nickel and
permalloy micro-stripes with Neel and Bloch domain walls using Kerr microscopy.
Magnetic field driven domain propagation was observed from higher width to
lower width stripes for magnetic fields applied along the length of
micro-stripes. Stripe like domains were observed with nucleation starting in
lower width region followed by their propagation to higher width regions for
magnetic fields applied along the width of micro-stripes. The comparison of
magnetization reversal in Bloch and N\'eel domain wall regime showed higher
domain wall density in Bloch regime for both nickel and permalloy stripes.Comment: 13 pages, 5 figure
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