461 research outputs found
Relaxation of thermo-remanent magnetization in Fe-Cr GMR multilayers
The time decay of the thermo-remanent magnetization (TRM) in Fe-Cr giant
magnetoresistive (GMR) multilayers has been investigated. The magnetization in
these multilayers relaxes as a function of time after being cooled in a small
magnetic field of 100 Oe to a low temperature and then the magnetic field is
switched off. Low-field ( 500 Oe) magnetization studies of these samples
have shown hysteresis. This spin-glass-like behavior may originate from
structural imperfections at the interfaces and in the bulk. We find that the
magnetization relaxation is logarithmic. Here the magnetic viscosity is found
to increase first with increasing temperature, then it reaches a maximum around
T, and then it decreases with increasing temperature. This behavior is
different from that of conventional spin glasses where the logarithmic creep
rate is observed to increase with temperature. Power law also gives good fits
and it is better than the logarithmic fit at higher temperatures. The dynamical
effects of these multilayers are related to the relaxation of thermally blocked
superparamagnetic grains and magnetic domains in the film layers.Comment: 19 page
Coexistence of glassy antiferromagnetism and giant magnetoresistance (GMR) in Fe/Cr multilayer structures
Using temperature-dependent magnetoresistance and magnetization measurements
on Fe/Cr multilayers that exhibit pronounced giant magnetoresistance (GMR), we
have found evidence for the presence of a glassy antiferromagnetic (GAF) phase.
This phase reflects the influence of interlayer exchange coupling (IEC) at low
temperature (T < 140K) and is characterized by a field-independent glassy
transition temperature, Tg, together with irreversible behavior having
logarithmic time dependence below a "de Almeida and Thouless" (AT) critical
field line. At room temperature, where the GMR effect is still robust, IEC
plays only a minor role, and it is the random potential variations acting on
the magnetic domains that are responsible for the antiparallel interlayer
domain alignment.Comment: 5 pages, 4 figure
Effects of oxytetracycline residues in Thai Koi (Anabas testudineus Bloch) collected from Sylhet, Bangladesh
The present study was conducted to determine the levels of oxytetracycline residues in Thai Koi (Anabas testudineus Bloch) collected from some local fish markets of Sylhet Sadar Upazilla, Bangladesh during March to August, 2016. For the purpose of the study, 24 fresh Thai Koi fish samples were randomly collected from four (4) local markets of Sylhet Sadar Upazilla. Concentration of oxytetracycline residues in collected fish samples were determined by High Performance Liquid Chromatography (HPLC) at the Food Toxicology Laboratory of Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhaka. The results showed that 9 (37.50%) samples with detectable amount of oxytetracycline residues (mean = 42.30±3.00 ppb) were found in Thai Koi. Oxytetracycline residues level below detection limit was also reported in 15 (62.50%) samples of Thai Koi during this study. The detected residues of oxytetracycline in this fish sample did not exceed the maximum residue limit (MRL) 100 ppb recommended by the European Commission. Though residue level of oxytetracycline is lower than the MRL but long term exposure could be hazardous for human health. For that reason, control of antibiotic usage in aquaculture, regular residue monitoring, legislations and regulations for the use of antimicrobials in aquaculture and food safety education are utmost things in this regard
A new family of matrix product states with Dzyaloshinski-Moriya interactions
We define a new family of matrix product states which are exact ground states
of spin 1/2 Hamiltonians on one dimensional lattices. This class of
Hamiltonians contain both Heisenberg and Dzyaloshinskii-Moriya interactions but
at specified and not arbitrary couplings. We also compute in closed forms the
one and two-point functions and the explicit form of the ground state. The
degeneracy structure of the ground state is also discussed.Comment: 15 pages, 1 figur
Macroscopic entanglement jumps in model spin systems
In this paper, we consider some frustrated spin models for which the ground
states are known exactly. The concurrence, a measure of the amount of
entanglement can be calculated exactly for entangled spin pairs. Quantum phase
transitions involving macroscopic magnetization changes at critical values of
the magnetic field are accompanied by macroscopic jumps in the (T=0)
entanglement. A specific example is given in which magnetization plateaus give
rise to a plateau structure in the amount of entanglement associated with
nearest-neighbour bonds. We further show that macroscopic entanglement changes
can occur in quantum phase transitions brought about by the tuning of exchange
interaction strengths.Comment: 11 pages, 4 figures, Latex, communicated to Phys. Rev.
Series study of the One-dimensional S-T Spin-Orbital Model
We use perturbative series expansions about a staggered dimerized ground
state to compute the ground state energy, triplet excitation spectra and
spectral weight for a one-dimensional model in which each site has an S=\case
1/2 spin and a pseudospin , representing a doubly
degenerate orbital. An explicit dimerization is introduced to allow study of
the confinement of spinon excitations. The elementary triplet represents a
bound state of two spinons, and is stable over much of the Brillouine zone. A
special line is found in the gapped spin-liquid phase, on which the triplet
excitation is dispersionless. The formation of triplet bound states is also
investigated.Comment: 9 pages, 9 figure
A Honeycomb Proportional Counter for Photon Multiplicity Measurement in the ALICE Experiment
A honeycomb detector consisting of a matrix of 96 closely packed hexagonal
cells, each working as a proportional counter with a wire readout, was
fabricated and tested at the CERN PS. The cell depth and the radial dimensions
of the cell were small, in the range of 5-10 mm. The appropriate cell design
was arrived at using GARFIELD simulations. Two geometries are described
illustrating the effect of field shaping. The charged particle detection
efficiency and the preshower characteristics have been studied using pion and
electron beams. Average charged particle detection efficiency was found to be
98%, which is almost uniform within the cell volume and also within the array.
The preshower data show that the transverse size of the shower is in close
agreement with the results of simulations for a range of energies and converter
thicknesses.Comment: To be published in NIM
Motion of Bound Domain Walls in a Spin Ladder
The elementary excitation spectrum of the spin-
antiferromagnetic (AFM) Heisenberg chain is described in terms of a pair of
freely propagating spinons. In the case of the Ising-like Heisenberg
Hamiltonian spinons can be interpreted as domain walls (DWs) separating
degenerate ground states. In dimension , the issue of spinons as
elementary excitations is still unsettled. In this paper, we study two
spin- AFM ladder models in which the individual chains are
described by the Ising-like Heisenberg Hamiltonian. The rung exchange
interactions are assumed to be pure Ising-type in one case and Ising-like
Heisenberg in the other. Using the low-energy effective Hamiltonian approach in
a perturbative formulation, we show that the spinons are coupled in bound
pairs. In the first model, the bound pairs are delocalized due to a four-spin
ring exchange term in the effective Hamiltonian. The appropriate dynamic
structure factor is calculated and the associated lineshape is found to be
almost symmetric in contrast to the 1d case. In the case of the second model,
the bound pair of spinons lowers its kinetic energy by propagating between
chains. The results obtained are consistent with recent theoretical studies and
experimental observations on ladder-like materials.Comment: 12 pages, 7 figure
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