8,237 research outputs found
Magnetic and magnetoelectric studies in pure and cation doped BiFeO3
We report magnetic and magnetoelectric studies on BiFeO3 and divalent cation
(A) suvtitute Bi0.7A0.3FeO3 (A = Sr,Ba, and Sr0.5Ba0.5). It is shown that the
rapid increase of magnetization at the Neel temperature (TN = 642 K) is
suppressed in the co-doped compound A = Sr0.5Ba0.5. All the divalent subtituted
compounds show enhanced magnetization and hysteresis loop. Both longitudinal
and transverse magnetoelectric coefficients were measured using the dynamical
lock-in technique. The co-doped compound shows the highest magnetoelectric
coefficient at room temperature although it is not the compound with the
highest saturation magnetization. It is found that as the size of the A-site
cation increses, the transverse magnetoelectric coeffient increases and exceeds
the longitudinal magnetoelectric coefficient. It is suggested that changes in
magnetic domain structure and magnetostriction are possible reasons for the
observed changes in the magnetoelectric coefficients.Comment: 16 pages, 6 figur
Electrical, magnetic, magnetodielectric and magnetoabsorption studies in multiferroic GaFeO3
We report electrical, magnetic, magnetodielectric and magnetoabsorption
properties of a polycrystalline GaFeO3. The resistivity measurement shows that
the sample is highly insulating below 200 K and the resistivity above 200 K
obey the Arrhenius law with an activation energy of Ea = 0.67 eV. An anomaly
occurs in the temperature dependence of permittivity (e) near the ferrimagnetic
transition temperature (TC = 228 K) in a zero magnetic field and it is
suppressed under H = 60 mT which indicates a possible magnetoelectric coupling
in GaFeO3 with a fractional change of de/e = -1.8% at 60 mT around TC. The
coercivity (HC) of the sample increases dramatically with lowering temperature
below 200 K from 0.1 T at 200 K to 0.9 T at 5 K. Magnetoabsorption was studied
with a LC resonance technique and we found a close correlation between the
shift in the resonance frequency due to applied magnetic field and the coercive
field measured using dc magnetization measurements. Our results obtained with
multiple techniques suggest that GaFeO3 is an interesting ferrimagnet with
potential applications in future multiferroic devices.Comment: 22 pages, 6 figures. submitted to J. Appl. Phy
A large magnetoinductance effect in La0.67Ba0.33MnO3
We report four probe impedance of La0.67Ba0.33MnO3 at f = 100 kHz under
different dc bias magnetic fields. The ac resistance (R) exhibits a peak around
Tp = 325 K which is accompanied by a rapid increase and a peak in the reactance
(X) in a zero field. The magnetoreactance exhibits a sharp peak close to Tp and
its magnitude (= 60% in H = 1 kG) exceeds that of the ac magnetoresistance (= 5
% inH = 1 kG). It is suggested that the magnetoreactance arises from changes in
the self inductance of the sample rather than the capacitance.Comment: 13 pages, 3 figures. accepted in Appl. Phys. Let
Towards developing robust algorithms for solving partial differential equations on MIMD machines
Methods for efficient computation of numerical algorithms on a wide variety of MIMD machines are proposed. These techniques reorganize the data dependency patterns to improve the processor utilization. The model problem finds the time-accurate solution to a parabolic partial differential equation discretized in space and implicitly marched forward in time. The algorithms are extensions of Jacobi and SOR. The extensions consist of iterating over a window of several timesteps, allowing efficient overlap of computation with communication. The methods increase the degree to which work can be performed while data are communicated between processors. The effect of the window size and of domain partitioning on the system performance is examined both by implementing the algorithm on a simulated multiprocessor system
Failure analysis of a graphite/epoxy laminate subjected to bolt bearing loads
Quasi-isotropic graphite/epoxy laminates (T300/5208) were tested under bolt bearing loads to study failure modes, strengths, and failure energy. Specimens had a range of configurations to produce failures by the three nominal failure modes: tension, shearout, and bearing. Radiographs were made after damage onset and after ultimate load to examine the failure modes. Also, the laminate stresses near the bolt hole calculated for each test specimen configuration, and then used with a failure criterion to analyze the test data. Failures involving extensive bearing damage were found to dissipate significantly more energy than tension dominated failures. The specimen configuration influenced the failure modes and therefore also influenced the failure energy. In the width-to-diameter ratio range of 4 to 5, which is typical of structural joints, a transition from the tension mode to the bearing mode was shown to cause a large increase in failure energy. The failure modes associated with ultimate strength were usually different from those associated with the damage onset. Typical damage sequences involved bearing damage onset at the hole boundary followed by tension damage progressing from the hole boundary
COELACHNE GHATICA NAIK, SP. NOV.
Coelachne ghatiea Naik, a new species of grass is described from Western Ghats, India
- …