6,284 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
Magnetically tunable rf wave absorption in polycrystalline La0.67Ba0.33MnO3
We investigated temperature and magnetic field dependent radio-frequency
electromagnetic absorption in La0.67Ba0.33MnO3 by monitoring changes in
resonance frequency (fr) and current (II) through a LC resonant circuit powered
by an integrated chip oscillator. The ferromagnetic to paramagnetic transition
at Tc in zero external magnetic field is accompanied by an abrupt increase in
fr and I and they are tunable by small external magnetic field. We observed
fractional changes as much as 46% in delfr/fr and 23% in delI/I around Tc under
H = 0.1 T that can be exploited for low magnetic field sensors and other
applications.Comment: 12 pages, 5 figure
NOVELTIES IN PANICUM (POACEAE) FROM INDIA
Four novelties in the genus Panicum L. namely P. phoiniclados,P. deccanense and P. paianum together with its variety minor have been described from materials collected from the Marathwada region of the Deecan plateau
Antioxidant-Rich Amaranth Varieties, Arka Samraksha and Arka Varna
Amaranth improvement in India hither to was concerned with development of high-yielding varieties, and hardly any research efforts have been made for its nutritional improvement. Keeping this in view, at Indian Institute of Horticultural Research two high-yielding amaranth varieties, Arka Samraksha and Arka Varna with high antioxidant activity, low amounts of nitrates and oxalates were developed using modified bulk method of selection from segregating population of the crosses IIHR-4 x IIHR-70 and IIHR-7 x IIHR-30 . Arka Samraksha is a high-yielding (10.9 t/ha in 30-35 days), pulling-type variety with green leaves and stem, antioxidant activity of 499mg (AEAC units) and minimum nitrate content of 27.3 mg and 1.34 g oxalates per 100 g fresh leaf weight. Arka Varna also a pulling type, high-yielding variety (10.6 t/ha in 30-35 days) with green leaves and a pink stem, high antioxidant activity of 417 mg (AEAC units), low nitrate content of 37.6 mg and 1.42 g oxalates per 100 g fresh leaf weight
Analysis of Superconducting Fault Current Limiterin DC System with Renewable Energy Sources
Superconducting fault-current limiters (SFCLs) have been the subject of research and development for many years and offer an attractive solution to the problem of rising fault levels in electrical distribution systems. SFCLs can greatly reduce fault currents and the damage at the point of fault, and help improve the stability of a power system. Superconducting fault-current limiters (SFCL) provide a new efficient approach to the reliable handling of such faults.(SCFLs) can be used for various nominal voltages and currents, and can be adapted to particular limiting characteristics in case of short circuits. In this project, dc resistive type superconducting fault current limiter (SFCL) is presented. This SFCL is designed for the HVDC system. Uniform current and voltage sharing among the SFCL modules can be observed through contact resistance tests, dc flow-through tests, and ac flow-through tests. Results of tests show that each limiting module has good uniformity in higher current system. The proposed concept can be implemented using renewable energy sources.The results are presented by using Matlab/Simulink platform
Huge ac magnetoresistance in La0.7Sr0.3MnO3 in sub- kilo gauss magnetic fields
We report dynamical magnetotransport in a ferromagnetic metallic oxide,
La0.7Sr0.3MnO3 using the ac impedance technique. The temperature dependence of
the ac resistance(R) and the inductive reactance (X) of the complex impedance
(Z = R+jX) under different dc bias magnetic fields (Hdc = 0-1 kOe) were studied
for different frequencies f = 0.1 to 5 MHz of alternating current. The zero
field R, which decreases smoothly around the Curie temperature TC for f = 100
kHz, transforms into a peak for f = 0.5-5 MHz. The peak decreases in amplitude,
broadens and shifts downward in temperature as the bias field increases. A huge
ac magnetoresistance (= 45 % at f = 2 MHz) in a field of Hdc = 1 kOe is found
and we attribute it to the magnetic field- induced enhancement in the skin
depth and concomitant suppression of magnetic fluctuations near TC. Our study
suggests that radio frequency magnetotransport provides an alternative strategy
to enhance the magnetoresistance and probe the spin-charge coupling in
manganites.Comment: 16 pages, 4 figurea. submitted to Phys. Rev.
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