5,034 research outputs found
Current-induced electroresistance in Nd0.5Ca0.5Mn0.95Ni0.05O3
We have investigated the dc and pulsed current-induced electroresistance in
phase separated manganite Nd0.5Ca0.5Mn0.95Ni0.05O3 (NCMONi05) as a function of
temperature and magnetic field. It is shown that the negative differential
resistance which appears above a threshold current (Ic) and hysteresis in the
V-I progressively vanish with increasing period of the current pulses. However
a strong non-linearity in V-I exists even for a pulse period of 6s. The peak
voltage at Ic decreases in magnitude and shifts towards higher current values
with increasing strength of the magnetic field. The strong nonlinear behavior
and the negative differential resistance in the dc current sweep are
accompanied by a rapid increase of the sample surface temperature and therefore
primarily arise from the Joule heating in the sample. While the Joule heating
assists electroresistance in the high dc current regime, the nonlinearity in
the pulsed current sweep and the resistivity switching between a high and low
value induced by controlling the width and period of pulses can not be
explained solely on the basis of Joule heating.Comment: 16 pages,5figures. to appear in Solid State Commu
Influence of length and measurement geometry on magnetoimpedance in La0.7Sr0.3MnO3
We show that ac magnetoresistance at room temperature in La0.7Sr0.3MnO3 is
extremely high (= 47% in H = 100 mT, f = 3-5 MHz), and magnetic field
dependence of reactance exhibits a double peak behavior. However, magnitudes of
the ac magnetoresistance and magnetoreactance for a fixed length of the sample
(li) decrease with decreasing separation (lv) between voltage probes unlike the
dc magnetoresistance. On the contrary, change in li has a negligible influence
on magnetoimpedance when lv is fixed. Our results indicate that high frequency
electrical transport is sensitive to local variations in the magnetic
permeability.Comment: 12 pages, 3 figure
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
Fractal analysis of weld defect patterns obtained by radiographic tests
This paper presents a fractal analysis of radiographic patterns obtained from
specimens with three types of inserted welding defects: lack of fusion, lack of
penetration, and porosity. The study focused on patterns of carbon steel beads
from radiographs of the International Institute of Welding (IIW). The
radiographs were scanned using a greyscale with 256 levels, and the fractal
features of the surfaces constructed from the radiographic images were
characterized by means of Hurst, detrended-fluctuation, and minimal-cover
analyses. A Karhunen-Loeve transformation was then used to classify the curves
obtained from the fractal analyses of the various images, and a study of the
classification errors was performed. The obtained results indicate that fractal
analyses can be an effective additional tool for pattern recognition of weld
defects in radiographic tests.Comment: 7 pages, 2 figures. To appear AIP Conference Proceedings - QNDE 200
Pulse width controlled resistivity switching at room temperature in Bi0.8Sr0.2MnO3
We report pulsed as well as direct current/voltage induced electroresistance
in Bi0.8Sr0.2MnO3 at room temperature. It is shown that bi-level and
multi-level resistivity switching can be induced by a sequence of pulses of
varying pulse width at fixed voltage amplitude. Resistivity increases abruptly
(= 55 % at 300 K) upon reducing pulse width from 100 ms to 25 ms for a fixed
electric field (E = 2 V/cm2) of 200 ms pulse period. The resistivity switching
is accompanied by a periodic change in temperature which alone can not explain
the magnitude of the resistivity change.Comment: 12 pages, 3 figure
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