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

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

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