Abstract
We have investigated magnetically tunable AC electrical properties of (100-x)% La0.7Sr0.3MnO3 (LSMO) - x% Paraffin wax (weight%, x = 0.05, 0.1, 0.2 and 1.0) hybrid nanocomposites prepared through a chemical pyrophoric reaction technique at room temperature. The electric field applied across the composites is at perpendicular direction with applied magnetic field(H). The impedance(Z) of the samples is found to decrease with increase in H at low frequency regime indicating the presence of field dependent electrical relaxation process in the system. The decrement of Z with applied H is supposed to be due to gradual depinning of magnetic domain walls from the grain boundary pinning centres thereby enhancing the spin dependent transport in the composites. Nyquist plots have been fitted using parallel combinations of both grain and grain boundaries resistance and capacitance. The grain (grain boundary) resonance frequency fRG(fRGB) is observed to shift towards lower (higher) frequency region with H. This opposite variation of fRG and fRGB with H reveals evidence of two competing factors namely H induced enhancement of inductive part and H enhanced spin dependent transport causing fast relaxation processes in the system. Both fRG and fRGB are found to increase with Paraffin wax concentration upto 0.1% and 0.2% respectively. But both of them show a decreasing trend with further increase of Paraffin wax concentration to 1.0%. We have attributed this anomalous variation to multiple factors like increase in thickness of spin polarized Paraffin wax tunnel barrier with Paraffin wax and enhancement of Mn2O3 impurity phase in nanocomposites with 0.1% and 0.2% Paraffin wax concentration. Systematic decrease of RG observed with H is attributed to suppression of spin fluctuation by magnetic field within grains whereas observed increase in CG with H is expected due to some magnetocapacitive coupling in the grain of the samples. Systematic decrease of RGB observed with H is attributed to depinning of GB domain walls with H, from GB pinning wells whereas observed increase in CGB with H is expected due to presence of inhomogeneous Paraffin wax interface in the samples.
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