Giant magnetoimpedance in Ag-doped La0.7Sr0.3MnO3

Abstract

The resistive and reactive parts of the magnetoimpedance of sintered ferromagnetic samples of La0.7Sr0.3−xAgxMnO3 (x=0.05,0.25) have been measured at room temperature (<Tc) over a frequency interval from 1kHzto15MHz and in the presence of magnetic field up to 4kOe. The field dependence of relative change in resistance [ΔR∕R(0)] is small in the kilohertz region but increases strongly for higher frequency of excitation. The maximum value of [ΔR∕R(0)] at H=4kOe and for ω=15MHz is around 70%. On the contrary the corresponding change in reactance [ΔX∕X(0)] has less frequency sensitivity, and the maximum occurs at ω≈1MHz. The magnetoimpedance is negative for all frequencies. The normalized magnetoimpedance δZ as defined by [Z(H)−Z(0)]∕[Z(0)−Z(4kOe)] when plotted against scaled field H∕H1∕2 is found to be frequency independent; H1∕2 is the field where δZ is reduced to half its maximum. A phenomenological formula for magnetoimpedance, Z(H), in a ferromagnetic material, is proposed based on the Padé approximant. The formula for Z(H) predicts the scaled behavior of δZ.