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

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 (< T-c) over a frequency interval from 1 kHz to 15 MHz and in the presence of magnetic field up to 4 kOe. The field dependence of relative change in resistance [Delta R/R(0)] is small in the kilohertz region but increases strongly for higher frequency of excitation. The maximum value of [Delta R/R(0)] at H=4 kOe and for omega=15 MHz is around 70%. On the contrary the corresponding change in reactance [Delta X/X(0)] has less frequency sensitivity, and the maximum occurs at omega approximate to 1 MHz. The magnetoimpedance is negative for all frequencies. The normalized magnetoimpedance delta Z as defined by [Z(H)-Z(0)]/[Z(0)-Z(4 kOe)] when plotted against scaled field H/H-1/2 is found to be frequency independent; H-1/2 is the field where delta Z is reduced to half its maximum. A phenomenological formula for magnetoimpedance, Z(H), in a ferromagnetic material, is proposed based on the Pade approximant. The formula for Z(H) predicts the scaled behavior of delta Z. (c) 2007 American Institute of Physics.