Giant magneto-impedance in Ag-doped La0.7Sr0.3MnO3
  The resistive and reactive parts of the magneto-impedance of sintered ferromagnetic samples of La0.7Sr0.3-xAgxMnO3 (x = 0.05, 0.25) have been measured at room temperature (<Tc) over frequency interval 1KHz to 15MHz and in presence of magnetic field up to 4KOe. The field dependence of relative change in resistance is small in KHz region but increases strongly for higher frequency of excitation. The maximum value of relative change in resistance at H =4KOe was found to be around 70% at 15MHz frequency.On the contrary the corresponding change in reactance has less frequency sensitivity and the maximum occurs at 1MHz frequency. The magneto-impedance is negative for all frequencies. The 'normalized magneto-impedance' as defined by [Z(H)-Z(0)]/[Z(0)-Z(4K)] when plotted against scaled field H/H1/2 is found to be frequency independent ; H1/2 is the field where 'normalized magneto-impedance' is reduced to half its maximum. A phenomenological formula for magneto-impedance Z (H) in ferromagnetic material is proposed based on Pade approximant. The formula for Z (H) predicts the scaled behavior of 'normalized magneto-impedance'. 
S. K. Ghatak, B. Kaviraj, T. K. Dey