  We have studied the room-temperature magnetoimpedance of paramagnetic (x =
0.06) and ferromagnetic (x = 0.1) samples in La0.7Ca0.3-xSrxMnO3 series using a
radio-frequency impedance analyzer and also microwave power absorption using a
network analyzer. In both measurements, samples were enclosed tightly inside a
copper stripcoil and impedance or reflection coefficient of this copper
stripcoil was measured as a function of the applied magnetic field for
different frequencies of current (f = 0.1 to 2.5 GHz). The direction of the
applied magnetic field was perpendicular to the alternating magnetic field
produced by the coil. In the ferromagnetic sample (x = 0.1), magnetoresistance
shows a peak around zero field for lower frequencies but a peak appears at H
away from the origin at higher frequencies. The position of the peak shifts
towards higher fields with increasing frequency. A similar trend is also found
for the paramagnetic sample (x = 0.06) but the peak occurs at a higher field
compared to the ferromagnetic sample for the same frequency. Microwave power
absorption also shows features similar to magnetoresistance. Line shape
analysis of the data was performed by fitting the data to a Lorentzian
function. It is concluded that the observed features are imprints of
ferromagnetic resonance in x = 0.1 and paramagnetic resonance in x = 0.06
samples.
