  We have investigated magnetic field dependence of the ac magnetoresitance and
the magnetoreactance in La0.67Ba0.33MnO3 over a wide frequency range from f = 0
to 30 MHz. A huge ac magnetoresistance of 55 % at f = 15 MHz in a small
magnetic field of H = 100 mT and magnetoreactance of 80 % at 2 MHz are
reported. We show distinct field dependence of the magnetoreactance and the
magnetoresistance with increasing frequency. It is shown that while the ac
magnetoresistance is negative and shows a single peak at the origin for all
frequencies except f = 30 MHz, the single peak in the magnetoreactance
transforms into a valley at the origin and simultaneously a double peak
develops . The position of the double peak increases in field with increasing
frequency. Eventually, the sign of the magnetoreactance changes from negative
to positive. Our results indicate possible occurrence of the ferromagneic
resonance in MHz range in unsaturated manganite.
