Unusual field dependence of radio frequency magnetoimpedance in La0.67Ba0.33MnO3

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.