Abstract
Magnetic-field dependence of the ac impedance Z(f,H)=R(f,H)+jX(f, H) in La0.67Ba0.33MnO3 carried out over a wide frequency range (f=0 to 30 MHz) reveals a huge low-field ac magnetoresistance, ΔR/R=-55% at f=15 MHz and magnetoreactance, ΔX/X=-80% at f=3 MHz in μ0H=100 mT at room temperature. We show contrasting evolution of ΔR/R and ΔX/X with increasing magnetic field and frequency. While ΔR/R is negative and shows a single peak at μ0H=0 T for all but f=30 MHz, the single peak in ΔX/X transforms into a valley at the origin and a double peak at H=±Hk which shifts upward in H with increasing frequency. The ΔX/X eventually changes sign from negative to positive above 25 MHz. The observed features in ΔX/X suggest possible occurrence of ferromagnetic resonance in MHz range.