Spatial dependence of magnetoimpedance in La0.67Ba0.33MnO3

We investigated magnetic field dependence of radio frequency magnetoimpedance in La0.67Ba0.33MnO3 at room temperature. Both ac magnetoresistance (ΔR/R) and magnetoreactance (ΔX/X) were measured as a function of frequency (f=0.5–30MHz) and magnetic field (−100mT<μ0H<100mT). It is shown that the magnitudes of both ΔR/R and ΔX/X are dependent on the distance (lv)(lv) between the voltage probes for a fixed length of the sample contrary to dc magnetoresistance. The magnitude of ΔR/R at a low magnetic field μ0H=100mT decreases from 55% for lv=6.5mm to 38% for lv=1.5mm. Although ΔX/X decreases with decreasing lvlv, (ΔX/X) per unit lvlv remains nearly the same for all lvlvs. We suggest that the spatial dependence of the observed magnetoimpedance effect is due to local variations in the magnetic permeability and electrical conductivity between ferromagnetic grains. Our results suggest that high frequency electrical magnetotransport can be used to spatially map local electromagnetic response in manganites.