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 (Delta R/R) and magnetoreactance (Delta X/X) were measured as a function of frequency (f = 0.5-30 MHz) and magnetic field (-100 mT < mu H-0 < 100 mT). It is shown that the magnitudes of both Delta R/R and Delta X/X are dependent on the distance (l(v)) between the voltage probes for a fixed length of the sample contrary to dc magnetoresistance. The magnitude of Delta R/R at a low magnetic field mu H-0 = 100 mT decreases from 55% for l(v) = 6.5 mm to 38% for l(v) = 1.5 mm. Although Delta X/X decreases with decreasing l(v), (Delta X/X) per unit 1 remains nearly the same for all l(v)s. 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. (C) 2010 Elsevier Ltd. All rights reserved.