Ac magnetotransport in La0.7Sr0.3Mn0.95Fe0.05O3 at low dc magnetic fields

We report the ac electrical response of La0.7Sr0.3Mn1-xFexO3 (x = 0.05) as a function of temperature, magnetic field (H) and frequency of radio frequency (rf) current (f = 0.1-20 MHz). The ac impedance (Z) was measured while rf current directly passes through the sample as well as in a coil surrounding the sample. It is found that with increasing frequency of the rf current, Z(T) shows an abrupt increase accompanied by a peak at the ferromagnetic Curie temperature. The peak decreases in magnitude and shifts down with increasing value of H. We find a magnetoimpedance of Delta Z/Z = -21% for Delta H = 500 Oe at f = 1 MHz around room temperature when the if current flows directly through the sample and Delta Z/Z = -65.9% when the if current flows through a coil surrounding the sample. It is suggested that the magnetoimpedance observed is a consequence of suppression of transverse permeability which enhances skin depth for current flow. Our results indicate that the magnetic field control of high frequency impedance of manganites is more useful than direct current magnetoresistance for low-field applications. (C) 2011 Elsevier Ltd. All rights reserved.