Anomalous alternating current magnetoresistance in La0.5Ca 0.5Mn1-xNixO3 (x=0.04)

Abstract

We report the magnetic field and temperature dependences of ac electrical transport in La0.5Ca0.5 Mn0.96Ni 0.04O3 as a function of frequency. The ac magnetoresistance shows an anomalous behavior as a function of field: it is negative and exhibits a bell shaped curve about the origin (H=0 T) at f=0.1 MHz, but it transforms into a valley at the origin (accompanied by a positive peak on either side of the origin) for f≥3 MHz at T 125 K. With increasing frequency, the depth of the valley increases and the position of the peak shifts toward higher field. However, the magnetoreactance is negative and exhibits only a single peak at the origin for all temperatures and frequencies. At T=125 K and f=5 MHz, a magnetoresistance of 80 and a magnetoreactance of -90 were found for H 2 T. These results are very different from those for La 0.7Sr0.3MnO3, and we discuss the possible origins of the observed anomalous ac magnetotransport in this compound. © 2011 American Institute of Physics.