Dynamical magnetotransport in Ln0.6Sr0.4MnO 3 (Ln = La, Sm)

Abstract

We compare radio frequency electrical transport in Ln0.6Sr 0.4MnO3 (Ln = La and Sm). AC resistance (R) and reactance (X) were simultaneously measured as a function of temperature (T), magnetic field (H), and frequency (f). The R(T, H = 0 G) in La0.6Sr 0.4MnO3 (LSMO) shows a broad insulator-metal transition around 247 K below the Curie temperature (TC) for f ≤ 2 MHz but a steplike increase at TC for f ≥ 3 MHz. Conversely, R(T, H = 0 G) in Sm0.6Sr0.4MnO3 exhibits a single peak at TC 116 ± 2 K for f = 0.1 MHz which splits into two peaks accompanied by a dip at TC for higher frequencies. While the low temperature peak shifts upward rapidly with the increasing H (μ0H 1 T) for f 5 MHz, the high temperature peak is insensitive to the magnetic field. A large ac magnetoresistance (R/R -32) and magnetoreactance (δX/X -21) at a low magnetic field (H 70 mT) is observed in LSMO around TC in contrast to a positive δR/R (170%) and a negative δX/X ( -94%) at μ0H 7 T. We discuss the possible origins of the observed effects. © 2011 American Institute of Physics.