Huge ac magnetoresistance of La0.7Sr0.3MnO3 in subkilogauss magnetic fields

Abstract

We report the electrical and magnetotransport behavior of a ferromagnetic metallic oxide, La0.7Sr0.3MnO3, in response to radio frequency current passing through the sample. We have studied the temperature dependence of the ac resistance (R) and inductive reactance (X) under different dc bias magnetic fields (Hdc=0–1 kOe) for different frequencies (f) of radio frequency current from f=0.1 to 5 MHz. The zero field R, which decreases smoothly around the Curie temperature TC for f=100 kHz, transforms into a peak for f=0.5–5 MHz. The peak decreases in amplitude, broadens, shifts downward in temperature as the bias field increases, and is completely suppressed under Hdc=1 kOe when f=0.5 MHz. The ac magnetoresistance and magnetoinductance exhibit a peak close to the TC. A huge low-field ac magnetoresistance (ΔR/R=40%) and magnetoinductance (ΔX/X=12%) are found in a field of Hdc=700 Oe and f=2 MHz. It has been suggested that the observed ac magnetoresistance has its origin in the suppression of spin fluctuation near TC and the enhancement of magnetic skin depth under the external magnetic field. The huge ac magnetoresistance reported in this work can be exploited for magnetic field sensors and other applications.