Unusual field dependence of radio frequency magnetoimpedance in La_0.67Ba_0.33MnO₃

Department of Physics and NUS Nanoscience & Nanotechnology Initiative (NUSNNI), Faculty of Science, National university of Singapore - 2 Science Drive 3, Singapore 117542, Singapore

Corresponding author: phyrm@nus.edu.sg

Received: 24 November 2008
Accepted: 30 March 2009

Abstract

Magnetic-field dependence of the ac impedance in La_0.67Ba_0.33MnO₃ carried out over a wide frequency range ( to 30 MHz) reveals a huge low-field ac magnetoresistance, ΔR/R = -55% at f = 15 MHz and magnetoreactance, ΔX/X = -80% at f = 3 MHz in = 100 mT at room temperature. We show contrasting evolution of ΔR/R and ΔX/X with increasing magnetic field and frequency. While ΔR/R is negative and shows a single peak at = 0 T for all but f = 30 MHz, the single peak in ΔX/X transforms into a valley at the origin and a double peak at H = ±H_k which shifts upward in H with increasing frequency. The ΔX/X eventually changes sign from negative to positive above 25 MHz. The observed features in ΔX/X suggest possible occurrence of ferromagnetic resonance in MHz range.