High-frequency magnetotransport in La1-xSrxMnO3 (x = 0.12-0.20)

Abstract

We report the magnetization, magnetic field dependence of direct current magnetoresistance (dc MR) and alternating current magnetoresistance (ac MR) in La1-xSrxMnO3 (x = 0.12, 0.18, and 0.20) in the frequency range f= 30 MHz to 3000 MHz, at room temperature. The ac MR is negative in all three compositions and shows a dramatic increase in magnitude compared to the dc MR when f = 30 MHz and in a magnetic field H = ±3 kOe. With increasing frequency of current, the sign of ac MR at 3 kOe progressively changes from negative to positive in all these samples which is initiated by appearance of two peaks at H = ±Hr. Line shape analysis of the data indicate that Hr increases linearly with f in x = 0.12 and 0.18. We attribute the two peak behavior at high frequencies to electron paramagnetic resonance in x = 0.12 and 0.18 samples. From the analysis, we obtain the gyromagnetic ratio γ/2π = 2.428 MHz/Oe and 2.690 MHz/Oe for x = 0.18 and 0.12 respectively. The smaller value of γ/2π in x = 0.18 possibly reflects short-range correlations among Mn-spins in the paramagnetic state.