Low frequency 1/f noise in doped manganite grain-boundary junctions

TL;DR

This study investigates the low frequency 1/f noise in grain boundary junctions of doped manganite films, revealing magnetic fluctuations as the primary noise source and characterizing their behavior at low temperatures.

Contribution

It provides a systematic analysis linking magnetic fluctuations to 1/f noise in manganite grain boundary junctions, highlighting the role of localized magnetic sites and clusters.

Findings

1/f noise is dominated by magnetic fluctuations in the grain boundary.

Lorentzian components indicate fluctuating magnetic clusters at low temperature.

Domain fluctuations in electrodes are not significant noise sources.

Abstract

We have performed a systematic analysis of the low frequency 1/f-noise in single grain boundary junctions in the colossal magnetoresistance material La_{2/3}Ca_{1/3}MnO_{3-delta}. The grain boundary junctions were formed in epitaxial La_{2/3}Ca_{1/3}MnO_{3-delta} films deposited on SrTiO_3 bicrystal substrates and show a large tunneling magnetoresistance of up to 300% at 4.2 K as well as ideal, rectangular shaped resistance versus applied magnetic field curves. Below the Curie temperature T_C the measured 1/f noise is dominated by the grain boundary. The dependence of the noise on bias current, temperature and applied magnetic field gives clear evidence that the large amount of low frequency noise is caused by localized sites with fluctuating magnetic moments in a heavily disordered grain boundary region. At 4.2 K additional temporally unstable Lorentzian components show up in the noise spectra that are most likely caused by fluctuating clusters of interacting magnetic moments. Noise due to fluctuating domains in the junction electrodes is found to play no significant role.