We have performed a systematic analysis of the low-frequency $1/f$ noise in single grain-boundary junctions in the colossal magnetoresistance material ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3-\delta }.$ The grain-boundary junctions were formed in epitaxial ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3-\mathrm{\delta }\mathrm{}}$ films deposited on ${\mathrm{SrTiO}}_3$ 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.

• Received 28 August 2002

DOI:https://doi.org/10.1103/PhysRevB.66.224417