Low-frequency1/fnoise in doped manganite grain-boundary junctions

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−δ . The grain boundary junctions were formed in epitaxial La 2/3 Ca 1/3 MnO 3−δ 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.

Interface resistive switching effects in bulk manganites

“…There are several different conclusions about the fluctuations in perovskite oxides. In particular, existence of two-level fluctuators is related to the dynamic coexistence of two phases in a phase-separated state, that is, to an electronic origin of the noise [28], or to fluctuating magnetic moments in a heavily disordered grain-boundary region [27], or is explained as a result of oxygen-defect dynamics [29]. The idea of the noise experiment [13] was to compare electrical conductance and noise properties in manganites with totally different electric and magnetic properties.…”

“…[21] and a related analysis of current-voltage characteristics for manganite grain-boundary junctions in Ref. [27]). Thus, it has been shown above that the even part of the differential conductance G(V ) of a thin, inhomogeneous, insulating, metal/manganite interface is a power function of the voltage…”

Bias dependent 1/f conductivity fluctuations in low-doped La1−xCaxMnO3 manganite single crystals

“…12 Current, temperature, and magnetic field dependence of noise in grain boundary junctions, provided clear evidence that 1/f noise is caused by localized states with fluctuating magnetic moments in heavily disordered grain boundary regions. 13 Conductivity noise with 1/f spectrum is generally related to resistance fluctuations which are measured by applying dc current and recorded as voltage fluctuations. When the resistance fluctuations are just probed by current, and not influenced by its flow, then PSD of the noise scales as the square of the bias current.…”

Nonequilibrium 1∕f noise in low-doped manganite single crystals

“…Indeed, S V ∝ V 2 is predicted by the model of 1/f noise in VRH regime. [12] Obviously, in a difference to a discrete fabricated tunnel junction, or to a single grain boundary junction, [6] one cannot provide an absolute direct proof of the tunnel character of the bulk conductivity dominated by distributed intrinsic junctions. Only an indirect evidence can be brought from observations of nonlinear voltagecurrent (V −I) characteristics and their temperature evolution, provided both can be well fitted to a tunneling model.…”

“…[3,4,5] Grain boundary junctions were identified as sources of 1/f noise in manganite thin films. [6] Nongaussian random telegraph fluctuations were ascribed to PS at low temperatures. [7,8] In such complex system as low-doped LCMO one expects that noise data will allow to get a deeper insight into the dynamics of dissipation processes associated with different transport mechanisms.…”