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

Low frequency noise in current biased La0.82Ca0.18MnO3 single crystals has been investigated in a wide temperature range from 79 to 290 K. Despite pronounced changes in the magnetic properties and dissipation mechanisms of the sample with changing temperature, the noise spectra were found to be always of the 1/f type, and their intensity (except for the lowest temperature studied) scaled as the square of the bias. At liquid nitrogen temperatures and under a bias exceeding some threshold value, the behavior of the noise deviates from the quasiequilibrium modulation noise and starts to depend in a nonmonotonic way on the bias. It has been verified that the observed noise obeys the Dutta and Horn model of 1/f noise in solids. The appearance of nonequilibrium 1/f noise and its dependence on bias have been associated with changes in the distribution of activation energies in the underlying energy landscape. These changes have been correlated with bias induced changes in the intrinsic tunneling mechanism domina...