Thermal hysteresis in low-frequency noise of La0.7Sr0.3Mn0.92Fe0.08O 3 thin films at low magnetic field

Abstract

The low-frequency 1/f voltage noise of epitaxial La0.7Sr0.3Mn0.92Fe0.08O 3 thin films has been studied as a function of temperature (80-300 K) and magnetic field (up to 1500 G). It is found that the noise power spectral density (PSD) shows a peak at T ≈ 238 K which coincides with the peak temperature of the resistivity, and is below the Curie temperature. When a small magnetic field of 1500 G is applied, the noise PSD shows a large thermal hysteresis and changes with the magnetic history. This thermal hysteresis, lacking at B = 0, is distinctively different from other reported results on manganites without Mn-site doping. The origin of the noise peak at B = 0 is analysed on the basis of the magnetic fluctuation, and the scaling analysis of the normalized noise PSD is consistent with a three-dimensional random-void percolation model. The thermal hysteresis of the noise PSD further supports the assertions of a contribution from magnetic fluctuations and of a spin-dependent conduction process in Fe-doped colossal-magnetoresistance materials.