Low Frequency Noise in High T C Ferromagnetic La2/3Sr1/3MnO3 Devices: Study of Anomalous Effects Below Curie Temperature

Abstract

Manganite thin films showing colossal magnetoresistance, large resistance change at the metal-to-insulator (M-I) transition temperature and high spin polarization, are promising candidates for a new generation of electronic devices including magnetoresistive sensors, bolometers and spin-valve systems [1, 2, 3]. Among them, ferromagnetic La1 − x Sr x MnO 3 with x ∼ 0.3 (LSMO) attracts especially great attention due to its high Curie temperature value (T C ) of about 360 K, thus creating expectations for the realization of magnetic devices operating at room temperature. To study, understand and reduce the noise level of those compounds is a huge challenge. Here we report detailed investigations of 1/f electrical noise in structures patterned in epitaxial thin films of a large bandwidth La 2/3 Sr 1/3 MnO 3 (LSMO) deposited on (100) SrTiO 3 substrates. The 1/ f noise, which dominate along the whole range of frequencies studies, was observed not to follow the overall temperature dependence of the resistivity as shown by other LSMO film in literature [4]. Moreover no significant dependence of the 1/f noise with the temperature (above 300 K) could be observed, which seems to be in favor of a non magnetic origin of this noise. On the other hand at very low temperature (below 300 K-see pictures shown below), the application of a small magnetic field (i.e. 80 gauss) drives a very important change in a Lorentzian-like behavior appeared in our spectra. Although a direct correlation between noise and magnetoresistance can not be found out on our devices, a real discussion is open on the origin of this electrical fluctuation insight the Ferromagnetic state.