Low Frequency Noise in High T_C Ferromagnetic La_2/3Sr_1/3MnO₃ 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 La_{1 − 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.

Keywords:

• Manganites
• giant magnetoresistance
• noise
• thin films

Acknowledgments

This work was sponsored partly by the French Ministry of Research within the “ACI Nanosciences” program and by the “Centre National de la Recherche Scientifique” within the “ATIP program”. We thank very much Ch. Simon for the fruitful discussions and magnetization measurements, and S. Eimer and S. Lebargy for the technical help.