Conduction noise in La0.67Ca0.33MnO3 film

The temperature and frequency dependence of conduction noise in La0.67Ca0.33MnO3 film are reported. The film was prepared by a screen printing technique and had a metal–insulator transition temperature (Tp) and ferromagnetic transition temperature (TC) at 140 and 230 K, respectively. The magnetoresistance ratio (MRR) of the film at 1 kOe was found to be mainly due to grain boundaries. The observed voltage noise spectral density (Sv) shows 1/fα type behavior for all the temperatures ranging from 77 to 300 K. Sv shows an increase as the temperature is decreased below TC and reaches a peak value at Tp. The increase in Sv below TC is attributed to extra noise arising due to fluctuations in spin alignment in the ferromagnetic state. Application of a 1 kOe magnetic field reduces noise and the reduction in the noise is observed up to TC. A comparison of the temperature dependence of MRR and noise reduction ratio due to the magnetic field indicates that the magnetoresistance in the polycrystalline film of La0.67C...