Fast protector against EMP using electrical field induced resistance change in La/sub 0.67/Ca/sub 0.33/MnO/sub 3/ thin films

摘要

Summary form only given. The La/sub 0.67/Ca/sub 0.33/MnO/sub 3/ thin films exhibiting colossal magnetoresistance (CMR) phenomenon were investigated using nanosecond duration electric and magnetic pulses. The films used for the investigation were prepared by pulsed laser deposition technique. MgO served as a substrate. The deposition was performed under oxygen pressure 20-25 Pa using ceramic target of La/sub 0.67/Ca/sub 0.33/MnO/sub 3/ composition. So fabricated films had phase transition temperature (T/sub m/) ranging from 125 K to 135 K. The specific resistance of the film depended on its thickness and decreased about eight times when thickness of these films increased from 0.05 to 0. 12 /spl mu/m. The investigation of electric field (up to 30 kV/cm) induced resistance change was carried out using electrical pulses having 1 ns rise time and 100 ns duration. The magnetic field pulse had a sinusoidal wave form with 0.3 T amplitude and 40 ns duration. Both electric and magnetic field in this case significantly reduces the resistance of the film and shifts the peak in resistance-vs-temperature dependence to higher temperatures region. The results are discussed using model based on fast spin and charge systems response to magnetic and electric field action on the manganite. It was concluded that electric field induced change of La/sub 0.67/Ca/sub 0.33/MnO/sub 3/ thin film resistance can be used for fast 50 Ohm impedance high frequency transmission lines protection against short rise time fault current pulses.