Magnetotransport of La0.70Ca0.3-xSrxMnO3(Ag): A potential room temperature bolometer and magnetic sensor

Here we report the optimized magnetotransport properties of polycrystalline La0.70Ca0.3-xSrxMnO3 and their composites with Ag. The optimization was carried out by varying the Sr and Ag contents simultaneously to achieve large temperature coefficient of resistance (TCR) as well as low field magnetoresistance (MR) at room temperature. Sharpest paramagnetic (PM)-ferromagnetic (FM) and insulator-metal (IM) transition is observed in the vicinity of the room temperature (T-C approximate to 300 K approximate to T-IM) for the composition La0.70Ca0.20Sr0.10MnO3:Ag-0.20. Partial substitution of larger Sr2+ ions at the Ca2+ ions sites controls the magnitude of the FM and IM transition temperatures, while the Ag induces the desired sharpness in these transitions. For the optimized composition, maximum TCR and MR are tuned to room temperature (300 K) with the former being as high as 9% and the later being similar to 20% and similar to 30% at 5 and 10 kOe magnetic fields respectively. Such sharp single peak (TCR similar to 9%) at room temperature can be used for the bolometric and infrared detector applications. The achievement of large TCR and low field MR at T similar to 300 K in polycrystalline samples is encouraging and we believe that further improvements can be achieved in thin films which by virtue of their low conduction noise are more suitable for device applications. (C) 2010 American Institute of Physics. [doi:10.1063/1.3365412]