La0.67(Ca0.24Sr0.09)MnO3:xAg2O (0 ≤ x ≤ 0.25) composites with improved room–temperature TCR and MR for advanced uncooling infrared bolometers and magnetic sensors

Abstract

In this research, high–density La0.67(Ca0.24Sr0.09)MnO3:xAg2O (LCSMO: xAg2O, x = 0, 0.05, 0.1. 0.15, 0.2, and 0.25) composites were successfully fabricated through the conventional sol-gel method. Scanning electron microscopy (SEM), X–ray photoelectron spectroscopy (XPS) and XRD data confirmed presence of silver at A sites (La3+/Ca2+/Sr2+) as Ag+ and segregates at grain boundaries (GBs) to form metallic silver. The electrical properties greatly improved by adding Ag2O. Significant enhancements in peak temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at room–temperature (300 K) were observed for LCSMO:xAg2O composites. The peak TCR increased from 3.7% K−1 (299.3 K, for x = 0) to 14.8% K−1 (301.0 K, for x = 0.2), and MR rose from 16.9% (303.0 K, for x = 0) to 34.1% (300.6 K, for x = 0.2). These improvements in peak TCR were attributed to increased grain size and formation of metallic silver at GBs or within the composites. Moreover, peak MR was higher in Ag2O doped composites, which was mainly due to large spin polarization effect and strong coupling ferromagnetic domains under external magnetic field. Overall, the large room-temperature TCR and MR values of LCSMO:0.2Ag2O composites look promising for future advanced uncooling infrared bolometers and magnetic sensors.