Enhanced Magnetotransport Properties of Ag-doped La_0.7Ca_0.3-xAg_xMnO₃ Polycrystalline Ceramics

The present report focuses on the successful synthesis of La_0.7Ca_0.3−xAg_xMnO₃ (x = 0, 0.10, 0.15, 0.20, and 0.30) polycrystalline manganite samples through a soft chemical polymeric precursor route and subsequent impact of Ag doping and grain size on their magnetotransport features. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses reveal that Ag doping leads to a phase transformation from the orthorhombic phase to the rhombohedral phase (for x ≥ 15%). Furthermore, it shows that the insulator–metal transition temperature (T_IM) and paramagnetic–ferromagnetic (PM-FM) transition temperature (T_C) increase with Ag doping concentration and also with the sintering temperature. The prime factors leading to the enhancement with Ag doping are the well-known oxygenation effect by metallic Ag, which helps to improve the transport properties of La_1−xCa_xMnO₃ (LCMO) manganite, and the increase in the tolerance factor (τ), which in turn leads to the Mn-O-Mn bond angle and the structural disorder near the grain boundaries that weaken the double exchange. The room temperature magnetoresistance values are found to be higher for Ag-doped LCMO samples than for the pristine LCMO. The enhanced ferromagnetic ordering temperature along with low-field magnetoresistance (LFMR) of the as-synthesized Ag-doped LCMO polycrystalline ceramic indicate its potential for device fabrication.