High Tcr and Mr in Magnetic Fields Enabled Polycrystalline La0.72ca0.28mn0.98cr0.02o3 for Efficient and Stable Electromagnetic Device

To obtain comprehensive materials with both high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at low magnetic fields, polycrystalline La0.72Ca0.28Mn1− x Cr x O3 (x = 0, 0.02, 0.04, 0.06) ceramics were prepared herein by the sol–gel method. The electronic configuration of Cr3+ ions is similar to that of Mn4+ ions; therefore, successive substitution of Cr increases the electrical resistivity and decreases the metal–insulator transition temperature of ceramics, even yielding hump-like feature for Cr-rich (x = 0.06) samples. The best TCR (28.50%·K-1) and MR (72.37%) values were obtained simultaneously at Cr dopant content of 0.02 (La0.72Ca0.28Mn0.98Cr0.02O3). The strong response of the material to temperature and magnetic field was caused by the minimal symmetry of the orthorhombic structure and the most robust Jahn–Teller distortion. With increasing Cr content, Mn3+/Mn4+ or Mn3+/Cr3+ double exchange was diluted, and Cr3+/Cr3+ or Cr3+/Mn4+ superexchange was promoted. However, the internal competition effect was not conducive to the improvement in material properties