Magnetic and Electrical Transport Properties of Er2O3-Doped La0.7Ca0.3MnO3 Composites

The (La_0.7Ca_0.3MnO₃)_1?x /(Er₂O₃) _x composites with x=0, 1, 2, 3, 4, 7, 9, 15, 17, and 20% were prepared by a solid state reaction process. The magnetic and electrical transport properties of the composites were investigated. The X-ray diffraction (XRD), scanning electronic microscopy (SEM), and the calculation of lattice parameters of La_0.7Ca_0.3MnO₃ (LCMO) indicated that there is no reaction between La_0.7Ca_0.3MnO₃ and Er₂O₃; especially, compared with pure LCMO, a new metal-insulator transition temperature (T _P2) was observed at a lower temperature in some composites with x=1,2,3,4, and 7%, which may result from the existence of a new phase related to Er₂O₃ dopant at grain boundaries or surfaces of LCMO grains. An enhancement of low field magnetoresistance (LFMR) is obtained at temperature below 130 K for the composites with higher Er₂O₃ content, but the intrinsic CMR at T _P1 decreased monotonously with increasing Er₂O₃ content. The increased LFMR results from the spin-dependent scattering and spin-polarized tunneling at the grain boundaries and the decreased intrinsic CMR due to the Double Exchange (DE) interaction between Mn³⁺ and Mn⁴⁺ ions.