Effect of La-site substitution on the magnetoelectric transport properties of La0.7Ca0.3MnO3 polycrystalline ceramics

Abstract

A series of La0.64RE0.06Ca0.3MnO3 (RE = Nd, Eu, Gd, Dy, and Er) polycrystalline ceramics were prepared by the sol-gel method. The effects of the substitution element types on the structure, electrical transport properties and magnetic properties of the polycrystalline ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and other tests. The results show that as the ionic radius of the substitute elements decreases, the cell volume decreases, the grain size increases, the peak resistivity increases exponentially, the metal insulator transition temperature decreases linearly, the temperature coefficient of resistance (TCR) shows a trend of first decreasing and then increasing, the peak TCR of these samples reaches 43.4%, and the magnetoresistance (MR) shows a trend of gradually increasing, reaching 92.4% at a 1 T magnetic field. Based on small polaron hopping（SPH） model, variable range hopping（VRH）model and the phase separation mechanism, fitting the resistivity temperature curves of polycrystalline ceramics shows that elemental doping changes the electrical transport properties mainly by influencing the crystal structure and thus the activation energy Eα. When the radius of the doped element ions is large, the peak TCR is close to dρ/dTmax, so the main influence is the paramagnetic (PM) phase resistance. When the radius of the dopant element ions is small, the peak TCR is far from dρ/dTmax, so the main influence is the ferromagnetic (FM) phase resistance.