Magnetoimpedance spectroscopy of phase-separated La 0.5 Ca 0.5 MnO 3 polycrystalline manganites.

Magnetoimpedance spectroscopy was carried out on phase-separated La0.5Ca0.5MnO3 polycrystalline manganites. The La0.5Ca0.5MnO3 powder was synthesized following an adapted sol-gel route. Structural and magnetic data showed the signs of phase coexistence of ferromagnetic (FM) Pnma and charge-ordered antiferromagnetic (CO-AFM) P2(1)/m phases. Magnetization vs. temperature (M vs. T) measurements revealed several magnetic transitions from the high temperature paramagnetic (PM) to an FM phase upon cooling (PM-FM) at approximate to 240 K, FM-AFM (approximate to 170 K) and AFM-FM (approximate to 100 K). Magnetic field (H)-dependent impedance spectroscopy data were collected from sintered pellets and fitted with an equivalent circuit model to separately analyze the different dielectric contributions from the grain boundary (GB) and the grain interior bulk areas. This allowed separating the GB and bulk magnetoresistance (MR), which was shown to amount to a maximum of approximate to 80% for both GB and bulk at H = 10 T near the metal-insulator transition (MIT) at approximate to 100 K. The GB resistance was found to be larger than the bulk resistance by a factor of approximate to 3, which implies that the direct current (DC) resistance and DC MR are dominated by contributions from the GBs. The magnetocapacitance (MC) effects detected were all found to be small below approximate to 3%, including in the presence of a CO phase.