Unusual magnetodielectric effects in La2CuMnO6 induced by a dynamic crossover in dielectric relaxation at TC

Abstract

A series of fixed frequency dielectric measurements shows dielectric relaxation in La2CuMnO6, with a dynamic (Arrhenius to Arrhenius) crossover at TC. The external magnetic field alters the relaxation parameters in the vicinity of crossover and induces an unusual trend in the magnetodielectric coupling around TC. A large magnetodielectric coupling of 55% (at 68 K, 4 kHz) and 61% (at 105 K, 285.8 kHz) under a small magnetic field of 5 kOe is discovered. Presence of ferromagnetic short-range correlations above TC and a sign reversal of magnetoresistance around TC are observed. Specific heat analysis revealed the presence of ferromagnetic, variable range hopping active charge localized state. The presence of ferromagnetic short-range correlations and the influence of a core-grain dominated magnetoresistance on the Maxwell-Wagner interfacial polarization are responsible for the observed large magnetodielectric effect. Both the magnetic ordering and external magnetic field control the electric dipole relaxation in the material.