Comparison of pressure, magnetic-field, and excess manganese effects on transport properties of film and bulk ceramic La–Ca manganites

Abstract

The pressure, magnetic field and excess manganese effects on transport and magnetoresistance effect (MRE) have been studied in both the epitaxial films and bulk ceramics of manganites (La 0.7 Ca 0.3) 1-x Mn 1+x O 3-y (x = 0-0.2). A comparison of electrical behavior in both kinds of samples of similar composition at hydrostatic pressures of up to 1.8 GPa and in a magnetic fields of up to 8 kOe has been performed. The pressure and magnetic field effects are shown to increase with increasing manganese content. Experimental data show that the pressure and magnetic field effects on temperatures of both metal-insulator transition (T MD) and MRE peak (T MR) are considerably stronger in the films than in ceramics. The hydrostatic pressure increases T MD and T MR. Magnetoresistance effect for both types of samples was shown to be favored by the pressure and magnetic field in an opposite way. A direct correlation is established between T MD and conductivity bandwidth as well as between MRE and concentration of charge carriers at applied pressure. The differences in the values of pressure effect on resistance, MRE and T MD temperature in the films and ceramics are connected with both granular structure of ceramics and the oxygen nonstoichiometry in ceramic and film samples of the same content as well as with the film strain induced by lattice mismatch between the film and the substrate. The origin of pressure-magnetic field effects is analyzed in the framework of double exchange interaction and small polaron hopping, and variable range hopping models.

Impact of Alkali Ions Codoping on Magnetic Properties of La0.9A0.1Mn0.9Co0.1O3 (A: Li, K, Na) Powders and Ceramics

“…The observed reflection is attributed to h-BN material integrated into tablets during the pressure procedure, which does not affect the crystal structure and the magnetic properties. In the case of ceramics, the applied pressure leads to a decrease in the unit cell volume, which has a significant impact on the magnetic properties of the ceramics as compared to the starting powders [35]. As the XRD measurements were performed in the reflection mode, the ceramics are small and, in some cases, they do not have parallel surfaces, the XRD patterns at high 2Θ degrees become noisy and the baseline rises.…”