Comparison of the Magnetic, Conduction, and Magnetotransport Behaviors of Ba²⁺‐ and Al³⁺‐Doped La_0.67Ca_0.33MnO₃

Abstract

A modified Pechini method was used to prepare undoped and doped La 0.67 Ca 0.33 MnO 3 (LCMO) with homogeneous compositions and uniform fine powders. The variations of the lattice parameters and cell volumes of doped LCMO are attributed to the effect of ionic size and the creation of the oxygen vacancy. The effect of Ba 21 on the magnetic and conduction properties of LCMO is mainly related to the enhancement of the Mn 31 -O-Mn 41 bond angle. The occupation of Al ions in Mn sites and the creation of the oxygen vacancies lead to an increase of the resistivity and a decrease of T c and M s . The variable-range hopping model with p 5 1/4 and q 0 independent of temperature was found to be the best fit for undoped and doped LCMO, shown in Fig. 4. It is suggested that T 0 is mainly the measure of the extent of the disorder. For Al 31 -doped LCMO, the small-polaron mechanism was found to be dominant in the temperature range from 300 to 350 K, and the evaluated values of the activation energy are about 0.22 eV and independent of the Al concentration. Low-field magnetoresistance (LFMR) was found to be enhanced by Ba doping but diminished by Al doping. The segregation of Al ions to the grain-boundary region may play a significant role in the intent to form a one-slope field-dependent MR response. The mechanisms of MR response of doped LCMO were suggested. J ournal