Ferromagnetic clusters in the Brownmillerite bilayered compounds Ca_2.5-xLa_xSr_0.5GaMn₂O₈: an approach to achieve layered spintronics materials

Abstract

We report the effect of La substitution on the magnetic and magnetotransport properties of Brownmillerite-like bilayered compounds Ca_2.5-xLa_xSr_0.5GaMn₂O₈ (x=0x=0, 0.05, 0.075, and 0.1) by using dc magnetization, resistivity, and magnetoresistance techniques. The Rietveld analysis of the room temperature x-ray diffraction patterns confirms no observable change in average crystal structure with the La substitution. Both magnetic and magnetotransport properties are found to be very sensitive to the La substitution. Interestingly, the La-substituted compounds show ferromagneticlike behavior (due to the occurrence of a double exchange mechanism), whereas the parent compound is an antiferromagnet (T_N∼150 K)(T_N∼150 K). All compounds show an insulating behavior in the measured temperature range of 100–300 K, with an overall decrease in the resistivity with the substitution. A higher value of magnetoresistance has been successfully achieved by the La substitution. We have proposed an electronic phase separation model, considering the formation of ferromagnetic clusters in the antiferromagnetic matrix, to interpret the observed magnetization and magnetotransport results for the La-substituted samples. The present study demonstrates an approach to achieve new functional materials, based on naturally occurring layered system like Ca_2.5-xLa_xSr_0.5GaMn₂O₈, for possible spintronics applications.