Magnetic and electron transport properties of the rare-earth cobaltates, La0.7-xLnxCa0.3CoO3 (Ln = Pr, Nd, Gd and Dy) : A case of phase separation

TL;DR

This study investigates the magnetic and electrical properties of La0.7-xLnxCa0.3CoO3 cobaltates, revealing phase separation and cluster size effects on magnetism and conductivity, with implications for understanding complex magnetic behaviors in these materials.

Contribution

It provides a detailed analysis of phase separation and magnetic cluster evolution in La0.7-xLnxCa0.3CoO3 cobaltates, linking structural changes to magnetic and electrical properties.

Findings

Large ferromagnetic clusters near x=0.0 with high Tc

Electrical resistivity increases with x and shows a critical transition

Phase separation involves coexistence of large hole-rich and small hole-poor clusters

Abstract

Magnetic and electrical properties of four series of rare earth cobaltates of the formula La0.7-xLnxCa0.3CoO3 with Ln = Pr, Nd, Gd and Dy have been investigated. Compositions close to x = 0.0 contain large ferromagnetic clusters or domains, and show Brillouin-like behaviour of the field-cooled DC magnetization data with fairly high ferromagnetic Tc values, besides low electrical resistivities with near-zero temperature coefficients. The zero-field-cooled data generally show a non-monotonic behaviour with a peak at a temperatures slightly lower than Tc. The near x = 0.0 compositions show a prominent peak corresponding to the Tc in the AC-susceptibility data. The ferromagnetic Tc varies linearly with x or the average radius of the A-site cations, (rA). With increase in x or decrease in (rA), the magnetization value at any given temperature decreases markedly and the AC-susceptibility measurements show a prominent transition arising from small magnetic clusters with some characteristics of a spin-glass. Electrical resistivity increases with increase in x, showed a significant increase around a critical value of x or (rA), at which composition the small clusters also begin to dominate. These properties can be understood in terms of a phase separation scenario wherein large magnetic clusters give way to smaller ones with increase in x, with both types of clusters being present in certain compositions. The changes in magnetic and electrical properties occur parallely since the large ferromagnetic clusters are hole-rich and the small clusters are hole-poor. Variable-range hopping seems to occur at low temperatures in these cobaltates.