Structural and magnetic properties of the new cobaltate series (BaSr)4-xLa2xCo4O15

TL;DR

This study explores the structural and magnetic characteristics of a new cobaltate series, revealing complex magnetic interactions and spin-glass behavior influenced by La doping, with implications for understanding charge distribution and magnetic frustration.

Contribution

It introduces a new cobaltate series with detailed structural and magnetic analysis, highlighting the effects of La substitution on charge distribution and magnetic properties.

Findings

All compositions exhibit a three-dimensional Heisenberg spin-glass state.

La doping reduces charge randomness and slows spin dynamics.

Competing magnetic interactions lead to complex magnetic behavior.

Abstract

We report the structural and magnetic properties of a new class of cobaltates with the chemical formula (BaSr)4-xLa2xCo4O15 (x = 0, 0.5 and 1). These compounds crystallize in a hexagonal structure in which cobalt ions are distributed among two distinct crystallographic sites with different oxygen coordination. Three Co-O tetrahedra and one octahedron are linked by shared oxygen atoms to form Co4O15 clusters, which are packed together into a honeycomb-like network. Partial substitution of Sr and/or Ba atoms by La allows one to adjust the degree of Co valence mixing, but all compositions remain subject to a random distribution of charge. Magnetic susceptibility together with neutron scattering measurements reveal that all studied specimens are characterized by competing ferro- and antiferro-magnetic exchange interactions that give rise to a three dimensional Heisenberg spin-glass state. Neutron spectroscopy shows a clear trend of slowing down of spin-dynamics upon increasing La concentration, suggesting a reduction in charge randomness in the doped samples.