Hysteretic "Magnetic-Transport-Structural" Transition in "114" Cobaltites: Size Mismatch Effect

TL;DR

This study investigates how size mismatch and cationic disorder at lanthanide sites influence the magnetic, transport, and structural transitions in

Contribution

It is the first to demonstrate the effect of size mismatch on the hysteretic transition in a triangular lattice cobaltite system.

Findings

Increasing <rLn> raises transition temperature TS.

Size mismatch {}2 decreases TS.

Cationic mismatch alters the transition from sharp first order to mixed order.

Abstract

The triple "magnetic-transport-structural" transition versus temperature in three series of "114" cobaltites - Y1-xYbxBaCo4O7, Y1-xCaxBaCo4O7 and Yb1-xCaxBaCo4O7 - has been studied using magnetic, transport and differential scanning calorimetric measurements. The effect of the size mismatch {\sigma}2, due to cationic disordering at the Ln sites upon such a transition is shown for the first time in a triangular lattice. We show that increasing <rLn> has an effect of increasing TS dramatically, while the size mismatch {\sigma}2 at the Ln sites decreases TS substantially. Moreover, the cationic mismatch at the Ln sites modifies the nature of the hysteretic transition by turning the sharp first order transition seen in the undoped samples into an intermix of first and second order transitions. These results are discussed on the basis of the particular nature of the high temperature form which exhibits a hexagonal close packed structure (space group: P63mc) with respect to the low temperature orthorhombic form (space group: Pbn21), the latter corresponding to a distortion of the former due to a puckering of the kagom\'e layers.