Structures and Electromagnetic Properties of New Metal-Ordered Manganites; RBaMn_{2}O_{6} (R = Y and Rare Earth Elements)

TL;DR

This study synthesizes and analyzes new metal-ordered RBaMn_{2}O_{6} manganites, revealing distinct structural and electromagnetic behaviors across different rare earth elements, and proposing orbital ordering mechanisms linked to their unique layered structure.

Contribution

It introduces a comprehensive classification of RBaMn_{2}O_{6} manganites based on their properties and suggests a novel orbital ordering model related to their layered structure.

Findings

Three groups with distinct magnetic and charge-order behaviors.

High charge-order transition temperatures compared to disordered manganites.

Structural transitions occurring above charge-order temperatures in the third group.

Abstract

New metal-ordered manganites RBaMn_{2}O_{6} have been synthesized and investigated in the structures and electromagnetic properties. RBaMn_{2}O_{6} can be classified into three groups from the structural and electromagnetic properties. The first group (R = La, Pr and Nd) has a metallic ferromagnetic transition, followed by an A-type antiferromagnetic transition in PrBaMn_{2}O_{6}. The second group (R = Sm, Eu and Gd) exhibits a charge-order transition, followed by an antiferromagnetic long range ordering. The third group (R = Tb, Dy and Ho) shows successive three phase transitions, the structural, charge/orbital-order and magnetic transitions, as observed in YBaMn_{2}O_{6}. Comparing to the metal-disordered manganites (R^{3+}_{0.5}A^{2+}_{0.5})MnO_{3}, two remarkable features can be recognized in RBaMn_{2}O_{6}; (1) relatively high charge-order transition temperature and (2) the presence of structural transition above the charge-order temperature in the third group. We propose a possible orbital ordering at the structural transition, that is a possible freezing of the orbital, charge and spin degrees of freedom at the independent temperatures in the third group. These features are closely related to the peculiar structure that the MnO_{2} square-lattice is sandwiched by the rock-salt layers of two kinds, RO and BaO with extremely different lattice-sizes.