En-Pei Liu | Searcharxiv

arXiv2025

The magnetic structure of polar $G$-type charge and orbital ordered Hg-quadruple manganite perovskites

The magnetic structure of the novel Hg$_{0.7}$Na$_{0.3}$Mn$_3$Mn$_4$O$_{12}$, a quadruple manganite perovskite that exhibits a unique $G$-type charge and orbital ordered state distinct to other $A^{2+}$Mn$_3$Mn$_4$O$_{12}$ equivalents ($A$ $=$ Ca, Sr, Cd, Pb), has been solved using powder neutron diffraction and symmetry-motivated analysis. A $G$-type-like antiferromagnetic (AFM) ordering of Mn on the $A'$ sites and a `up--up--down--down' AFM moment configuration of Mn spins on the $B$ sites is found to occur. The mechanism for the onset and stabilization of $B$ site `up--up--down--down' AFM order is explored in terms of coupling between structural and magnetic distortions. The results presented here provide evidence of the exotic charge, orbital, electronic and magnetic orderings that quadruple manganite perovskites demonstrate, and further highlighting the distinct chemistry that Hg$^{2+}$ plays in stabilizing novel states compared to other divalent $A$-site cation equivalents.

cond-mat.str-el↗

arXiv2024

Intrinsic electronic phase separation and competition between $G$-type, $C$-type and $CE$-type charge and orbital ordering modes in Hg$_{1-x}$Na$_x$Mn$_3$Mn$_4$O$_{12}$

The novel series of hole-doped quadruple manganite perovskites Hg$_{1-x}$Na$_x$Mn$_3$Mn$_4$O$_{12}$ (HNMO) has been synthesized and its charge and orbital order behavior investigated through high-resolution synchrotron powder x-ray diffraction techniques. Through careful Rietveld refinements of structural models $via$ symmetry-motivated approaches, we show that the ground state of HNMO compositions adopts a polar $G$-type charge and orbital ordered state, which is rare in manganite perovskites, and is robust as a sole phase up to a critical doping level. Upon this critical doping, coincident with that in which colossal magnetoresistance (CMR) is maximal in canonical manganite perovskites, electronic phase separation occurs between $G$-type and orbital order with charge disorder-type states. The latter state has recently been identified in Ca$_{1-x}$Na$_x$Mn$_3$Mn$_4$O$_{12}$ perovskites, and proposed to be the competing insulating state from which CMR phenomena emerges. We show the mechanism for the formation of the $G$-type state is due to charge transfer processes which may occur through a coupling of distortions involving structural and charge and orbital degrees of freedom, ultimately driving the polar ground state through an improper-like ferroelectric polarization mechanism. These results will act as an important recipe for designing novel ferroelectric-active materials, in addition to expanding the richness of charge and orbital ordered states in manganite perovskites.

cond-mat.str-el↗