Abstract
It is of great interest to design and make materials in which ferroelectric polarisation is coupled to other order parameters such as lattice, magnetic and electronic instabilities. Such materials will be invaluable in next-generation data storage devices. Recently, remarkable progress has been made in understanding improper ferroelectric coupling mechanisms that arise from lattice and magnetic instabilities. However, although theoretically predicted, a compact lattice coupling between electronic and ferroelectric (polar) instabilities has yet to be realised. Here we report detailed crystallographic studies of a novel perovskite Hg$^{\textbf{A}}$Mn$^{\textbf{A'}}_{3}$Mn$^{\textbf{B}}_{4}$O$_{12}$ that is found to exhibit a polar ground state on account of such couplings that arise from charge and orbital ordering on both the A' and B-sites, which are themselves driven by a highly unusual Mn$^{A'}$-Mn$^B$ inter-site charge transfer. The inherent coupling of polar, charge, orbital and hence magnetic degrees of freedom, make this a system of great fundamental interest, and demonstrating ferroelectric switching in this and a host of recently reported hybrid improper ferroelectrics remains a substantial challenge.
Highlights
Considerable efforts have been made in the search for novel multiferroics, and as such materials will undoubtedly find utility in future solid-state storage devices, driving both capacity and data access speeds ever higher
Remarkable progress has been made in understanding improper ferroelectric coupling mechanisms that arise from lattice and magnetic instabilities
In the field of improper ferroelectrics, remarkable progress has been made in understanding the coupling mechanisms that arise from lattice and magnetic instabilities [8,9,10]
Summary
Considerable efforts have been made in the search for novel multiferroics, and as such materials will undoubtedly find utility in future solid-state storage devices, driving both capacity and data access speeds ever higher In these materials, it is essential to investigate the coupling between ferroelectric polarization and other order parameters [1,2,3,4,5]. One of the most notable examples is CaMn7O12, which has a so-called 134-perovskite AA 3B4O12 structure (top panel Fig. 1 for aristotype) This example was believed to represent the largest magnetically induced polarization reported to date [16,17], more recent findings dispute this [18]. There is a charge transfer of one electron per unit cell from B- to A -site on going from R3 ̄ to P nn, which acts to remove the orbital disordered state and facilitates the double charge order on the A - and B-site
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
