Momentum-resolved observations of the phonon instability driving geometric improper ferroelectricity in yttrium manganite.


Magnetoelectrics offer tantalizing opportunities for devices coupling ferroelectricity and magnetism but remain difficult to realize. Breakthrough strategies could circumvent the mutually exclusive origins of magnetism and ferroelectricity by exploiting the interaction of multiple phonon modes in geometric improper and hybrid improper ferroelectrics. Yet, the proposed instability of a zone-boundary phonon mode, driving the emergence of ferroelectricity via coupling to a polar mode, remains to be directly observed. Here, we provide previously missing evidence for this scenario in the archetypal improper ferroelectric, yttrium manganite, through comprehensive scattering measurements of the atomic structure and phonons, supported with first-principles simulations. Our experiments and theoretical modeling resolve the origin of the unusual temperature dependence of the polarization and rule out a reported double-step ferroelectric transition. These results emphasize the critical role of phonon anharmonicity in rationalizing lattice instabilities in improper ferroelectrics and show that including these effects in simulations could facilitate the design of magnetoelectrics.






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Publication Info

Bansal, Dipanshu, Jennifer L Niedziela, Ryan Sinclair, V Ovidiu Garlea, Douglas L Abernathy, Songxue Chi, Yang Ren, Haidong Zhou, et al. (2018). Momentum-resolved observations of the phonon instability driving geometric improper ferroelectricity in yttrium manganite. Nature communications, 9(1). 10.1038/s41467-017-02309-2 Retrieved from

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Olivier Delaire

Associate Professor of the Thomas Lord Department of Mechanical Engineering and Materials Science

The Delaire group investigates atomistic transport processes of energy and charge, and thermodynamics in energy materials. We use a combined experimental and computational approach to understand and control microscopic energy transport for the design of next-generation materials, in particular for sustainable energy applications. Current materials of interest include superionic conductors, photovoltaics, thermoelectrics, ferroelectrics/multiferroics, and metal-insulator transitions. Our group's studies provide fundamental insights into  atomic dynamics and elementary excitations in condensed-matter systems (phonons, electrons, spins), their couplings and their effects on macroscopic properties. We probe the microscopic underpinnings of transport and thermodynamics properties by integrating neutron and x-ray scattering, optical spectroscopy, and thermal characterization, together with quantum-mechanical computer simulations.

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