The search for multiferroic materials, in which a magnetic polarization may be induced by the application of an external electric field, or an electric polarization may be induced by the application of an external magnetic field, has attracted considerable attention, both from the point of view of fundamental scientific challenge as well as the potential technological applications in spintronics and magnetic data storage devices.1,2 Quite recently, a giant improper ferroelectric polarization of magnitude 2870 ?Cm-2, has been observed in a mixed-valent manganate, CaMn7O12.3 However, the underlying phenomenon governing such a large ferroelectric polarization is still under debate. Initially, the improper ferroelectric polarization was explained in terms of the Dzyaloshinskii-Moriya interaction, caused by the symmetric exchange striction due to the canting of the Mn4+ spin.4 Later on, magneto-orbital helices were identified as a route to the coupling of magnetism and ferroelectricity in CaMn7O12. Using first principle methods, we confirm the experimental observations5that in order to stabilize the chiral magnetic structure, orbital ordering is crucial, and the presence of a global structural rotation enables the coupling between this polarization and magnetic helicity, which governs the multiferroicity. The present study provides insights that clarify in detail the phenomenological coupling mechanism, the understanding of which is essential to the design of new materials with high-temperature enhanced magneto-electric effects.1. S.-W. Cheong and M. Mostovoy, Nature Mater. 6, 13 (2007). 2. R. Ramesh and N.A. Spaldin, Nature Mater. 6, 21 (2007). 3. R. D. Johnson, L. C. Chapon, D. D. Khalyavin, P. Manuel, P. G. Radaelli, and C. Martin, Phys. Rev. Lett. 108, 067201 (2012). 4. X. Z. Lu, M.-H. Whangbo, Shuai Dong, X. G. Gong, and H. J. Xiang, Phys. Rev. Lett. 108, 187204 (2012) 5. N.J. Perks, R.D. Johnson, C. Martin, L.C. Chapon and P.G. Radaelli, Nature Comm. 3, 1277 (2012).

Origin of giant improper ferroelectric polarization in CaMn<sub>7</sub>O<sub>12</sub>: A first principles perspective

246th National Meeting (2013)

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Origin of giant improper ferroelectric polarization in CaMn7O12: A first principles perspective

Origin of giant improper ferroelectric polarization in CaMn₇O₁₂: A first principles perspective