Multiferroic properties of nanocrystalline BaTiO3

摘要

Some of the Multiferroics H. Schmid, Ferroelectrics 162 (1994) 317 form a rare class of materials that exhibit magneto electric coupling arising from the coexistence of ferromagnetism and ferroelectricity,with potential for many technological applications J.F. Scott, Nat. Mater. 6 (2007) 256; N.A. Spaldin,M. Fiebig, Science 309 (2005) 391. Over the last decade, an active research on multiferroics has resultedin the identification of a few routes that lead to multiferroicity in bulk materials C. Ederer, N.A. Spaldin,Nat. Mater. 3 (2004) 849; D.V. Efremov, J. van den Brink, D.I. Khomskii, Nat. Mater. 3 (2004) 853; N. Hur,S. Park, P.A. Sharma, J.S. Ahn, S. Guha, S.W. Cheong, Nature 429 (2004) 392. While ferroelectricity in a classic ferroelectric such as BaTiO3 is expected to diminish with the reducing particle size, C.H. Ahn,K.M. Rabe, J.M. Triscone, Science 303 (2004) 488; J. Junquera, P. Ghosez, Nature 422 (2003) 506 ferromagnetism cannot occur in its bulk form N.A. Hill, J. Phys. Chem. B 104 (2000) 6694. Here, we usea combination of experiment and first-principles simulations to demonstrate that multiferroic nature emerges in intermediate size nanocrystalline BaTiO3, ferromagnetism arising from the oxygen vacancies at the surface and ferroelectricity from the core. A strong coupling between a surface polar phonon and spin is shown to result in a magnetocapacitance effect observed at room temperature, which can open up possibilities of new electro magneto-mechanical devices at the nano-scale.