NJIT Physics Department Seminar

March 1^st, 2010, Monday

Structural vortex in multiferroic hexagonal manganites

Prof. Weida Wu

Dept. of Physics, Rutgers Univ. - New Brunswick

(Condensed Matter Phyiscs, Host: Ahn)

Time: Noon-1 pm with 11:30 am tea time

Room: 407 Tiernan

Abstract: Hexagonal manganites (REMnO3) show a unique improper ferroelectricity induced by structrual trimerization. Extensive research on these systems has been carried due to its potential application in memory and the intriguing multiferroicity (coexistance of ferroelectricity and antiferromagnetism). However, the true ferroelectric domain structure and its relationship with structural domains have never been revealed. Using transmission electron microscopy (TEM) and conductive atomic force microscopy (c-AFM), we observed an intriguing conductive "cloverleaf" pattern of six domains emerging from one point, all distinctly characterized by polarization orientation and structural antiphase relationships in hexgonal manganites.[1] The cloverleaf defects are structural vortices where the phase angle goes successively through all six phases.[2] In addition, we discovered that the ferroelectric domain walls and structural antiphase boundaries are mutually locked. By correlating room temperature c-AFM with low temperature electrostatic force microscopy (EFM) images of the same sample region, we demonstrate that nanoscale electric conduction between a sharp tip and the surface is intrinsically modulated by the polarization of ferroelectric domains.[3] These fascinating results reveal the rich physics of the hexagonal system with a truly semiconducting bandgap where structural trimerization, ferroelectricity, magnetism and charge conduction are intricately coupled.

[1] T. Choi, et al, nat. mater., 9, 253-258 (2010)

[2] M. Mostovoy, nat. mater., 9, 188-190 (2010)

[3] W. Wu, et al, submitted to PRL, (2010)