Invited Paper SP+AS+MI+NS+SS-FrM1
Direct Visualization of Magnetoelectric Domains in Hexagonal Manganites

Friday, October 23, 2015, 8:20 am, Room 212A

Multiferroics are materials with coexisting magnetic and ferroelectric orders, where the cross‐coupling between two ferroic orders can result in strong magnetoelectriceffects [1‐4]. Therefore, it is of both fundamental and technological interest to visualize cross‐coupled magnetoelectric domains and domain walls in multiferroics. Recently, intriguing topological defects with six interlocked structural antiphase and ferroelectric domains merging into a vortex core were revealed in multiferroic hexagonal REMnO₃ (R=rare earths) [5, 6]. Many emergent phenomena, such as enhanced conduction and unusual piezoelectric response, were observed in charged ferroelectric domain walls protected by these topological defects [7‐9]. More interestingly, alternating uncompensated magnetic moments were discovered at coupled structural antiphase and ferroelectric domain walls in hexagonal manganites using cryogenic magnetic force microscopy (MFM) [10], which demonstrates the cross‐coupling between ferroelectric and magnetic orders. Here we present the application of a magnetoelectric force microscopy (MeFM) technique that combines MFM with in situ modulating high electric fields. This new microscopy technique allows us to image the magnetoelectric response of the domain patterns in hexagonal manganites directly [11, 12]. We find that this response changes sign at each structural domain wall, a result that is corroborated by symmetry analysis and phenomenological modelling , and provides compelling evidence for a lattice-mediated magnetoelectric coupling. The direct visualization of magnetoelectric domains at mesoscopic scales opens up explorations of emergent phenomena in multifunctional materials with multiple coupled orders.

References

[1] N. A. Spaldin, and M. Fiebig, Science 309, 391 (2005).

[2] W. Eerenstein, N. D. Mathur, and J. F. Scott, Nature 442, 759 (2006).

[3] S‐W. Cheong, and M. Mostovoy, Nat. Mater. 6, 13 (2007).

[4] N. A. Spaldin, S.‐W. Cheong, and R. Ramesh, in Physics Today2010), pp. 38.

[5] T. Choi et al., Nature Materials 9, 253 (2010).

[6] T. Jungk et al., Appl. Phys. Lett. 97, 012904 (2010).

[7] E.B. Lochocki et al., Appl. Phys. Lett. 99, 232901 (2011).

[8] D. Meier et al., Nat. Mater. 11, 284 (2012).

[9] W. Wu et al., Phys. Rev. Lett. 108, 077203 (2012).

[10] Y. Geng et al., Nano Letters 12, 6055?6059 (2012).

[11] Y. Geng, and W. Wu, Rev. Sci. Instrum. 85, 053901 (2014).

[12] Y. Geng et al., Nat. Mater. 13, 163 (2014).