Deterministic control of ferroelastic switching in multiferroic materials
N. Balke1, S. Choudhury2, S. Jesse1, M. Huijben3,4, Y.H. Chu3,5, A.P. Baddorf1, L.Q. Chen2, R. Ramesh3 and S.V. Kalinin1
We have demonstrated a new technique to guide the ferroelastic switching process in bismuth ferrite, one of the most popular magnetoelectric materials envisioned for memory and logic devices. Using the symmetry breaking of a moving SPM probe, we can selectively write domains which are otherwise thermodynamically equivalent but differ in magnetization and strain. Remarkably, this control of polarization switching allows for the creation of the first unambiguous ferroelectric closure domain pattern, the precursor to the long-sought ferroelectric vortex state.
|Switching in (100) rhombohedral ferroelectrics can proceed in 4 equivalent states, which cannot be selected without broken symmetry.||Phase field modeling allows the deterministic switching mechanisms to be deciphered. Tip motion can be used to stabilize the preferred polarization state (color) at an existing domain wall (left) or in a uniform domain (right).|
Realization of the next generation of magnetoelectric, strain-coupled, and domain-wall based devices necessitates the control of polarization switching in multiferroics with multiple possible polarization directions. In rhombohedral ferroelectrics, application of an electric field in the pseudocubic (001) direction can lead to 180° ferroelectric switching or to 71° and 109° ferroelastic switching. While the electrostatic energy gain is equivalent, the magnetic and strain states and domain wall properties of the final structures are quite different. In this research we illustrate the deterministic control of ferroelastic switching in these materials using symmetry breaking caused by a moving scanning probe. The fabrication of predefined domain patterns is demonstrated through the creation of artificial ferroelectric closure domains which are believed to be the precursors to vortex domains (see Figure 1). This discovery enables a reliable pathway for the design and creation of domain engineered magnetoelectric, domain-wall based, and strain coupled devices.
More broadly, these results illustrate that mechanisms of phase transitions leading to equivalent final states can be preferentially selected by local stimulus. It was traditionally believed that only biological systems can undergo multiple mechanisms with comparable energies, while phase transitions in inorganic materials were limited to those between only two states. Here, we demonstrate that deterministic selection mechanisms can be understood and controlled at nanometer scales.
Switching in (100) rhombohedral ferroelectrics can proceed in 4 equivalent states, which cannot be selected without broken symmetry.
Phase field modeling allows the deterministic switching mechanisms to be deciphered. Tip motion can be used to stabilize the preferred polarization state (color) at an existing domain wall (left) or in a uniform domain (right).
|By controlling the symmetry with the tip motion, the writing of a closure domain pattern formed by vortex and antivortex states is now possible.|
This work was published online in Nature Nanotechnology Vol. 4, 2009, 868-875 This research at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy (NB, SJ, APB) and ORNL LDRD program (SVK, LQC). SC and LQC at Penn State acknowledge the financial support of NSF under DMR-0213623, DMR-0507146. NB acknowledges Alexander von Humboldt foundation. The theory work at Pennsylvania State University is also supported by the Department of Energy Basic Sciences under DE-FG02-07ER46417 (L.Q.C.). Y.H.C. would like to acknowledge the support of the National Science Council, Republic of China, under contract No. NSC 98-2119-M-009-019. N.B. acknowledges support from the Alexander von Humboldt Foundation