Simulations explore the landscape of electric order in bismuth ferrite nanoislands

In hard drives and other storage media, magnetic order stores and protects data in magnetic domains. Similar domains can emerge in materials with electric order, in which neighboring electric polarization vectors line up together. However, building real devices with stable configurations of electric domains is challenging due to the effects of bound charges and device geometry on the free energy landscape. There also exist technical difficulties in toggling and maintaining electric order configurations in materials.

A recent paper from Peng et al. explored the optimal conditions for ferroelectric domains to emerge on BiFeO₃ nanoislands. The authors used simulations to calculate the effects of geometry, free electric charges and domain boundary conditions for the 200- by 200- by 40-nanometer (width by length by height) nanoislands. Their simulations revealed that a nanoisland partially embedded into the substrate with a 45-degree beveled bottom edge minimizes the free energy and enables a stable configuration.

The simulations tracked the evolution of random polarization fields on nanoislands with different bottom-edge angles. Although a range of angles yielded a four-domain pattern on the surface of the nanoisland — with polarization vectors in each domain pointing toward the center — it was only near 45 degrees that the order penetrated into the bulk. The researchers also simulated the dynamics in the presence of an external electric field, showing that it is possible to switch to an alternate domain configuration in which the polarization in each region points away from the center. The authors say that their simulation approach may allow the design of low-power nanodevices that use ferroelectric order.

Source: “Understanding and predicting geometrical constraint ferroelectric charged domain walls in a BiFeO₃ island via phase-field simulations,” by Ren-Ci Peng, Xiaoxing Cheng, Ji Ma, Houbing Huang, Jing Ma, Long-Qing Chen, and Ce-Wen Nan, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5050802 .