Mechanical control of polar order

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Bismuth ferrite (BiFeO3) is a model multiferroic material exhibiting coupled ferroelectric and ferroelastic properties.
• Deterministic control of BiFeO3 domain structure is challenging due to high switching fields and competing polarization variants.

Purpose of the Study:

• To identify and characterize a mechanically assisted polarization switching pathway in epitaxial BiFeO3 thin films.
• To investigate the effect of concurrent mechanical pressure on the switching energetics and domain structure of BiFeO3.

Main Methods:

• Utilized out-of-plane electric fields for polarization reversal in BiFeO3 thin films.
• Applied mechanical pressure concurrently with electric fields to study its influence on switching.
• Employed Piezoresponse Force Microscopy (PFM) to analyze domain structure and ferroelastic competition.

Main Results:

• Electric-field-only switching required approximately 4 volts, stabilizing coexisting polarization states.
• Concurrent mechanical pressure substantially reduced the coercive voltage, enabling spontaneous switching (down to 0 volts).
• Mechanical pressure was shown to suppress ferroelastic domain competition, lowering the energy barrier for polarization rotation and domain wall motion.

Conclusions:

• Mechanically assisted switching provides a pathway to fundamentally alter switching energetics in multiferroics.
• Mechanical energy acts as an effective tool for probing and manipulating coupled ferroelastic-ferroelectric interactions.
• This framework offers a general approach for controlling coupled order parameters in multiferroic oxides, with direct applications in device architectures requiring lower switching energy.