Deterministic optical control of room temperature multiferroicity in BiFeO₃ thin films

Optical control of multiferroics is of great interest for optoelectronics applications yet has remained challenging and has rarely been reported at ambient temperatures. Chiu et al demonstrate the deterministic and reversible control of multiple ferroic orders in a thin film of the multiferroic BiFeO₃ (BFO) at room temperature. In particular, they show the light-induced transformation of a local tetragonal BFO phase to mixed phase, as well as light-induced conversion back to pure tetragonal BFO. To disentangle the mechanism of optoelectronic control, the authors use piezo force microscopy to generate the initial polarization followed by the correlated use of PFM, Kelvin probe microscopy, and conductive atomic force microscopy to map out the resultant phase, ferroelectric polarization, charge distribution, and conductivity. They find the local material transformation to be caused by laser-induced heating, aided by the facile interconversion of phases in mixed-phase BFO, and followed by flexoelectric polarization determining the final domain structure. Multiple multiferroic orders are controlled at once along with conductivity. 

In summary, the authors demonstrate and elucidate room temperature optical control of multiferroicity, taking an important step toward optoelectronic device applications, including nonvolatile random-access memory and data storage.