Engineering a multiferroic monodomain in BiFeO3 films through magnetoelastic control*

The presence of domains in ferroic materials can diminish their macroscopic properties and hence their usefulness in device applications. This effect is particularly limiting in multiferroic materials such as BiFeO3, which combine magnetic, ferroelectric and ferroelastic orders, and tend to grow with numerous domain variants in all three sectors. Here, we present the use of strain and electric fields to control the magnetic domain population in (111)-BiFeO3 films. This orientation maximises the out-of-plane polarisation but generally results in a texture of magnetic domains. By exploiting the magnetoelastic coupling between the magnetic and crystal structures, and measuring the resulting magnetic domain populations by magnetic x-ray and neutron diffraction, we demonstrate the use of substrate strain to engineer a ferroelastic, ferroelectric, and magnetic monodomain, coherent over an entire 1-micron-thick BiFeO3 film. We further demonstrate the coupling of the magnetic structure to the ferroelectric polarisation by showing the cycloidal rotation direction (magnetic polarity) is inverted upon 180-degree switching of the polarisation.