Mechanical switching of nanoscale multiferroic phase boundaries

Tuning the lattice degree of freedom in nanoscale functional crystals is critical to exploit the emerging functionalities such as piezoelectricity, shape-memory effect, or piezomagnetism, which are attributed to the intrinsic lattice-polar or lattice-spin coupling. Here it is reported that a mechanical probe can be a dynamic tool to switch the ferroic orders at the nanoscale multiferroic phase boundaries in BiFeO₃ with a phase mixture, where the material can be reversibly transformed between the "soft" tetragonal-like and the "hard" rhombohedral-like structures. The microscopic origin of the nonvolatile mechanical switching of the multiferroic phase boundaries, coupled with a reversible 180 rotation of the in-plane ferroelectric polarization, is the nanoscale pressure-induced elastic deformation and reconstruction of the spontaneous strain gradient across the multiferroic phase boundaries. The reversible control of the room-temperature multiple ferroic orders using a pure mechanical stimulus may bring us a new pathway to achieve the potential energy conversion and sensing applications. A pure mechanical control of the nanoscale multiferroic phase boundaries is achieved in mixed-phase BiFeO₃, which is attributed to pressure-induced elastic deformation and reconstruction of the spontaneous strain gradient across the boundaries. This demonstrates a new pathway to reversibly control the multiple ferroic orders such as ferroelectricity, ferroelasticity, and so on.