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.