  Multiferroics have received intense attention due to their great application
potential in multi-state information storage devices and new types of sensors.
Coupling among ferroic orders such as ferroelectricity, (anti-)ferromagnetism,
ferroelasticity, etc. will enable dynamic interaction between these ordering
parameters. Direct visualization of such coupling behaviour in single phase
multiferroic materials is highly desirable for both applications and
fundamental study. Manipulation of both ferroelectric and magnetic domains of
Bi5Ti3FeO15 thin film using electric field and external mechanical force is
reported, which confirms the magnetoelectric coupling in Bi5Ti3FeO15, indicates
the electric and magnetic orders are coupled through ferroelasticity. Due to
the anisotropic relaxation of ferroelastic strain, the back-switching of
out-of-plane electric domains is not as obvious as in-plane. An inevitable
destabilization of the coupling between elastic and magnetic ordering happens
because of the elastic strain relaxation, which result in a subsequent decay of
magnetic domain switching. Mechanical force applied on the surface of
Bi5Ti3FeO15 film generates by an AFM tip will effectively drive a transition of
the local ferroelastic strain state, reverse both the polarization and
magnetization in a way similar to an electric field. Current work provides a
framework for exploring cross-coupling among multiple orders and potential for
developing novel nanoscale functional devices.
