  Cross-coupling of ordering parameters in multiferroic materials by multiple
external stimuli other than electric field and magnetic field is highly
desirable from both practical application and fundamental study points of view.
Recently, mechanical force has attracted great attention in switching of
ferroic ordering parameters via electro-elastic coupling in ferroelectric
materials. In this work, mechanical force induced polarization and
magnetization switching were investigated in a polycrystalline multiferroic
Bi0.9La0.1FeO3 thin film using a scanning probe microscopy system. The
piezoresponse force microscopy and magnetic force microscopy responses suggest
that both the ferroelectric domains and the magnetic domains in Bi0.9La0.1FeO3
film could be switched by mechanical force as well as electric field. High
strain gradient created by mechanical force is demonstrated as able to induce
ferroelastic switching and thus induce both ferroelectric dipole and magnetic
spin flipping in our thin film, as a consequence of electro-elastic coupling
and magneto-electric coupling. The demonstration of mechanical force control of
both the ferroelectric and the magnetic domains at room temperature provides a
new freedom for manipulation of multiferroics and could result in devices with
novel functionalities.
