  The strain dependence of electric and magnetic properties has been widely
investigated, both from a fundamental science perspective and an applications
point of view. Electromechanical coupling through field-induced polarization
rotation (PRO) and polarization reorientation (PRE) in piezoelectric single
crystals can provide an effective strain in film/substrate epitaxial
heterostructures. However, the specific pathway of PRO and PRE is a complex
thermodynamic process, depending on chemical composition, temperature, electric
field and mechanical load. Here, systematic studies of the
temperature-dependent field-induced phase transitions in Pb(Mg,Nb)O3-PbTiO3
single crystals with different initial phase and orientation configurations
have been performed. Different types of strains, volatile/nonvolatile and
biaxial/uniaxial, have been measured by both macroscopic and in-situ X-ray
diffraction techniques. In addition, the strain state of epitaxial Mn-doped
CoFe2O4 thin films was examined by magnetic anisotropy measurements, where a
giant magnetoelectric coupling has been demonstrated.
