Dramatically enhanced polarization has been found for (001), (101), and (111) films, relative to that of BiFeO3 crystals. The easy axis of spontaneous polarization lies close to (111), for the various oriented films. BiFeO3 films grown on (111) have a rhombohedral structure, identical to that of single crystals; whereas films grown on (101) or (001) are monoclinically distorted from the rhombohedral structure, due to the epitaxial constraint.

In BiFeO3 films, it has been found that epitaxial constraint results in the destruction of a space modulated spin structure. For (111)c films, relative to corresponding bulk crystals, it is shown (i) that the induced magnetization is enhanced at low applied fields; (ii) that the polarization is dramatically enhanced; whereas, (iii) the lattice structure for (111)c films and crystals is nearly identical. Our results evidence that eptiaxial constraint induces a transition between cycloidal and homogeneous antiferromagnetic spin states, releasing a latent antiferromagnetic component locked within the cycloid.

The structural phase transformations of 0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 (PMN-30%PT) have been studied using x-ray diffraction (XRD) and neutron scattering as a function of temperature and electric field. We observe the phase transformational sequence (i) cubic (C) tetragonal (T) rhombohedral (R) in the zero-field-cooled (or ZFC) condition; (ii) C T monoclinic (M C ) monoclinic (M A ) in the field-cooled (or FC) condition; and (iii) R M A M C T with increasing field at fixed temperature beginning from the ZFC condition. Upon removal of the field, the M A phase is stable at room temperature in the FC condition, and also in the ZFC condition with increasing field. Several subtleties of our findings are discussed based on results from thermal expansion and dielectric measurements, including (i) the stability of the M A phase; (ii) a difference in lattice parameters between inside bulk and outside layer regions; and (iii) the diffuse nature of the M A and M C phase transition.

It has been found that aliovalent-substituted BiFeO 3 -PbTiO 3 -based polycrystalline materials have significantly enhanced multiferroic properties. Relative to unmodified BiFeO 3 , our results for modified BiFeO 3 -PbTiO 3 -based ceramics reveal: ͑i͒ a dramatic increase in the electric-field-induced polarization; and ͑ii͒ the establishment of a remanent magnetization. The results evidence the destruction of a space-modulated spin structure in bulk materials, via substituent effects, releasing a latent magnetization locked within the cycloid.

This paper develops and analyzes an equivalent circuit model of magnetic energy harvesters using reduced-order lumped element modeling (LEM) methods. This model is intended to enhance the design and analysis of a magnetic energy harvesting system by enabling direct physical insight into the system dynamics and simple circuit analysis techniques to extract all relevant performance parameters. Moreover, the model provides the ability to use circuit simulation software (e.g. PSPICE) to model the entire system in conjunction with nonlinear and/or active power electronic circuits. The circuit model is experimentally validated through electrical and mechanical measurements on a prototypical electromagnetic energy harvester.