Magnetic and electric phase control in epitaxial EuTiO3_3 from first principles

We propose a design strategy - based on the coupling of spins, optical phonons, and strain - for systems in which magnetic (electric) phase control can be achieved by an applied electric (magnetic) field. Using first-principles density-functional theory calculations, we present a realization of this strategy for the magnetic perovskite EuTiO$_3$.Comment: Significantly revised for clarit

Ferroelectricity in the Dion-Jacobson CsBiNb2_2O7_7 from first principles

We have studied ferroelectricity in Dion-Jacobson CsBiNb$_2$O$_7$ from first principles. Using group-theoretical analysis and first-principles density functional calculations of the total energy and phonons, we perform a systematic study of the energy surface around a paraelectric prototypic phase. Our results suggest that CsBiNb$_2$O$_7$ is a ferroelectric with a polarization of P$_s$=40$\mu$C cm$^{-2}$. We propose further experiments to clarify this point

Ferroelectric Phase Transitions from First Principles

An effective Hamiltonian for the ferroelectric transition in $PbTiO_3$ is constructed from first-principles density-functional-theory total-energy and linear-response calculations through the use of a localized, symmetrized basis set of ``lattice Wannier functions.'' Preliminary results of Monte Carlo simulations for this system show a first-order cubic-tetragonal transition at 660 K. The involvement of the Pb atom in the lattice instability and the coupling of local distortions to strain are found to be particularly important in producing the behavior characteristic of the $PbTiO_3$ transition. A tentative explanation for the presence of local distortions experimentally observed above $T_c$ is suggested. Further applications of this method to a variety of systems and structures are proposed for first-principles study of finite-temperature structural properties in individual materials.Comment: 14 pages, harvmac, 4 uuencoded figure

Polarization enhancement in two- and three-component ferroelectric superlattices

Composition-dependent structural and polar properties of epitaxial short-period CaTiO_3/SrTiO_3/BaTiO_3 superlattices grown on a SrTiO_3 substrate are investigated with first-principles density-functional theory computational techniques. Polarization enhancement with respect to bulk tetragonal BaTiO_3 is found for two- and three-component superlattices with a BaTiO_3 concentration of more than 30%. Individual BaTiO_3 layer thickness is identified as an important factor governing the polarization improvement. In addition, the degree of inversion-symmetry breaking in three-component superlattices can be controlled by varying the thicknesses of the component layers. The flexibility allowed within this large family of structures makes them highly suitable for various applications in modern nano-electro-mechanical devices.Comment: The following article has been submitted to Applied Physics Letters. After it is published, it will be found at http://apl.aip.org

Physics of thin-film ferroelectric oxides

This review covers the important advances in recent years in the physics of thin film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin film form. We introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this we cover the enormous progress that has been made in the first principles computational approach to understanding ferroelectrics. We then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, we look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in non conventional nanoscale geometries.Comment: This is an invited review for Reviews of Modern Physics. We welcome feedback and will endeavour to incorporate comments received promptly into the final versio