Ferroelectric ferromagnets are exceedingly rare, fundamentally interesting multiferroic materials that could give rise to new technologies in which the low power and high speed of field-effect electronics are combined with the permanence and routability of voltage-controlled ferromagnetism. Furthermore, the properties of the few compounds that simultaneously exhibit these phenomena are insignificant in comparison with those of useful ferroelectrics or ferromagnets: their spontaneous polarizations or magnetizations are smaller by a factor of 1,000 or more. The same holds for magnetic- or electric-field-induced multiferroics. Owing to the weak properties of single-phase multiferroics, composite and multilayer approaches involving strain-coupled piezoelectric and magnetostrictive components are the closest to application today. Recently, however, a new route to ferroelectric ferromagnets was proposed by which magnetically ordered insulators that are neither ferroelectric nor ferromagnetic are transformed into ferroelectric ferromagnets using a single control parameter, strain. The system targeted, EuTiO(3), was predicted to exhibit strong ferromagnetism (spontaneous magnetization, approximately 7 Bohr magnetons per Eu) and strong ferroelectricity (spontaneous polarization, approximately 10 microC cm(-2)) simultaneously under large biaxial compressive strain. These values are orders of magnitude higher than those of any known ferroelectric ferromagnet and rival the best materials that are solely ferroelectric or ferromagnetic. Hindered by the absence of an appropriate substrate to provide the desired compression we turned to tensile strain. Here we show both experimentally and theoretically the emergence of a multiferroic state under biaxial tension with the unexpected benefit that even lower strains are required, thereby allowing thicker high-quality crystalline films. This realization of a strong ferromagnetic ferroelectric points the way to high-temperature manifestations of this spin-lattice coupling mechanism. Our work demonstrates that a single experimental parameter, strain, simultaneously controls multiple order parameters and is a viable alternative tuning parameter to composition for creating multiferroics.

Epitaxial strain is a proven route to enhancing the properties of complex oxides, however, the details of how the atomic structure accommodates strain are poorly understood due to the difficulty of measuring the oxygen positions in thin films. We present a general methodology for determining the atomic structure of strained oxide films via x-ray diffraction, which we demonstrate using LaNiO3 films. The oxygen octahedral rotations and distortions have been quantified by comparing the intensities of half-order Bragg peaks, arising from the two unit cell periodicity of the octahedral rotations, with the calculated structure factor. Combining ab initio density functional calculations with these experimental results, we determine systematically how strain modifies the atomic structure of this functional oxide.Comment: 23 pages, 11 figure

Abstract. Explicit and quantitative models for the spatial prediction of soil and landscape attributes are required for environmental modelling and management. In this study, advances in the spatial representation of hydrological and geomorphological processes using terrain analysis techniques are integrated with the development of a field sampling and soil-landscape model building strategy. Statistical models are developed using relationships between terrain attributes (plan curvature. compound topographic index, upslope mean plan curvature) and soil attributes (A horizon depth, Solum depth, E horizon presencelabsence) in an area with uniform geology and geomorphic history. These techniques seem to provide appropriate methodologies for spatial prediction and understanding soil landscape processes.

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Metal oxide semiconductor field-effect transistors, formed using silicon dioxide and silicon, have undergone four decades of staggering technological advancement. With fundamental limits to this technology close at hand, alternatives to silicon dioxide are being pursued to enable new functionality and device architectures. We achieved ferroelectric functionality in intimate contact with silicon by growing coherently strained strontium titanate (SrTiO3) films via oxide molecular beam epitaxy in direct contact with silicon, with no interfacial silicon dioxide. We observed ferroelectricity in these ultrathin SrTiO3 layers by means of piezoresponse force microscopy. Stable ferroelectric nanodomains created in SrTiO3 were observed at temperatures as high as 400 kelvin.

Gauss's law dictates that the net electric field inside a conductor in electrostatic equilibrium is zero by effective charge screening; free carriers within a metal eliminate internal dipoles that may arise owing to asymmetric charge distributions. Quantum physics supports this view, demonstrating that delocalized electrons make a static macroscopic polarization, an ill-defined quantity in metals--it is exceedingly unusual to find a polar metal that exhibits long-range ordered dipoles owing to cooperative atomic displacements aligned from dipolar interactions as in insulating phases. Here we describe the quantum mechanical design and experimental realization of room-temperature polar metals in thin-film ANiO3 perovskite nickelates using a strategy based on atomic-scale control of inversion-preserving (centric) displacements. We predict with ab initio calculations that cooperative polar A cation displacements are geometrically stabilized with a non-equilibrium amplitude and tilt pattern of the corner-connected NiO6 octahedral--the structural signatures of perovskites--owing to geometric constraints imposed by the underlying substrate. Heteroepitaxial thin-films grown on LaAlO3 (111) substrates fulfil the design principles. We achieve both a conducting polar monoclinic oxide that is inaccessible in compositionally identical films grown on (001) substrates, and observe a hidden, previously unreported, non-equilibrium structure in thin-film geometries. We expect that the geometric stabilization approach will provide novel avenues for realizing new multifunctional materials with unusual coexisting properties.

Using resonant x-ray spectroscopies combined with density functional calculations, we find an asymmetric biaxial strain-induced d-orbital response in ultrathin films of the correlated metal LaNiO3 which are not accessible in the bulk. The sign of the misfit strain governs the stability of an octahedral "breathing" distortion, which, in turn, produces an emergent charge-ordered ground state with an altered ligand-hole density and bond covalency. Control of this new mechanism opens a pathway to rational orbital engineering, providing a platform for artificially designed Mott materials.

Nature 466, 954-958 (2010) This Letter determined that EuTiO 3 , when appropriately strained, becomes a strong ferroelectric ferromagnet, in agreement with prediction. Strong ferroelectrics are proper ferroelectrics, having polarization as their order parameter, with high paraelectric-to-ferroelectric transition temperatures (T c ). Such ferroelectrics are manifested by a high T c and a high peak at T c in the dielectric constant versus temperature behaviour, signifying that ferroelectricity is driven by the soft mode, which is indicative of proper ferroelectricity. Our measurements of strained EuTiO 3 demonstrate both of these characteristics (shown in Fig. 3 of our Letter), and led us to conclude that strained EuTiO 3 is a strong ferroelectric. In contrast, all well-established prior single-phase ferroelectric ferromagnets are improper or pseudoproper ferroelectrics (that is, with weak ferroelectricity resulting in minuscule P s ). We did not present P s values in our Letter. Second harmonic generation measurements do not provide quantitative values of P s and attempts to determine P s via pyroelectric measurements (Yan, L., Li, J. F. & Viehland, D., personal communication)1 resulted in unphysically high values, presumably owing to electrical leakage. Nonetheless, the magnitude of the P s of our strained EuTiO 3 films can be estimated as follows. In their classic work, Abrahams, Kurtz, and Jamieson 1 established a correlation between P s and T c for displacive ferroelectrics. By studying numerous displacive ferroelectrics they found 5) where T c is the paraelectric-to-ferroelectric transition temperature in K, Dz is the atomic displacement of the 'homopolar' metal atom in Å , and P s is the spontaneous polarization of the ferroelectric in mC cm 22 . Combining these equations to eliminate Dz allows P s to be estimated from T c in displacive ferroelectrics. The huge anomaly of the soft optical phonon near T c that we observe ( Supplementary Fig. 1 of our Letter) shows that strained EuTiO 3 is a displacive ferroelectric, making the aforementioned correlation applicable. Plugging in our measured value of T c (Fig. 3 in our Letter) yields P s 5 29 6 2 mC cm 22 for our strained EuTiO 3 films from this established correlation. This rough estimate is consistent with our first-principles theoretical predictions-P s 5 21 mC cm 22 for EuTiO 3 under 11.1% biaxial tension, corresponding to the strain of our commensurate EuTiO 3 films grown on (110) DyScO 3 . Thus, the data in our Letter shows that appropriately strained EuTiO 3 is a strong ferroelectric ferromagnet.