Magnetostructural effect in the multiferroic BiFeO3-BiMnO3 checkerboard from first principles.

Using first-principles calculations, we identify a magnetostructural effect in the BiFeO3-BiMnO3 nanocheckerboard that is not to be found in either the bulk parent compound or in BiFeO3-BiMnO3 superlattices with (001)-oriented Fe and Mn layers. The key role of the cation arrangement is explained by a simple model of the exchange coupling between cation spins, leading to magnetic frustration in the checkerboard. We also demonstrate that the atomic-scale checkerboard has a multiferroic ground state with the desired properties of each constituent material: polar and ferrimagnetic due to BiFeO3 and BiMnO3, respectively.

Probing nanoscale ferroelectricity by ultraviolet Raman spectroscopy.

We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature (Tc) in ferroelectric ultrathin films and superlattices. We showed that one-unit-cell-thick BaTiO3 layers in BaTiO3/SrTiO3 superlattices are not only ferroelectric (with Tc as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO3 layers adjacent to them. Tc was tuned by approximately 500 kelvin by varying the thicknesses of the BaTiO3 and SrTiO3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.

Multiferroic domain dynamics in strained strontium titanate.

Multiferroicity can be induced in strontium titanate by applying biaxial strain. Using optical second harmonic generation, we report a transition from 4/mmm to the ferroelectric mm2 phase, followed by a transition to a ferroelastic-ferroelectric mm2 phase in a strontium titanate thin film. Piezoelectric force microscopy is used to study ferroelectric domain switching. Second harmonic generation, combined with phase-field modeling, is used to reveal the mechanism of coupled ferroelectric-ferroelastic domain wall motion. These studies have relevance to multiferroics with coupled polar and axial phenomena.

Unusual behavior of the ferroelectric polarization in PbTiO3/SrTiO3 superlattices.

Artificial PbTiO3/SrTiO3 superlattices were constructed using off-axis rf magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ferroelectric polarization as the ratio of PbTiO3 to SrTiO3 was changed. For PbTiO3 layer thicknesses larger than the 3-unit cell SrTiO3 thickness used in the structure, the polarization is found to be reduced as the thickness is decreased. This observation confirms the primary role of the depolarization field in the polarization reduction in thin films. For the samples with ratios of PbTiO3 to SrTiO3 of less than one, a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed.

Ferroelectricity at the nanoscale: local polarization in oxide thin films and heterostructures.

Ferroelectric oxide materials have offered a tantalizing potential for applications since the discovery of ferroelectric perovskites more than 50 years ago. Their switchable electric polarization is ideal for use in devices for memory storage and integrated microelectronics, but progress has long been hampered by difficulties in materials processing. Recent breakthroughs in the synthesis of complex oxides have brought the field to an entirely new level, in which complex artificial oxide structures can be realized with an atomic-level precision comparable to that well known for semiconductor heterostructures. Not only can the necessary high-quality ferroelectric films now be grown for new device capabilities, but ferroelectrics can be combined with other functional oxides, such as high-temperature superconductors and magnetic oxides, to create multifunctional materials and devices. Moreover, the shrinking of the relevant lengths to the nanoscale produces new physical phenomena. Real-space characterization and manipulation of the structure and properties at atomic scales involves new kinds of local probes and a key role for first-principles theory.

Epitaxial BiFeO3 multiferroic thin film heterostructures.

Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.

Small-cell carcinoma of the lung manifesting as acute hepatic failure.

In this report, we describe four cases of small-cell carcinoma of the lung manifesting as acute hepatic failure. These cases were noteworthy for the presence of hepatomegaly and substantially increased serum lactate dehydrogenase and uric acid levels. The ratio of normalized serum lactate dehydrogenase to normalized serum alanine aminotransferase from the 4 cases reported herein (mean +/- SE, 3.63 +/- 1.10) was significantly greater than the ratio obtained from the 12 cases of nonmalignant fulminant hepatic failure (mean +/- SE, 0.46 +/- 0.18; P < 0.001). Chest radiographs and abdominal imaging studies showed no neoplastic process in three of the four cases. Postmortem examinations disclosed extensive infiltration of the liver by metastatic small-cell carcinoma of the lung. A review of the literature revealed 13 additional similar cases. We conclude that metastatic small-cell carcinoma of the lung should be considered in cases of acute hepatic failure associated with hepatomegaly, substantially increased lactate dehydrogenase levels in comparison with alanine aminotransferase values, and increased uric acid levels even if imaging studies show no lesion. A liver biopsy done early during the hospital course is appropriate for diagnosis and for prevention of inappropriate transfer of the patient to a liver transplant center.