Chemical-bond effect on epitaxial strain in perovskite sodium niobate.

Epitaxial films and heterostructures of perovskite oxides attract tremendous scientific interest because of the unique phenomena therein. Especially important is the epitaxial growth of films subjected to substrate-induced misfit strain. We show here that in contrast to conventional misfit-controlled epitaxy, chemical bonds determine the crystal stability and strain in epitaxial films of sodium niobate on different cubic substrates. Strain relaxation in sodium niobate is independent of misfit magnitude and proceeds through perovskite-specific tilting of oxygen octahedra in addition to common defect formation. The observed structural relaxation evidences a major role of a large internal strain that originates from chemical bonds in the perovskite cell. The effect of chemical bonds on film strain is anticipated to also control the epitaxy of other perovskite oxides and related compounds.

Long Spin Diffusion Length in Few-Layer Graphene Flakes.

We report a spin valve with a few-layer graphene flake bridging highly spin-polarized La_{0.67}Sr_{0.33}MnO_{3} electrodes, whose surfaces are kept clean during lithographic definition. Sharp magnetic switching is verified using photoemission electron microscopy with x-ray magnetic circular dichroism contrast. A naturally occurring high interfacial resistance ∼12 MΩ facilitates spin injection, and a large resistive switching (0.8 MΩ at 10 K) implies a 70-130 µm spin diffusion length that exceeds previous values obtained with sharp-switching electrodes.

Dirty limit scattering behind the decreased anisotropy of doped YBa2Cu3O7-δ thin films.

We measured the resistivity of pulsed-laser-deposited BaCeO3 (BCO)-doped YBCO thin films containing spherical BCO particles in fields up to 30 T. The average diameter of the particles depends on the dopant concentration being below 4 nm in all the samples. Raised values of the upper critical field, Bc2, were observed in all the samples. Additionally, the parameter γ, describing the electron mass anisotropy, decreased from 6.2 in the undoped sample to 3.1 in the 8 wt.% BCO-doped sample. These results can be explained by the increased number of defects decreasing the mean free path of electrons and thus lowering the coherence length, which in turn increases Bc2.

Surface lattice resonances and magneto-optical response in magnetic nanoparticle arrays.

Structuring metallic and magnetic materials on subwavelength scales allows for extreme confinement and a versatile design of electromagnetic field modes. This may be used, for example, to enhance magneto-optical responses, to control plasmonic systems using a magnetic field, or to tailor magneto-optical properties of individual nanostructures. Here we show that periodic rectangular arrays of magnetic nanoparticles display surface plasmon modes in which the two directions of the lattice are coupled by the magnetic field-controllable spin-orbit coupling in the nanoparticles. When breaking the symmetry of the lattice, we find that the optical response shows Fano-type surface lattice resonances whose frequency is determined by the periodicity orthogonal to the polarization of the incident field. In striking contrast, the magneto-optical Kerr response is controlled by the period in the parallel direction. The spectral separation of the response for longitudinal and orthogonal excitations provides versatile tuning of narrow and intense magneto-optical resonances.

Schmallenberg virus in Dutch dairy herds: potential risk factors for high within-herd seroprevalence and malformations in calves, and its impact on productivity.

In November 2011, the new orthobunyavirus Schmallenberg virus (SBV) was identified in dairy cows that had induced fever, drop in milk production and diarrhoea in the Netherlands (Muskens et al., 2012. Tijdschrift voor Diergeneeskunde 137, 112-115) and a drop in milk production in cows in Northwestern Germany (Hoffmann et al., 2012. Emerging Infectious Diseases 18 (3), 469-472), in August/September 2011. This study aimed at quantifying risk factors for high within-herd prevalence of SBV and SBV-induced malformations in newborn calves in dairy herds in the Netherlands. Additionally, the within-herd impact of SBV infection on mortality rates and milk production was estimated. A case-control design was used, including 75 clinically affected case herds and 74 control herds. Control herds were selected based on absence of malformations in newborn calves and anomalies in reproductive performance. SBV-specific within-herd seroprevalences were estimated. Risk factors for high within-herd SBV seroprevalence (>50%) and the probability of malformed newborn calves in a herd were quantified. In addition, within-herd impact of SBV with regard to milk production and mortality was estimated. Animal-level seroprevalence was 84.4% (95% confidence interval (CI): 70.8-92.3) in case herds and 75.8% (95% CI: 67.5-82.5) in control herds. Control herds that were completely free from SBV were not present in the study. Herds that were grazed in 2011 had an increased odds (OR 9.9; 95% CI: 2.4-41.2)) of a high seroprevalence (>50%) compared to herds that were kept indoors. Also, when grazing was applied in 2011, the odds of malformations in newborn calves tended to be 2.6 times higher compared to herds in which cattle were kept indoors. Incidence of malformations in newborn calves at herd level was associated with both within-herd seroprevalence and clinical expression of the disease in adult cattle. The rate of vertical transmission of SBV to the fetus once a dam gets infected seemed low. A total of 146 stillborn or malformed calves were submitted by 65 farmers during the study period, of which 19 were diagnosed as SBV-positive based on pathological investigation and/or RT-qPCR testing of brain tissue. Based on these results combined with calving data from these herds we roughly estimated that at least 0.5% of the calves born between February and September 2012 have been infected by SBV. A drop in milk production was observed between the end of August 2011 and the first half of September (week 35-36), indicating the acute phase of the epidemic. During a 4-week period in which SBV infection was expected to have occurred, the total loss in milk production in affected dairy herds was around 30-51 kg per cow. SBV had no or limited impact on mortality rates which was as expected given the relatively mild expression of SBV in adult cows and the low incidence of malformations in newborn calves.

d0 ferromagnetic interface between nonmagnetic perovskites.

We use computational and experimental methods to study d(0) ferromagnetism at a charge-imbalanced interface between two perovskites. In SrTiO(3)/KTaO(3) superlattice calculations, the charge imbalance introduces holes in the SrTiO(3) layer, inducing a d(0) ferromagnetic half-metallic 2D hole gas at the interface oxygen 2p orbitals. The charge imbalance overrides doping by vacancies at realistic concentrations. Varying the constituent materials shows ferromagnetism to be a general property of hole-type d(0) perovskite interfaces. Atomically sharp epitaxial d(0) SrTiO(3)/KTaO(3), SrTiO(3)/KNbO(3), and SrTiO(3)/NaNbO(3) interfaces are found to exhibit ferromagnetic hysteresis at room temperature. We suggest that the behavior is due to the high density of states and exchange coupling at the oxygen t(1g) band in comparison with the more studied d band t(2g) symmetry electron gas.

Optical detection of hot-electron spin injection into GaAs from a magnetic tunnel transistor source.

Injection of spin-polarized hot-electron current from a magnetic tunnel transistor into GaAs is demonstrated by the observation of polarized light emission from a GaAs/In(0.2)Ga(0.8)As multiple quantum well light-emitting diode. Electroluminescence from the quantum wells shows a polarization of approximately 10% after subtraction of a linear background polarization. The polarization shows a strong dependence on the bias voltage across the diode, which may originate from changes in the electron spin relaxation rate in the quantum wells under varying bias conditions.

Kinetic physical etching for versatile novel design of well ordered self-affine nanogrooves.

Ion bombardment at extreme grazing incidence leads to the formation of remarkably well ordered, one to two atomic layer deep, parallel grooves on a Cu(001) surface. These self-organized grooves are oriented parallel to the ion's plane of incidence and their period can be controlled between approximately 4 and 15 nm. We have identified two distinct temperature regimes: Between about 200 and 300 K the substrate temperature controls the period, while below 200 to about 150 K the ion energy does. The groove separation distribution shows distinct self-affine character. The physical origin of the novel nanostructures is discussed.

Bowlby before Bowlby: the sources of an intellectual departure in psychoanalysis and psychology.

John Bowlby's first scientific papers express a viewpoint of the etiology of childhood disorders that gradually developed during his university years and the first years of his professional life. As becomes clear from, among other things, Bowlby's private correspondence, it was the period spent as a student at Cambridge, his work as a teacher at two progressive schools, and his work at a child guidance clinic that allowed him to articulate a view on childhood deviancy that was at variance with the Kleinian variant of psychoanalysis. Bowlby's position as an 'independent' thinker in the British Psycho-Analytical Society can be understood against the background of these intellectual influences.