Finite-Element Simulations of Light Propagation through Circular Subwavelength Apertures

Light transmission through circular subwavelength apertures in metallic films with surrounding nanostructures is investigated numerically. Numerical results are obtained with a frequency-domain finite-element method. Convergence of the obtained observables to very low levels of numerical error is demonstrated. Very good agreement to experimental results from the literature is reached, and the utility of the method is demonstrated in the investigation of the influence of geometrical parameters on enhanced transmission through the apertures

Identifying gaps between science and practitioners perspectives on land use: the case of managed realignment in the German Baltic coast

Through state-of-the art ecosystem modelling supported by ecological experimental data, the COMTESS Project (funding: German Federal Ministry of Education and Research) investigates potential synergies and trade offs in ecosystem service provision under different land-use scenarios in two German coastal areas till 2100. Overall goal is to explore alternative sustainable land-use strategies to best adapt to climate change. Two science-based land- use scenarios were developed for two study regions on the Baltic and North Sea coasts to contrast a business-as-usual scenario. We focus here on the Baltic Se case region. The underlying premise of these alternatives is managed realignment of current dikes inland for: 1) climate mitigation through wetland re-naturation or 2) multiple land use, including biomass harvesting for energetic purposes (Baltic Sea). Managed realignment is increasingly considered as a valid coastal defence strategy to lower long-term costs of hard coastal defence and restore critical coastal and experiments have been initiated since the 1990s in a number of northwest European countries. Though politically highly controversial and facing much public antagonism, managed realignment is effectively embedded in the current coastal management policy of the state of Mecklenburg Vorpommern on the German Baltic coast. Implementation, nevertheless, faces many obstacles. Project-based scenarios for the Baltic Sea were first evaluated by key regional and local policy, management and land use practitioners, each expert in their field of activity. Their evaluation and recommendations were subsequently used to develop a fourth land-use scenario. Using qualitative empirical social research methods we analyse divergences and convergences between expert views on the projects scenarios. We argue that managed realignment is currently being mainstreamed in science, policy and resource management arenas although representatives of local land users and inhabitants do not endorse this strategy and still foster a hard defence approach to coastal zone management. This is best illustrated in recurrent social mobilisation and resistance to managed realignment proposals. This points at important perception and preference gaps between science, policy and land users / inhabitants, which need to be resolved to formulate and implement sustainable and socially acceptable land use strategies

Perpendicular exchange bias and its control by magnetic, stress and electric fields

erpendicular exchange bias (PEB) involving perpendicular magnetic anisotropy (PMA) in both the antiferromagnetic (AF) pinning and the ferromagnetic (FM) sensor layer is expected to become important in future perpendicular recording and sensing devices. Further, because of the reduced spin dimensionality, PEB promises to be easier understandable than the conventional planar exchange bias (EB). In addition to its first realization using the Ising-type AF compounds FeF2 and FeCl2 we have tested control strategies of EB being alternative to the conventional magnetic and thermal ones. Indeed, specific symmetry properties of the pinning layer have been shown to enable mechanical (viz. piezomagnetic via FeF2) and electric control (viz. magneto-electric via Cr2O3) of EB, respectively. Electric control promises to become relevant for TMR devices in MRAM technology

Perpendicular exchange bias and its control by magnetic, stress and electric fields

erpendicular exchange bias (PEB) involving perpendicular magnetic anisotropy (PMA) in both the antiferromagnetic (AF) pinning and the ferromagnetic (FM) sensor layer is expected to become important in future perpendicular recording and sensing devices. Further, because of the reduced spin dimensionality, PEB promises to be easier understandable than the conventional planar exchange bias (EB). In addition to its first realization using the Ising-type AF compounds FeF2 and FeCl2 we have tested control strategies of EB being alternative to the conventional magnetic and thermal ones. Indeed, specific symmetry properties of the pinning layer have been shown to enable mechanical (viz. piezomagnetic via FeF2) and electric control (viz. magneto-electric via Cr2O3) of EB, respectively. Electric control promises to become relevant for TMR devices in MRAM technology

Models for the magnetic ac susceptibility of granular superferromagnetic CoFe/Al2_2O3_3

The magnetization and magnetic ac susceptibility, $\chi = \chi' - i \chi''$, of superferromagnetic systems are studied by numerical simulations. The Cole-Cole plot, $\chi''$ vs. $\chi'$, is used as a tool for classifying magnetic systems by their dynamical behavior. The simulations of the magnetization hysteresis and the ac susceptibility are performed with two approaches for a driven domain wall in random media. The studies are motivated by recent experimental results on the interacting nanoparticle system Co$_{80}$Fe$_{20}$/Al$_{2}$O$_{3}$ showing superferromagnetic behavior. Its Cole-Cole plot indicates domain wall motion dynamics similarly to a disordered ferromagnet, including pinning and sliding motion. With our models we can successfully reproduce the features found in the experimental Cole-Cole plots.Comment: 8 pages, 6 figure

Electric field and aging effects of uniaxial ferroelectrics Sr x Ba1-x Nb2O6 probed by Brillouin scattering

This study was supported in part by the Marubun Research Promotion Foundation and JSPS KAKENHI Grant Number JP17K05030.Static and dynamic heterogeneity of disordered system is one of the current topics in materials science. In disordered ferroelectric materials with random fields, dynamic polar nanoregions (PNRs) appear at Burns temperature and freeze into nanodomain state below Curie temperature (T C). This state is very sensitive to external electric field and aging by which it gradually switches into macrodomain state. However, the role of PNRs in such states below T C is still a puzzling issue of materials science. Electric field and aging effects of uniaxial ferroelectric Sr x Ba1-x Nb2O6 (x = 0.40, SBN40) single crystals were studied using Brillouin scattering to clarify the critical nature of PNRs in domain states below T C. On field heating, a broad anomaly in longitudinal acoustic (LA) velocity at low temperature region was due to an incomplete alignment of nanodomains caused by the interaction between PNRs. A sharp anomaly near T C was attributed to the complete switching of nanodomain to macrodomain state owing to the lack of interaction among PNRs. After isothermal aging below T C, the noticeable increase of LA velocity was observed. It was unaffected by cyclic temperature measurements up to T C, and recovered to initial state outside of a narrow temperature range above and below aging temperature.Japan Society for the Promotion of Scienc

Random Field Models for Relaxor Ferroelectric Behavior

Heat bath Monte Carlo simulations have been used to study a four-state clock model with a type of random field on simple cubic lattices. The model has the standard nonrandom two-spin exchange term with coupling energy $J$ and a random field which consists of adding an energy $D$ to one of the four spin states, chosen randomly at each site. This Ashkin-Teller-like model does not separate; the two random-field Ising model components are coupled. When $D / J = 3$, the ground states of the model remain fully aligned. When $D / J \ge 4$, a different type of ground state is found, in which the occupation of two of the four spin states is close to 50%, and the other two are nearly absent. This means that one of the Ising components is almost completely ordered, while the other one has only short-range correlations. A large peak in the structure factor $S (k)$ appears at small $k$ for temperatures well above the transition to long-range order, and the appearance of this peak is associated with slow, "glassy" dynamics. The phase transition into the state where one Ising component is long-range ordered appears to be first order, but the latent heat is very small.Comment: 7 pages + 12 eps figures, to appear in Phys Rev