In this paper we will describe a concentrating photovoltaic (CPV) system featuring spectral separation of the solar radiation. The newly designed concentrator structure provides both the spectral separation and the solar light concentration. The two caustics generated by the CPV system are spaced apart in such a way to illuminate two dense arrays of single junction Si and InGaP cells. Each of these PV receivers operate in a spectral region where its solar cells best perform, and thus they can be optimized independently of each other. Tuning the cutoff wavelength of the spectral separation system, the overall system efficiency is expected to reach 29.5% even with simple single-junctions PV receivers

No abstract

We present an experimental investigation of the magnetization reversal process in Ni80Fe20(10 nm)/Cu/Co(10 nm) sub-micrometric circular discs for two different thicknesses of the Cu spacer (1 and 10 nm). Magnetic hysteresis loops were measured by the longitudinal magneto-optical Kerr effect and by resonant scattering of polarized soft x-ray. The results for the 10 nm thick Cu interlayer show a complex magnetization reversal process determined by the interplay between the interlayer dipolar interaction and the different reversal nucleation fields in the two layers. It is worth noting that, during the reversal process, the magnetization of the two layers remains in a nearly single domain state due to the dipolar coupling. These findings are confirmed by three-dimensional micromagnetic simulations. In contrast, when the Cu spacer is 1 nm thick both measurements and simulations show that the reversal is accomplished via the formation of a vortex state in both discs due to the presence of a ferromagnetic exchange coupling that competes with the dipolar interaction.

In a combined experimental and numerical study, we investigated the details of the motion and pinning of domain walls in isolated and interacting pennalloy triangular rings (side 2 /Lm, width 250 nm, and thickness 25 nm). To induce interaction between the rings, they were arranged either in vertical chains with an apex of each triangle in proximity to the edge center of the triangle above it or in horizontal chains where the proximity is between the adjacent corners of the triangles. Using longitudinal and diffraction magneto-optic Kerr effects, magnetic force microscopy, and micromagnetic simulations, we detennined the field dependence of the spin structure in the rings. In all cases the remnant state of each ring is an "onion" state characterized by two domain walls-one head to head the other tail to tail-pinned at the apexes. In isolated rings the magnetization reversal occurs between two onion states via the fonnation of an intennediate vortex state, which arises from the motion and annihilation of the two domain walls. In the case of the horizontal chains the reversal mechanism is unchanged except that the dipolar interaction affects the field range in which the rings are in the vortex state. In the case of vertical chains an additional intennediate state is observed during reversal. The new state involves a domain wall pinned at the center of the edge that is in close proximity to the apex of its neighbor, We show that the domain-wall motion in this last case can be modeled by a triple potential well. Because the new state requires that a domain wall be pinned at the neighboring apex, our observations can be viewed as a very elementary fonn of magnetic logic. PACS number(s): 75.60.Ch, 75.60.Jk, 78.20.Ls