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Frustration of magnetic systems which is caused by competing interactions is the driving force of several unusual phenomena such as plateaus and jumps of the magnetization curve as well as of unusual energy spectra with for instance many singlet levels below the first triplet state. The antiferromagnetic cuboctahedron can serve as a paradigmatic example of certain frustrated anti ferromagnets. In addition it has the advantage that its complete energy spectrum can be obtained up to individual spin quantum numbers of s=3/2 (16777216 states). (C) 2008 Elsevier Ltd. All rights reserved.

The effect of confinement and energy transfer on the dynamics of a molecular magnet, known as a model system to study quantum coherence, is investigated. For this purpose the well-known polyoxovanadate [V15As6O42(H2O)](6-) (V-15) is incorporated into a protein (human serum albumin, HSA) cavity. Due to a huge overlap of the optical absorption spectrum of V, with the emission spectrum of a fluorescence center of HSA (containing a single tryptophan residue), energy transfer is induced and probed by steady-state and time-resolved fluorescence. The geometrical coordination and the distance of the confined V-15 to the tryptophan moiety of HSA are investigated at various temperatures. This effect is used as a local probe for the thermal denaturation of the protein at elevated temperatures.

Abstract Magnetic refrigeration is a highly active field of research. The recent studies in materials and methods for hydrogen liquefaction and innovative techniques based on multicaloric materials have significantly expanded the scope of the field. For this reason, the proper characterization of materials is now more crucial than ever. This makes it necessary to determine the magnetocaloric and other physical properties under various stimuli such as magnetic fields and mechanical loads. In this work, we present an overview of the characterization techniques established at the Dresden High Magnetic Field Laboratory in recent years, which specializes in using pulsed magnetic fields. The short duration of magnetic-field pulses, lasting only some ten milliseconds, simplifies the process of ensuring adiabatic conditions for the determination of temperature changes, Δ T a d . The possibility to measure in the temperature range from 10 to 400 K allows us to study magnetocaloric materials for both room-temperature applications and gas liquefaction. With magnetic-field strengths of up to 50 T, almost every first-order material can be transformed completely. The high field-change rates allow us to observe dynamic effects of phase transitions driven by nucleation and growth as well. We discuss the experimental challenges and advantages of the investigation method using pulsed magnetic fields. We summarize examples for some of the most important material classes including Gd, Laves phases, La–Fe–Si, Mn–Fe–P–Si, Heusler alloys and Fe–Rh. Further, we present the recent developments in simultaneous measurements of temperature change, strain, and magnetization, and introduce a technique to characterize multicaloric materials under applied magnetic field and uniaxial load. We conclude by demonstrating how the use of pulsed fields opens the door to new magnetic-refrigeration principles based on multicalorics and the ‘exploiting-hysteresis’ approach.

Workshop III at the IPS10-meeting was organized by H. Tributsch and F. Willig. The workshop consisted of three sessions, each taking place on a separate day with a duration of 80 minutes. Each session comprised three short key note lectures and a discussion period. The lectures addressed topics of fundamental importance for the understanding and utilization of photo-electrochemical processes at semiconductor electrodes. ; © 1995 Published by Elsevier Under a Creative Commons license Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). ; Published - 1-s2.0-0927024895800239-main.pdf

Abstract Magnetocaloric hydrogen liquefaction could be a ‘game-changer’ for liquid hydrogen industry. Although heavy rare-earth based magnetocaloric materials show strong magnetocaloric effects in the temperature range required by hydrogen liquefaction (77–20 K), the high resource criticality of the heavy rare-earth elements is a major obstacle for upscaling this emerging liquefaction technology. In contrast, the higher abundances of the light rare-earth elements make their alloys highly appealing for magnetocaloric hydrogen liquefaction. Via a mean-field approach, it is demonstrated that tuning the Curie temperature (T C) of an idealized light rare-earth based magnetocaloric material towards lower cryogenic temperatures leads to larger maximum magnetic and adiabatic temperature changes (ΔS T and ΔT ad). Especially in the vicinity of the condensation point of hydrogen (20 K), ΔS T and ΔT ad of the optimized light rare-earth based material are predicted to show significantly large values. Following the mean-field approach and taking the chemical and physical similarities of the light rare-earth elements into consideration, a method of designing light rare-earth intermetallic compounds for hydrogen liquefaction is used: tuning T C of a rare-earth alloy to approach 20 K by mixing light rare-earth elements with different de Gennes factors. By mixing Nd and Pr in Laves phase (Nd, Pr)Al2, and Pr and Ce in Laves phase (Pr, Ce)Al2, a fully light rare-earth intermetallic series with large magnetocaloric effects covering the temperature range required by hydrogen liquefaction is developed, demonstrating a competitive maximum effect compared to the heavy rare-earth compound DyAl2.

AbstractFast growth of sustainable energy production requires massive electrification of transport, industry and households, with electrical motors as key components. These need soft magnets with high saturation magnetization, mechanical strength, and thermal stability to operate efficiently and safely. Reconciling these properties in one material is challenging because thermally-stable microstructures for strength increase conflict with magnetic performance. Here, we present a material concept that combines thermal stability, soft magnetic response, and high mechanical strength. The strong and ductile soft ferromagnet is realized as a multicomponent alloy in which precipitates with a large aspect ratio form a Widmanstätten pattern. The material shows excellent magnetic and mechanical properties at high temperatures while the reference alloy with identical composition devoid of precipitates significantly loses its magnetization and strength at identical temperatures. The work provides a new avenue to develop soft magnets for high-temperature applications, enabling efficient use of sustainable electrical energy under harsh operating conditions.

Within this work the impact of contact materials with higher volume resistivity as leaded solder are investigated in terms of comparability of the current conduction through the joint. An approach was developed to experimentally determine the qualitative local current density by magnetic field imaging (MFI) at ribbon-to-ribbon contact samples. The result reveals that the MFI technique on a symmetric sample design allows the evaluation of the current paths in two-dimensional contact areas. Different resistivities of the contact material result in characteristic differences in current distribution through the joint. Low resistive Sn60Pb40-soldererd contacts exhibit localized current injection whereas the tested contact based on electrically conductive adhesives (ECAs) show an extended current flow through the ECA-based contact. A FEM-based simulation model to mimic the used setup was developed and confirmed the results by taking different contact material resistivities into account. For materials with resistivities larger than 1 · 10−3 Ω · cm current injection was found to spread-spatially within the tested contact geometry. Contact material development as well as contact design can benefit from that approach, allowing consumption and material composition optimization. A further advantage is the feasibility of the method to study production failures like inhomogeneous ECA distribution enabling a non-destructive monitoring of process stability and root cause analysis.

A local-magnetic-field-promoted photocatalytic overall water splitting system is developed for the Fe3O4/N-TiO2 catalyst, and an unprecedented solar-to-hydrogen efficiency of 11.9 ± 0.5% is achieved at 270 °C.