Ultrafine particles of barium ferrite from a citrate precursor

Ultrafine particles of barium ferrite produced by the precursor method have sizes between 5 and 100 nm. These particles have relatively low magnetisations and high coercivities. Mössbauer spectra exhibit different relative areas for the 4f_iv and 2b sites compared to the bulk which partly explains the low magnetisations.     

A double-Gaussian approach to the moment distribution in amorphous metals

It is shown that a double-Gaussian-shaped probability distribution of moment directions is an adequate model of the spin structures in as-cast, stress-relieved and field-annealed samples of Fe₇₈B₁₃Si₉ at room temperature and in zero applied field. The distribution comprises the convolution of two independent Gaussian distributions, one in the ribbon plane, and the other normal to the ribbon plane. The double-Gaussian distribution is more physically realistic than some alternative models of the moment distribution in amorphous metals.     

Suitability of commercial colloids for magnetic hyperthermia

Commercial nanoparticles supplied by Chemicell, Micromod and Bayer-Schering were characterised with regard to their nanocrystalline diameter, hydrodynamic diameter, total iron content and relative ferrous iron content. Additionally, calorimetric measurements were taken using a 900 kHz AC magnetic field of amplitude 5.66 kA/m. It was found that those samples containing relatively high (>18%) ferrous content generated a substantially smaller (12% on average) intrinsic loss power (ILP) than those samples with a lower ferrous content. Two nominally identical Chemicell samples that differed only in their production date showed significantly different ILPs, attributed to a variation in batch-to-batch crystallite sizes. The highest ILP values in the cohort, ca. 3.1 nHm²/kg, were achieved for particles with hydrodynamic diameters of ca. 70 nm and nanocrystalline diameters of ca. 12 nm. These compare favourably with most samples prepared in academic laboratories, although they are not as high as the ca. 23.4 nHm²/kg reported for naturally occurring bacterial magnetosomes.     

Nanocrystal/Metal–Organic Framework Hybrids as Electrocatalytic Platforms for CO2 Conversion

The tunable chemistry linked to the organic/inorganic components in colloidal nanocrystals (NCs) and metal–organic frameworks (MOFs) offers a rich playground to advance the fundamental understanding of materials design for various applications. Herein, we combine these two classes of materials by synthesizing NC/MOF hybrids comprising Ag NCs that are in intimate contact with Al‐PMOF ([Al₂(OH)₂(TCPP)]) (tetrakis(4‐carboxyphenyl)porphyrin (TCPP)), to form Ag@Al‐PMOF. In our hybrids, the NCs are embedded in the MOF while still preserving electrical contact with a conductive substrate. This key feature allows the investigation of the Ag@Al‐PMOFs as electrocatalysts for the CO₂ reduction reaction (CO₂RR). We show that the pristine interface between the NCs and the MOFs accounts for electronic changes in the Ag, which suppress the hydrogen evolution reaction (HER) and promote the CO₂RR. We also demonstrate a minor contribution of mass‐transfer effects imposed by the porous MOF layer under the chosen testing conditions. Furthermore, we find an increased morphological stability of the Ag NCs when combined with the Al‐PMOF. The synthesis method is general and applicable to other metal NCs, thus revealing a new way to think about rationally tailored electrocatalytic materials to steer selectivity and improve stability.     

Celtic gold coins in the light of Mössbauer spectroscopy, electron microprobe analysis and X-ray diffraction

Celtic gold coins found in Southern Germany were studied by Mössbauer spectroscopy, electron microprobe analysis and X-ray diffraction with special attention to coins rich in silver and copper. In such coins the electron microprobe analyses reveal a gold enrichment in a surface layer of more than 100 μm thickness. ¹⁹⁷Au conversion electron Mössbauer spectroscopy also shows that the surface of the coins consists of two phases, one of which is strongly enriched in gold compared to the bulk composition. In comparison with laboratory experiments the observed phenomena suggest that coin production in Celtic times may have involved deliberate heating and etching steps to enrich the surface layer in gold by depleting it of silver and copper.     

The effect of misalignment on the spin-flop transition in K2FeF5

Spin-flop transitions in K₂FeF₅ subject to an applied field (i) parallel to the easy axis, and (ii) directed at 33° to the easy axis are found to be (i) abrupt and (ii) smooth, in accordance with theoretical predictions.