Fe nuclear resonance vibrational spectroscopic studies of tetranuclear iron clusters bearing terminal iron(iii)-oxido/hydroxido moieties.

Fe nuclear resonance vibrational spectroscopy (NRVS) has been applied to study a series of tetranuclear iron ([Fe]) clusters based on a multidentate ligand platform (L) anchored by a 1,3,5-triarylbenzene linker and pyrazolate or (butylamino)pyrazolate ligand (PzNH Bu). These clusters bear a terminal Fe(iii)-O/OH moiety at the apical position and three additional iron centers forming the basal positions. The three basal irons are connected with the apical iron center a μ-oxido ligand.

Multicaloric Cryocooling Using Heavy Rare-Earth Free La(Fe,Si)-Based Compounds.

The transition toward a carbon-neutral society based on renewable energies goes hand in hand with the availability of energy-efficient technologies. Magnetocaloric cooling is a very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, the current reliance on highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable.

High-Pressure Polymorphism in Silver Ferrite Delafossite, AgFeO.

The delafossites are a class of layered metal oxides that are notable for being able to exhibit optical transparency alongside an in-plane electrical conductivity, making them promising platforms for the development of transparent conductive oxides. Pressure-induced polymorphism offers a direct method for altering the electrical and optical properties in this class, and although the copper delafossites have been studied extensively under pressure, the silver delafossites remain only partially studied. We report two new high-pressure polymorphs of silver ferrite delafossite, AgFeO, that are stabilized above ∼6 and ∼14 GPa.

Robust magnetism and crystal structure in Dirac semimetal EuMnBiunder high pressure.

Dirac materials offer exciting opportunities to explore low-energy carrier dynamics and novel physical phenomena, especially their interaction with magnetism. In this context, this work focuses on studies of pressure control on the magnetic state of EuMnBi, a representative magnetic Dirac semimetal, through time-domain synchrotron Mössbauer spectroscopy inEu. Contrary to the previous report that the antiferromagnetic order is suppressed by pressure above 4 GPa, we have observed robust magnetic order up to 33.

Strong enhancement of magnetic ordering temperature and structural/valence transitions in EuPdS under high pressure.

We present a comprehensive study of the inhomogeneous mixed-valence compound, EuPdS, by electrical transport, X-ray diffraction, time-domain Eu synchrotron Mössbauer spectroscopy, and X-ray absorption spectroscopy measurements under high pressure. Electrical transport measurements show that the antiferromagnetic ordering temperature, , increases rapidly from 2.8 K at ambient pressure to 23.

Signature of Many-Body Localization of Phonons in Strongly Disordered Superlattices.

Many-body localization (MBL) has attracted significant attention because of its immunity to thermalization, role in logarithmic entanglement entropy growth, and opportunities to reach exotic quantum orders. However, experimental realization of MBL in solid-state systems has remained challenging. Here, we report evidence of a possible phonon MBL phase in disordered GaAs/AlAs superlattices.

Persistent polyamorphism in the chiton tooth: From a new biomineral to inks for additive manufacturing.

Engineering structures that bridge between elements with disparate mechanical properties are a significant challenge. Organisms reap synergy by creating complex shapes that are intricately graded. For instance, the wear-resistant cusp of the chiton radula tooth works in concert with progressively softer microarchitectural units as the mollusk grazes on and erodes rock.

Effects of Noncovalent Interactions on High-Spin Fe(IV)-Oxido Complexes.

High-valent nonheme Fe-oxido species are key intermediates in biological oxidation, and their properties are proposed to be influenced by the unique microenvironments present in protein active sites. Microenvironments are regulated by noncovalent interactions, such as hydrogen bonds (H-bonds) and electrostatic interactions; however, there is little quantitative information about how these interactions affect crucial properties of high valent metal-oxido complexes. To address this knowledge gap, we introduced a series of Fe-oxido complexes that have the same S = 2 spin ground state as those found in nature and then systematically probed the effects of noncovalent interactions on their electronic, structural, and vibrational properties.

Terminal Hydride Species in [FeFe]-Hydrogenases Are Vibrationally Coupled to the Active Site Environment.

A combination of nuclear resonance vibrational spectroscopy (NRVS), FTIR spectroscopy, and DFT calculations was used to observe and characterize Fe-H/D bending modes in CrHydA1 [FeFe]-hydrogenase Cys-to-Ser variant C169S. Mutagenesis of cysteine to serine at position 169 changes the functional group adjacent to the H-cluster from a -SH to -OH, thus altering the proton transfer pathway. The catalytic activity of C169S is significantly reduced compared to that of native CrHydA1, presumably owing to less efficient proton transfer to the H-cluster.

Aqueous Superparamagnetic Magnetite Dispersions with Ultrahigh Initial Magnetic Susceptibilities.

Superparamagnetic nanoparticles with a high initial magnetic susceptibility χ are of great interest in a wide variety of chemical, biomedical, electronic, and subsurface energy applications. In order to achieve the theoretically predicted increase in χ with the cube of the magnetic diameter, new synthetic techniques are needed to control the crystal structure, particularly for magnetite nanoparticles larger than 10 nm. Aqueous magnetite dispersions (FeO) with a χ of 3.

Iron isotopic fractionation between silicate mantle and metallic core at high pressure.

The +0.1‰ elevated Fe/Fe ratio of terrestrial basalts relative to chondrites was proposed to be a fingerprint of core-mantle segregation. However, the extent of iron isotopic fractionation between molten metal and silicate under high pressure-temperature conditions is poorly known.

A practical guide for nuclear resonance vibrational spectroscopy (NRVS) of biochemical samples and model compounds.

Nuclear resonance vibrational spectroscopy (NRVS) has been used by physicists for many years. However, it is still a relatively new technique for bioinorganic users. This technique yields a vibrational spectrum for a specific element, which can be easily interpreted.

Quantitative vibrational dynamics of the metal site in a tin porphyrin: an IR, NRVS, and DFT study.

We used a newer, synchrotron-based, spectroscopic technique (nuclear resonance vibrational spectroscopy, NRVS) in combination with a more traditional one (infrared absorption, IR) to obtain a complete, quantitative picture of the metal center vibrational dynamics in a six-coordinated tin porphyrin. From the NRVS (119)Sn site-selectivity and the sensitivity of the IR signal to (112)Sn/(119)Sn isotope substitution, we identified the frequency of the antisymmetric stretching of the axial bonds (290 cm(-1)) and all the other vibrations involving Sn. Experimentally authenticated density functional theory (DFT) calculations aid the data interpretation by providing detailed normal mode descriptions for each observed vibration.

Exploration of synchrotron Mössbauer microscopy with micrometer resolution: forward and a new backscattering modality on natural samples.

New aspects of synchrotron Mössbauer microscopy are presented. A 5 µm spatial resolution is achieved, and sub-micrometer resolution is envisioned. Two distinct and unique methods, synchrotron Mössbauer imaging and nuclear resonant incoherent X-ray imaging, are used to resolve spatial distribution of species that are chemically and magnetically distinct from one another.

Sound velocities of compressed Fe3C from simultaneous synchrotron X-ray diffraction and nuclear resonant scattering measurements.

The applications of nuclear resonant scattering in laser-heated diamond anvil cells have provided an important probe for the magnetic and vibrational properties of (57)Fe-bearing materials under high pressure and high temperature. Synchrotron X-ray diffraction is one of the most powerful tools for studying phase stability and equation of state over a wide range of pressure and temperature conditions. Recently an experimental capability has been developed for simultaneous nuclear resonant scattering and X-ray diffraction measurements using synchrotron radiation.

Phonon density of states and compression behavior in iron sulfide under pressure.

We report the partial phonon densities of states (DOS) of iron sulfide, a possible component of the rocky planet's core, measured by the 57Fe nuclear resonant inelastic x-ray scattering and calculate the total phonon DOS under pressure. From the phonon DOS, we drive thermodynamic parameters. A comparison of the observed and estimated compressibilities makes it clear that there is a large pure electronic contribution in the observed compressibility in the metallic state.