CrSBr: An Air-Stable, Two-Dimensional Magnetic Semiconductor.

The discovery of magnetic order at the 2D limit has sparked new exploration of van der Waals magnets for potential use in spintronics, magnonics, and quantum information applications. However, many of these materials feature low magnetic ordering temperatures and poor air stability, limiting their fabrication into practical devices. In this Mini-Review, we present a promising material for fundamental studies and functional use: CrSBr, an air-stable, two-dimensional magnetic semiconductor. Our discussion highlights experimental research on bulk CrSBr, including quasi-1D semiconducting properties, A-type antiferromagnetic order (TN = 132 K), and strong coupling between its electronic and magnetic properties. We then discuss the behavior of monolayer and few-layer flakes and present a perspective on promising avenues for further studies on CrSBr.

Two-dimensional heavy fermions in the van der Waals metal CeSiI.

Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions1-6. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases7-11, which remains a significant challenge because traditional intermetallic heavy-fermion compounds have three-dimensional atomic and electronic structures. Here we report comprehensive thermodynamic and spectroscopic evidence of an antiferromagnetically ordered heavy-fermion ground state in CeSiI, an intermetallic comprising two-dimensional (2D) metallic sheets held together by weak interlayer van der Waals (vdW) interactions. Owing to its vdW nature, CeSiI has a quasi-2D electronic structure, and we can control its physical dimension through exfoliation. The emergence of coherent hybridization of f and conduction electrons at low temperature is supported by the temperature evolution of angle-resolved photoemission and scanning tunnelling spectra near the Fermi level and by heat capacity measurements. Electrical transport measurements on few-layer flakes reveal heavy-fermion behaviour and magnetic order down to the ultra-thin regime. Our work establishes CeSiI and related materials as a unique platform for studying dimensionally confined heavy fermions in bulk crystals and employing 2D device fabrication techniques and vdW heterostructures12 to manipulate the interplay between Kondo screening, magnetic order and proximity effects.

Concerted proton-electron transfer oxidation of phenols and hydrocarbons by a high-valent nickel complex.

The high-valent nickel(iii) complex Ni(pyalk)2 + (2) was prepared by oxidation of a nickel(ii) complex, Ni(pyalk)2 (1) (pyalk = 2-pyridyl-2-propanoate). 2 and derivatives were fully characterized by mass spectrometry and X-ray crystallography. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy confirm that the oxidation is metal-centered. 2 was found to react with a variety of phenolic and hydrocarbon substrates. A linear correlation between the measured rate constant and the substrate bond dissociation enthalpy (BDE) was found for both phenolic and hydrocarbon substrates. Large H/D kinetic isotope effects were also observed for both sets of substrates. These results suggest that 2 reacts through concerted proton-electron transfer (CPET). Analysis of measured thermodynamic parameters allows us to calculate a bond dissociation free energy (BDFE) of ∼91 kcal mol-1 for the O-H bond of the bound pyalk ligand. These findings may shed light onto CPET steps in oxidative catalysis and have implications for ligand design in catalytic systems.