CoMOF5(pyrazine)(H2O)2 (M = Nb, Ta): Two-Layered Cobalt Oxyfluoride Antiferromagnets with Spin Flop Transitions

KMB4O6F3 (M = Co, Fe): two-dimensional magnetic fluorooxoborates with triangular lattices directed by triangular BO3 units

Frustrated magnetic systems are of great interest owing to their spin liquid state for application in quantum computing. However, experimentally, spin liquid has not been realized. Thus, experimental explorations of frustrated magnetic systems including triangular lattices are still urgent, particularly for directed synthesis compared to random exploration. Herein, for the first time, directed by the use of a triangular unit of the BO3 anion group, two novel layered magnetic fluorooxoborates KMB4O6F3 (M = Co 1, Fe 2) with triangular lattices have been hydrothermally synthesized and characterized. Compounds 1 and 2 are isostructural and crystallize in the P21/c space group with layered magnetic triangular lattices, which are further separated by K+ ions. Magnetic susceptibility curves of both 1 and 2 show no λ-anomaly peak down to a low temperature of 2 K in the absence of a magnetic long-range ordering transition, which are further confirmed by the heat capacity results. The magnetic-field dependence of magnetization at 2 K shows saturation of 2.20μB for 1 and 4.24μB for 2, respectively, at 7 T, after roughly subtracting the Van Vleck paramagnetic contribution. Further in-depth investigation of the underlying physics at a lower temperature below 2 K would be subsequently performed. Moreover, thermal stability and FT-IR and UV-vis-NIR spectroscopy with optical bandgap properties are also reported. Most importantly, our work provides a promising method to experimentally realize specific magnetic lattices (e.g. triangular lattices) directed by the use of triangular groups (e.g. BO3) as the functional unit.

Ferroelectrically tunable magnetic skyrmions in two-dimensional multiferroics

Magnetic skyrmions are topologically protected entities that are promising for information storage and processing. Currently, an essential challenge for future advances of skyrmionic devices lies in achieving effective control of skyrmion properties. Here, through first-principles and Monte-Carlo simulations, we report the identification of nontrivial topological magnetism in two-dimensional multiferroics of Co2NF2. Because of ferroelectricity, monolayer Co2NF2 exhibits a large Dzyaloshinskii-Moriya interaction. This together with exchange interaction can stabilize magnetic skyrmions with the size of sub-10 nm under a moderate magnetic field. Importantly, arising from the magnetoelectric coupling effect, the chirality of magnetic skyrmions is ferroelectrically tunable, producing the four-fold degenerate skyrmions. When interfacing with monolayer MoSe2, the creation and annihilation of magnetic skyrmions, as well as phase transition between skyrmion and skyrmion lattice, can be realized in a ferroelectrically controllable fashion. A dimensionless parameter κ' is further proposed as the criterion for stabilizing magnetic skyrmions in such multiferroic lattices. Our work greatly enriches the two-dimensional skyrmionics and multiferroics research.

Ligand vacancy channels in pillared inorganic-organic hybrids for electrocatalytic organic oxidation with enzyme-like activities

Simultaneously achieving abundant and well-defined active sites with high selectivity has been one of the ultimate goals for heterogeneous catalysis. Herein, we construct a class of Ni hydroxychloride-based inorganic-organic hybrid electrocatalysts with the inorganic Ni hydroxychloride chains pillared by the bidentate N-N ligands. The precise evacuation of N-N ligands under ultrahigh-vacuum forms ligand vacancies while partially retaining some ligands as structural pillars. The high density of ligand vacancies forms the active vacancy channel with abundant and highly-accessible undercoordinated Ni sites, exhibiting 5-25 fold and 20-400 fold activity enhancement compared to the hybrid pre-catalyst and standard β-Ni(OH)₂ for the electrochemical oxidation of 25 different organic substrates, respectively. The tunable N-N ligand can also tailor the sizes of the vacancy channels to significantly impact the substrate configuration leading to unprecedented substrate-dependent reactivities on hydroxide/oxide catalysts. This approach bridges heterogenous and homogeneous catalysis for creating efficient and functional catalysis with enzyme-like properties.