Controlling Chiral Spin States of a Triangular‐Lattice Magnet by Cooling in a Magnetic Field

Magnetic materials with a non‐collinear and non‐coplanar arrangement of magnetic moments hosting a nonzero scalar spin‐chirality exhibit unique magnetic and spin‐dependent electronic transport properties. The spin chirality often occurs in materials where competing exchange interactions lead to geometrical frustrations between magnetic moments and to a strong coupling between the crystal lattice and the magnetic structure. These characteristics are particularly strong in Mn‐based antiperovskites where the interactions and chirality can be tuned by substitutional modifications of the crystalline lattice. This study presents evidence for the formation of two unequal chiral spin states in magnetically ordered Mn_3.338Ni_0.651N antiperovskite based on density functional theory calculations and supported by magnetization measurements after cooling in a magnetic field. The existence of two scalar spin‐chiralities of opposite sign and different magnitude is demonstrated by a vertical shift of the magnetic‐field dependent magnetization and Hall effect at low fields and from an asymmetrical magnetoresistivity when the applied magnetic field is oriented parallel or antiparallel to the direction of the cooling field. This opens up the possibility of manipulating the spin chirality for potential use in the emerging field of chiral spintronics.     

Antiperovskites with Exceptional Functionalities

ABX₃ perovskites, as the largest family of crystalline materials, have attracted tremendous research interest worldwide due to their versatile multifunctionalities and the intriguing scientific principles underlying them. Their counterparts, antiperovskites (X₃BA), are actually electronically inverted perovskite derivatives, but they are not an ignorable family of functional materials. In fact, inheriting the flexible structural features of perovskites while being rich in cations at X sites, antiperovskites exhibit a diverse array of unconventional physical and chemical properties. However, rather less attention has been paid to these “inverse” analogs, and therefore, a comprehensive review is urgently needed to arouse general concern. Recent advances in novel antiperovskite materials and their exceptional functionalities are summarized, including superionic conductivity, superconductivity, giant magnetoresistance, negative thermal expansion, luminescence, and electrochemical energy conversion. In particular, considering the feasibility of the perovskite structure, a universal strategy for enhancing the performance of or generating new phenomena in antiperovskites is discussed from the perspective of solid-state chemistry. With more research enthusiasm, antiperovskites are highly anticipated to become a rising star family of functional materials.     

Antiperovskite Sr3MN and Ba3MN (M = Sb or Bi) as promising photovoltaic absorbers for thin-film solar cells: A first-principles study

Although lead halide perovskites (LHPs) have emerged as interesting photovoltaic (PV) absorbers for thin-film solar cells, the toxicity of Pb and poor materials stability have hindered the commercialization of solar cells using LHPs. Herein, using density functional theory (DFT) calculations, we suggest antiperovskite nitrides Sr₃MN and Ba₃MN (M = Sb or Bi) as potential Pb-free PV absorbers for thin-film solar cells. State-of-the-art DFT calculations based on the GW approximation show that these compounds have direct bandgaps suitable for PV applications. In addition, they exhibit significant absorption coefficients over 10⁵ cm⁻¹ for the visible light. By calculating spectroscopic limited maximum efficiency, we demonstrate that the film thicknesses of several hundred nanometers are enough for Sr₃MN and Ba₃MN to generate high-power conversion efficiencies over 20%. The analysis of the electron and hole effective masses reveals that these compounds have efficient carrier-diffusion paths allowing for the facile extraction of photocarriers. Lastly, we investigate the band alignments of the materials to help the design of thin-film solar cells.     

Key Role of Local Chemistry in Lattice Nitrogen-Participated N2-to-NH3 Electrocatalytic Cycle over Nitrides

Metal nitrides offer great opportunities for improving activity and selectivity of electrocatalytic nitrogen reduction reaction (ENRR) via the lattice nitrogen-participated mechanism. Understanding the role of local chemistry of lattice nitrogen is important for establishing rational design principles of nitride catalysts. Herein, high-throughput theoretical calculations are employed to investigate lattice nitrogen-participated ENRR over a family of antiperovskite nitrides (M′M₃N, M and M′ are different metal atoms) with highly tunable surrounding environments of N atoms. The M′M₃N structure comprises isolated N atoms in the center, M atoms in the first coordination shells, and M′ atoms in the second coordination shells. An appropriate M-N bond strength is found to be crucial for designing ideal nitride catalysts. Specifically, weak M-N bonding facilitates the participation of lattice nitrogen and better activity, but too weak M-N bonding results in structural instability of antiperovskite. The type of M element governs M-N bond strength through adjusting hybridization interactions between M orbital and N orbital, and the M′ element can further finely regulate M-N bond strength via M-M′ polarization effects. Finally, AgBa₃N, AlBa₃N, GaBa₃N catalysts are screened to possess greater ENRR activity than the benchmarking Ru (0001) catalysts and high selectivity toward hydrogen evolution reaction.