2D magnetic materials offer unprecedented opportunities for fundamental and applied research in spintronics and magnonics. Beyond the pioneering studies on 2D CrI₃ and Cr₂Ge₂Te₆, the field has expanded to 2D antiferromagnets exhibiting different spin anisotropies and textures. Of particular interest is the layered metamagnet CrSBr, a relatively air‐stable semiconductor formed by antiferromagnetically‐coupled ferromagnetic layers (T_c∼150 K) that can be exfoliated down to the single‐layer. It presents a complex magnetic behavior with a dynamic magnetic crossover, exhibiting a low‐temperature hidden‐order below T*∼40 K. Here, the magneto‐transport properties of CrSBr vertical heterostructures in the 2D limit are inspected. The results demonstrate the marked low‐dimensional character of the ferromagnetic monolayer, with short‐range correlations above T_c and an Ising‐type in‐plane anisotropy, being the spins spontaneously aligned along the easy axis b below T_c. By applying moderate magnetic fields along a and c axes, a spin‐reorientation occurs, leading to a magnetoresistance enhancement below T*. In multilayers, a spin‐valve behavior is observed, with negative magnetoresistance strongly enhanced along the three directions below T*. These results show that CrSBr monolayer/bilayer provides an ideal platform for studying and controlling field‐induced phenomena in two‐dimensions, offering new insights regarding 2D magnets and their integration into vertical spintronic devices.

The physical phenomenon of spin-crossover in molecular crystals is a multiscale process whose properties rely on the supramolecular organization of the spin-crossover active elements, their interactions within the crystal packing, and their dynamics. The delicate balance between short-range and long-range structural reorganizations upon the spin transition is at the origin of remarkable and fascinating physical phenomena such as thermal, light-induced and pressure-induced hysteresis, multi-step transitions, or multimetastablility. A complete understanding of the various phenomena associated with spin-crossover requires a comprehensive and thorough characterization of the overall structural architecture at all scales, which goes beyond the average static crystal structure. This Tutorial surveys the practical use of x-ray crystallography notably in non-ambient conditions to provide a direct view of the physical processes operating in spin-crossover molecular solids from bulk single crystals to nanocrystalline powder. Advanced x-ray crystallography methods are reviewed and illustrated with a series of model examples.

The dynamics of photoinduced phase transition in spin-crossover materials is studied using numerical simulations of a microscopic two-variable anharmonic model, in close connection with photocrystallographic experiments on the prototype system $\left[\text{Fe}{\left(\text{btr}\right)}_2{\left(\text{NCS}\right)}_2\right].{\text{H}}_2\text{O}$. A comparative analysis of the simulated diffraction pattern with excitation duration and intensity as variables is performed. Nonlinear dynamics, threshold effect in excitation intensity and light-induced phase separation are modeled and attributed to a strong electron-lattice coupling, mediated by long-range elastic interactions. Photoinduced nucleation and domain growth of the metastable high-spin phase is evidenced and quantitatively explained in the Avrami formalism.

A new, cheap, easy-to-synthesize and air-stable photoswitchable nickel(II) complex, QTNiNO₂, is reported. The metal centre in QTNiNO₂is coordinated by a nitro group and a [2-methyl-8-aminoquinoline]-1-tetralone ligand. The compound crystallizes in the tetragonal space groupI4₁/awith one complex molecule comprising the asymmetric unit, and the crystals are stable under ambient conditions. Irradiation of the solid-state form of QTNiNO₂with 530–660 nm LED light at 160 K converts the ambidentate nitro moiety fully to the nitrito linkage isomer which is stable up to around 230 K, as indicated by IR spectroscopy measurements. The structures of all species present in the examined crystals and their thermal stability were confirmed via X-ray multi-temperature and photocrystallographic experiments. The impact of temperature on the (photo)isomerization reaction taking place in a single crystal was additionally investigated. The experimental results are supported by computational analyses of crystal packing and intermolecular interactions that influence the isomerization process studied.