Structural transformations creating atomistic spin textures on-demand in the van der Waals layered magnet CrSBr

The observation of long-range magnetic order in few-to-single layers of two-dimensional van der Waals (vdW) magnets has sparked new interest in studying low-dimensional magnetism. However, the air-sensitivity of many 2-D magnets, such as CrI₃, hinders nanoscale investigations and potential applications. Recently, an air-stable 2-D magnet, CrSBr, has been rediscovered. It is a semiconductor with a bandgap of approximately 1.6 eV and a high Néel temperature of 145 K. It shows strong light-matter interaction, making it an ideal candidate to study magneto-transport and magneto-optical excitations at the atomically thin limit. The air-stable nature of CrSBr enables exciting opportunities for atomistic measurements and manipulation.

In my talk, I will establish CrSBr as a material platform that allows unprecedented nanoscale control over structural and hence magnetic properties. Specifically, I will show that controlled electron beam irradiation in a scanning transmission electron microscope induces a local phase transformation, which creates a new 2-D layered structure having its stacking orientation perpendicular to that in the original material. We elucidate the mechanism of the phase transformation by tracking individual atom column intensities and mapping local strains as the new phase nucleates and grows. We find that the phase transformation occurs through selective displacement and migration of Cr into the vdW gap between CrSBr layers to create a new nanoscale vdW structure locally embedded in the original CrSBr matrix. We believe this method of sculpting the phase transformation at the atomic scale can create on-demand spin textures with exotic properties and potentially useful applications in spintronics and quantum information processing.