Hyo-Bin Ahn

The phase diagram and M – H curves of the metamagnetic regime of (Fe _{1− x} Co _x ) ₃ GaTe ₂ with x = 0.19–0.26 at various temperatures were studied.

Fe _x GeTe₂ (x = 3, 5) are two-dimensional ferromagnetic (FM) materials that have gained significant attention from researchers due to their relatively high Curie temperature and tunability. However, the methods for preparing FM nanoparticles (FNPs) and large-area Fe _x GeTe₂ films are still in the early stages. Here, we studied the magnetic properties of Fe _x GeTe₂ FNPs exfoliated via wet exfoliation in pure water. The coercive field of Fe₃GeTe₂ FNPs increases significantly, up to 60 times, while that of Fe₅GeTe₂ only slightly increases from that of bulk crystals. Further investigation related to the dimension of nanoparticles and the Henkel plot analysis reveals that the variation in their coercive field stems from the material’s thickness-dependent coercive field and the type of term that governs the interaction between single-domain nanoparticles. Our work demonstrates a facile method for preparing FNPs using van der Waals FM materials and tuning their magnetic properties.

When Ni is doped in Fe₃GaTe₂, the coercivity significantly increases even at room temperature, which is due to the domain pinning effect.

Ultrathin layered crystals of coordinated chromium(III) are promising not only as two-dimensional (2D) magnets but also as 2D near-infrared (NIR) emitters owing to long-range spin correlation and efficient transition between high and low-spin excited states of Cr3+ ions. In this study, we report on dual-band NIR photoluminescence (PL) of CrPS4 and show that its excitonic emission bifurcates into fluorescence and phosphorescence depending on thickness, temperature and defect density. In addition to the spectral branching, the biexponential decay of PL transients, also affected by the three factors, could be well described within a three-level kinetic model for Cr(III). In essence, the PL bifurcations are governed by activated reverse intersystem crossing from the low to high-spin states, and the transition barrier becomes lower for thinner 2D samples because of surface-localized defects. Our findings can be generalized to 2D solids of coordinated metals and will be valuable in realizing novel magneto-optic functions and devices.