At the beginning of this project, first principles calculations were performed to analyze the modulation of electronic structure, magnetic properties, magnon dispersion and spin dynamics of air-stable 2D ferromagnet CrSBr by deposition of electron donor sublimable organic molecules such as perylene, coronene and tetrathiafulvalene (TTF) and electron acceptor molecule such as tetracyanoquinodimethane (TCNQ). The key finding of this work is the molecule-induced selective modulation of magnon propagation speed, reaching up to ~20%. Crucially, we demonstrate that interfacial charge transfer is the primary mechanism controlling spin wave modulation. This insight has significant implications for the rational design of future systems, as we show that (i) the energy offset between the molecular HOMO and the material’s conduction band minimum and (ii) the relative group velocities, both exhibit a linear relationship with the amount of charge transferred between the molecule and the substrate. This paves the way for high-throughput screening of molecular and magnetic materials to identify optimal hybrid heterostructures.
This methodology was applied to other vdW heterostructures formed by [CpTi(cot)] and VOPc spin qubits deposited on the surface of CrSBr. OOur results show that different molecular rotation configurations significantly impact qubit relaxation time and alter the magnon spectra of the underlying 2D magnet, allowing the chemically coherent control of spin waves in this material. We predict the feasibility of an ultrafast magnon-qubit interface with minimized decoherence, where exchange coupling plays a crucial role. This work opens new avenues for hybrid quantum magnonics, enabling selective tailoring through a versatile chemical approach.
Finally, we have deposited Fe-Pz spin-crossover molecule (SCO) on CrSBr. The SCO complexes, particularly based on Fe(II) coordination compounds, are at the forefront as they exhibit reversible switching from low spin (LS, S = 0) to high spin (HS, S = 2) state by the application of light, temperature, pressure or electric fields. We have analysed the effect of spin transition on the structural, electronic and magnetic properties of the CrSBr monolayer employing first-principles calculations. We have also taken into account the effect of intermolecular interaction or cooperativity in the spin transition. The effect of strain on CrSBr induced by molecular spin transition was studied by developing a mechanoelastic model. The strain allowed us to tune the magnons of CrSBr efficiently and, therefore, detect the molecular spin state by measuring them using an inelastic neutron scattering experiment.. This work laid the foundation of the first stepping stone for the development of novel frontiers of switchable magnetic devices.
Apart from studying the vdW heterostructure, we have performed a systematic investigation of the effects of Dy doping (12.5%, 25%, and 50%) on the structural, electronic and magnetic properties of the CrSBr monolayer. Our results reveal that Dy incorporation enhances magnetic anisotropy and modulates critical temperatures that arise from strong ferromagnetic and weak antiferromagnetic interactions. Additionally, we investigate the properties of DySBr, DySI and DySeI monolayers, which are isostructural to the CrSBr. Our results reveal the feasibility of exfoliating them down to the single layer and the presence of long-range magnetic order at low temperatures, relying on the combination of both weak exchange interactions and large spin-orbit coupling. This work provides insights into tuning the properties of CrSBr through rare earth doping, unlocking new possibilities for advanced applications at the 2D limit.
