Periodic Reporting for period 1 - SpinPhononHyb2D (Modelling spin-phonon coupling in hybrid molecular/2D materials)
Reporting period: 2023-04-01 to 2025-03-31
Molecules that can retain magnetisation in the absence of a magnetic field below a certain temperature called blocking temperature (TB) are called single-molecule magnets (SMM). SMMs have promising applications in fields such as information technologies, molecular spintronics and quantum computing. The spin-phonon coupling is the quantity that defines the efficiency of spin relaxation and represents one of the most urgent problems in the field of molecular magnetism. It strongly limits their working temperature, hindering the realization in fully functioning devices. The final and crucial step for the potential application of SMM-based devices is controlling their magnetic properties upon adsorption to the substrate. Among the substrates, two-dimensional magnetic (2D) layered materials have gained unprecedented interest due to their outstanding deformation capacity, which offers to control their properties by strain engineering. The use of spin waves (SWs, here quanta are known as magnons) instead of electric charge transportation in these 2D magnetic materials facilities has the potential to be applied in extremely low power consumption and miniaturization of magnonic devices.
The project SpinPhononHyb2D has a main objective the development of a fully ab initio strategy to predict the spin-phonon coupling of van der Waals (vdW) heterostructure of SMM adsorbed on 2D materials with the aim of designing potential SMM based nanodevices that can be tuned by chemical engineering. Therefore, through this project, we have explored the electronic and magnetic properties of (a) high-performance SMMs, (b) CrSBr and it lanthanide analogue layered vdW material as a function of reduced dimensionality and (c) hybrid vdW heterostructures formed by [CpTi(cot)], VOPc spin qubits and Fe-Pz spin-crossover molecules deposited on the surface of the air-stable 2D van der Waals ferromagnet CrSBr using first principles. In line with the main objectives above objectives, first-principles calculations have been performed, predicting and modelling the magneto-structural properties of new magnetic materials such as CrVO4 and USe3.
The project SpinPhononHyb2D has a main objective the development of a fully ab initio strategy to predict the spin-phonon coupling of van der Waals (vdW) heterostructure of SMM adsorbed on 2D materials with the aim of designing potential SMM based nanodevices that can be tuned by chemical engineering. Therefore, through this project, we have explored the electronic and magnetic properties of (a) high-performance SMMs, (b) CrSBr and it lanthanide analogue layered vdW material as a function of reduced dimensionality and (c) hybrid vdW heterostructures formed by [CpTi(cot)], VOPc spin qubits and Fe-Pz spin-crossover molecules deposited on the surface of the air-stable 2D van der Waals ferromagnet CrSBr using first principles. In line with the main objectives above objectives, first-principles calculations have been performed, predicting and modelling the magneto-structural properties of new magnetic materials such as CrVO4 and USe3.
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.
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.
These promising results lay a strong foundation for the development of advanced materials that integrate single-molecule magnets (SMMs) with two-dimensional (2D) magnetic materials. The work carried out in this project is expected to have a broad impact across the two primary research domains it bridges—molecular magnetism and spintronics—by deepening our understanding of spin relaxation mechanisms and interfacial interactions. The complementary expertise of the host and the experienced researcher, along with the effective exchange of knowledge between them, has been instrumental to the success of the project. Notably, ab initio calculations have proven to be a powerful tool for screening the magnetic potential and relaxation times of SMMs. Simultaneously, the determination of the Hubbard U parameter has played a critical role in advancing our understanding of the electronic and magnetic behavior of transition metal based layered materials. Although the project is grounded in fundamental science, the combination of key components—sublimable organic molecules (perylene, coronene, tetrathiafulvalene, and tetracyanoquinodimethane), spin qubits ([CpTi(cot)] and VOPc), and spin-crossover molecules (Fe-Pz), together with 2D ferromagnets (CrSBr, DySBr, DySI, and DySeI)—holds long-term potential, as emerging research in these rapidly evolving fields continues to gain momentum. The direct outcomes of this work will contribute to a more comprehensive understanding of magnetic relaxation in molecular nanomagnets and the role of interfacial interactions in hybrid molecular/2D magnetic material systems.