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Concepts and tools in molecular spintronics

Periodic Reporting for period 2 - COSMICS (Concepts and tools in molecular spintronics)

Reporting period: 2018-11-01 to 2020-10-31

With the constant downsizing of electronic devices, components reach a size down to the nanometer scale where quantum effects play a predominant role. A strong fundamental research effort as well as efficient modelling approaches are essential for further advances. In the search of approaches towards extreme miniaturization for shrinking electronic circuits, new fields have emerged. In the eighties, spintronics also known as spin-electronics arose from the observation of spin-dependent electron transport phenomena combining the transport properties of electrons and their spin at the origin of the magnetism. These new phenomena were rapidly exploited and integrated in components such as read heads of magnetic hard drives. Molecular electronics appeared at the same time as spintronics and is based on the integration of molecules in electronic components. COSMICS is a project in the field of molecular spintronics that combines spintronics and molecular electronics. Molecular spintronics emerged for several (sometimes-contradictory) reasons. Probably the most important feature is that molecules are much more versatile than solid-state solutions as they offer an almost infinite range of possibilities and their electronic, magnetic, and transport properties can be finely tuned. This profusion of molecule/substrate combination opens up new possibilities in terms of applications, most of them still unforeseen at the moment. However, in order to avoid getting lost in a myriad of options, a truly interdisciplinary approach as well as fundamental driving concepts are crucial to clear the way towards new practical solutions. In particular, an efficient modelling approach is needed to shorten the development process of materials-enabled products.

COSMICS has three main goals:
• Develop a fundamental understanding, guiding concepts and tools to scale up and systematize the search of new smart functional molecular designs
• Implement efficient, reliable and user-friendly modelling tools for the atomistic simulations of materials for technology development.
• Development of new spintronic devices or systems.
Here are the main achievements of the works performed during the first year

- Synthesis of new sublimable SCO (spin crossover) complexes.
- Attempt to integrate a 2D SCO coordination network in a functional device
- Characterization of molecular lattices of SCO molecules on various substrate.
- Modelling strategies for individual and networks of SCO complexes.
- Understanding of the underlying factors for fragmentation.
- Building of magnetic supramolecules from non-magnetic isolated molecules.
- Elucidation of the main driving forces governing the magneto-crystalline anisotropy of ferromagnet/molecules interfaces.
- Optimization of ad-hoc substrate for optimal study of anisotropic magnetoresistance
- Implementation of new functionalities in the software quantumATK.

Here are the main achievements of the works performed during the second period of the project (M13->M36)

- A New robust spin crossover neutral molecule has been synthetized. This compound sublimates, forming thin films without losing its integrity and the spin crossover properties on surface
- Electronic sensing of the spin crossover transition in thin films of sublimable molecular complexes using graphene.
- A reverse LIESST effect has been observed for a FeII spin-crossover molecule on a metallic surface. A New mechanism has been proposed to explain this unusual phenomenon.
- New intriguing interactions between the substrate and deposited molecules have been evidenced.
- New concepts have been explored to implement molecular spin switches on surfaces.
- Detailed analysis of New ways to tune the magnetocrystalline anisotropy
- Implementation of many New analyzing tools in QuantumATK.
- Implementation of many New functionalities in QuantumATK.
- Integration of new functionalities in the software quantumATK that are of particular interest for academic and industrial users working in the growing field of spintronics. These functionalities will shorten the development process of materials-enabled products.

- In the future, we want to define optimal conditions to give rise to the largest magneto-anisotropic effect.

- In the future, we wish to integrate SCO complexes in multi-functional electronic devices.