Theoretical Framework for Modeling Field-Dependent Properties of Molecule-Based Magnetic Materials by using Spin-Flips

• Applicant: Dr. Sven Kähler, Ph.D.
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: from 2020 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 441274206

We plan to develop high-accuracy computer models to facilitate the design of new magnetic materials, specifically of single-molecule magnets (SMMs) and of molecular multiferroics (MFs) that display magneto-electric coupling. In SMMs unpaired electrons align their magnetic moments (their spins) to form a magnet. Major advantages of SMMs are their high density of magnetic centers and that their properties can be tuned by the chemical environment. This allows their application in novel data storage materials with up to 10000x higher information density compared to current materials. Also, SMMs can exhibit quantum behavior, allowing their use as qubits, the building blocks of quantum computers.MFs are materials with multiple ferroic properties, i.e. internal properties that can be switched by external influence, such as polarization switchable by an electric field or magnetization switchable by a magnetic field. In MFs with magneto-electric coupling (MEC), magnetic properties may also be switched by electric fields (and vice versa). Electric switching of magnetic properties is highly desirable since it is far easier to generate strong, quickly varying or spatially localized electric fields than magnetic ones. This opens up many applications in novel, smaller and more energy-efficient devices for sensing and for data processing and storage.Both SMMs and MFs rely on precise control over the interactions between spins which currently still require improvement to become application-ready: SMMs suffer from unwanted interactions so that their magnetization only remains stable for short times and at very low temperatures. MFs need stronger MEC for fast and efficient switching. Researchers use theoretical models called spin Hamiltonians to describe spin interactions. We propose a new way to parametrize these models using quantum chemical computations.In quantum chemical calculations on systems with multiple unpaired electrons, it is challenging to take into consideration the many different electron configurations that occur. Our innovation is to apply a spin-flip approach developed by my host Prof. Anna Krylov. Spin-flip calculations use so called high-spin states as a starting point, in which all unpaired electron spins are aligned, thereby forming a single configuration. From there, other important configurations are obtained by flipping individual spins.By calculating the spin Hamiltonian from first-principles, we will not only predict properties of candidate materials before they are synthesized but also identify design principles that optimize spin interactions for desired functionality.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Professorin Dr. Anna Krylov