Organic-inorganic hybrid spintronics

• Applicant: Professor Dr. Wulf Wulfhekel
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 316711411

The combination of spintronics and organic materials has recently led to the formation of the new field of organic spintronics. With the discoveries of effects like molecular magnetoresistance or organic magnetoresistance and devices like organic spin valves or spin-memristors, the main focus of the field was to induce a function in a device consisting of metallic or ferromagnetic leads in contact with organic molecules by the action of the electrodes on the molecules. This action includes effects inducing a spin-polarization in the molecules, pinning molecular magnetic moments to that of the substrate or modifying the molecular states and orbitals by the interaction with the electron gas of the substrates. Only recently, we demonstrated that also the opposite action can be of significantly size in revealing an exchange bias of thin Co films by the action of an antiferromagnetically ordered molecular film. In this project, we intend to expand our studies of the action of molecules on the ferromagnetic electrodes in order to realize multifunctional devices, in which structural transitions in molecules switch the magnetic properties of the electrodes. Two main ideas will be addressed. First, spin-crossover complexes that can be switched between a magnetic and a non-magnetic state by external stimuli like electric fields, light or temperature will be exchange coupled to thin ferromagnetic layers. By switching the conformation of the molecules and thus their spin state, we expect large changes in the magnetic moment, magnetic anisotropy and hysteresis in the magnetic substrate. We expect such effects to be enhanced by magneto- elastic coupling, thanks to the large size change between the two spin states of the molecules. Second, using ferroelectric molecular films, the high electric field at the interface to the ferromagnet can induce changes in the magnetic properties of the metal realizing a multiferroic hybrid system. The systems will be studied with a broad range of experimental techniques ranging from local probes like scanning tunnelling microscopy, atomic and magnetic force microscopy to spatially averaging techniques like X-ray circular magnetic dichroism, magneto-optical Kerr effect and transport measurements. By combining the know-how of the two principle investigators and their groups, this wide spectrum of techniques can be utilized to pinpoint the relevant physical interactions in these hybrid systems.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partner: Dr. Eric Beaurepaire (†)