Revealing the origin of magnetoresistance and resistive switching in organic spin valves

• Applicant: Professor Dr. Georg Schmidt
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 313833732

After the first demonstration of an organic spin-valve (OSV) in 2004 [1] the magnetoresistance in these devices has mostly been interpreted as electrical injection and detection of spin polarized electrons leading to a kind of giant magnetoresistance. We have, however, shown in a number of experiments that at least in some prototypical OSV the magnetoresistance does not originate from transport through electronic states in the organic material [2] but rather from tunneling leading to tunneling magnetoresistance (TMR) [3] and tunneling anisotropic magnetoresistance (TAMR) [4]. In addition, resistive switching in organic spin valves has recently been reported [5] and thus added a new functionality besides the magnetoresistive properties. Nevertheless, the underlying physics which is necessary to optimize these effects in detail has never been sufficiently understood.The objectives of this project target a better understanding of the physics which lead to magnetoresistance and resistive switching in OSV by investigating the contributions of TAMR, TMR and their interplay with resistive switching. Only by identifying the different contributions and their origin will it be possible to maximize each of the effects and to finally understand whether or in what way OSV can be used for applications.To achieve this goal it is necessary to answer three questions:1) Which part of the spin valve is responsible for the occurrence and magnitude of each of the effects (single interface, both interfaces, bulk material properties)?2) Does the effect depend predominantly on one of the materials or merely on the material combination?3) What is the role of the fabrication details? Is the interface preparation crucial for the appearance of the effect(s)?The answers to these questions can be found by careful variation of the materials and material combinations as well as of the fabrication processes involved. With the experiments performed by our group over the last years, prototypical devices and processes for the investigation of each of the three effects have been developed which can be used as a starting point for these variations.

• DFG Programme: Research Grants