The rise of organic magnetoresistance: materials and challenges
This paper provides a brief review of recent progress regarding the magnetoresistive effect observed in organic semiconductors (OMAR). While the physical phenomena associated with the application of a magnetic field are well-known for vertical devices using a non-magnetic material sandwiched between two ferromagnetic electrodes, large magnetic-field effects in devices in which the organic semiconducting layer is sandwiched between non-ferromagnetic electrodes came as a great surprise. Recently, immense OMAR, exceeding 1000%, was reported in devices based on organic blends designed for achieving thermally activated delayed fluorescence. Such effect is amongst the largest ones measured for non-magnetic bulk materials and opens a truly novel and intriguing physical scenario that paves the way for new applications in magnetic field sensing and organic spintronics. While the precise origin of these magnetic-field effects in organics is still a matter of debate and involves interactions between charged and uncharged species of different natures, here we present an overview of the OMAR effect that focuses on material design and molecular engineering strategies thus far employed in the field. Current ideas regarding the molecular and structural origins of OMAR along with a final outlook on molecular design are presented.