Direct observation of spins at bathocuproine (BCP) interfaces: An electron spin resonance study on BCP/metal (Al or Au) thin films

We report an electron spin resonance (ESR) study of the layered thin films of bathocuproine (BCP) and metal (Al or Au). Clear ESR signals with g = 2.0030 were observed for the samples containing Al owing to gap states at BCP/Al interfaces, while no ESR signal was observed for the samples containing Au. The ESR analysis shows that the spins are magnetically isolated with a maximum spin concentration of 1.7% per BCP monomer. The activation energy of spin motion is found to be very low, approximately 1 K, supporting the enhanced electrical conductivity in BCP layers with gap states.