Single-molecule anisotropic magnetoresistance at room temperature: Influence of molecular structure

Organic molecules featuring weak spin-orbit and hyperfine interactions show promise in the construction of effective spintronic devices. However, the impact of molecular structures on anisotropic magnetoresistance at the single-molecule level remains to be explored. In this work, we report systematic investigations on the construction and magnetoresistance of spintronic single molecule junctions of aliphatic dicarboxylic acids HOOC−(CH2)n−COOH (n=1−4) and conjugated benzenedicarboxylic acids HOOC-(C6H4)n-COOH (n=1-3) binding to Fe electrodes by employing electrochemically assisted jump-to-contact STM break junction technique (JTC-STM-BJ) under a constant of external magnetic field. Results show that single-molecule tunneling anisotropic magnetoresistance (AMR) of alkanedicarboxylic acids is independent of the molecular length and can reach as large as 44% (average), which is about twice that of benzenedicarboxylic acids. The almost same constant βN value but different contact conductance Gc with the applied magnetic field indicate that AMR arise from interface effect and spin injection. Besides Br substituent on the benzene ring can almost double the AMR by changing the spatial distribution of molecular charge density and frontier orbital characteristics. The present work shows that molecular structures play important roles in electron transport through single-molecule spintronic junctions.