Pressure-Induced Antiferromagnetic to Nonmagnetic Phase Transition in a Heptacene Junction

Based on the first-principles method, the effect of pressure on the magnetism of heptacene molecules is investigated in a molecular junction. The results reveal an antiferromagnetic-nonmagnetic phase transition of heptacene during mechanical compression. The mechanism is explored by investigating the role of compression-induced structural deformations in molecular magnetism, embodied in both molecular structure and interfaces. The phase transition is attributed to the exchange of the dominant mechanism for molecular magnetism from electron-electron interaction to electronic hopping over a critical compression distance, which is mainly caused by the shortening of carbon-carbon bonds within the molecule and thus the enhancement of electronic delocalization. This work proposes a feasible way to manipulate the antiferromagnetism of organic molecules in molecular spintronic devices.