Competing Effects of Inter-Ferromagnetic Electrode Coupling and Paramagnetic Molecule Induced Exchange Coupling in Magnetic Tunnel Junction-Based Molecular Spintronics Devices

In magnetic tunnel junction based molecular spintronics device (MTJMSD), two ferromagnetic electrodes (FMEs) are connected by an insulator film, and molecular channels along the exposed sides of the FMEs. Here, we report a Monte Carlo simulation (MCS) study showing the impact of inter-FME coupling via the insulator on the MTJMSD’s magnetic properties. We varied the direct inter-FMEs coupling strength and nature (i.e., JLR) for different molecule-induced exchange coupling types. Antiferromagnetic JLR enhanced the effect of molecule induced antiferromagnetic coupling effect. Whereas ferromagnetic JLR directly competed with the opposite nature of molecule induced antiferromagnetic molecular coupling. We observed that positive JLR with a magnitude of ≈ 0.2 reversed the five times stronger molecule induced antiferromagnetic coupling. When JLR = 0, the device was able to assume both antiferromagnetic and ferromagnetic states solely based on the molecular coupling effect. MCS studies showed that when JLR increased beyond a critical level, the paramagnetic molecules' spin orientations transitioned to a highly disordered state. In the disordered state, the paramagnetic molecules did not produce any long-range effect on MTJMSD.