Interplay between Octametallic molecular cluster spin channels and magnetic tunnel junction Magnetization: A Monte Carlo study

Molecular spintronics devices (MSD) offer significant potential for next-generation computing and memory applications. In our prior experimental studies, we have utilized cubic Octametallic Molecular cluster composed of iron and Ni atoms without understanding different spin states the molecule can attain when covalently bonded with the two ferromagnetic electrodes. This study investigates the behavior of normalized molecular spin ( S m ) alongside three key variables: total system magnetization ( M), molecular magnetization ( M m ), and free electron magnetization ( F m ), which represents the free electron component of local molecular magnetization, under various thermal energies. Using Monte Carlo simulations (MCS), we analyze these parameters within the framework of a magnetic tunnel junction-based molecular spintronics device (MTJMSD) composed of a cubic molecule. The focus is on the dependence of these four variables on biquadratic coupling strength ( b m ) and exchange couplings between localized atomic spin and nearest free electron spin ( J e 0 m ) , localized spin and free electron in the vicinity of nearest neighboring atom ( J e 1 m ) , two nearest free electrons ( J eem ) . All the exchange couplings impact were studied at different thermal energies ( kT). Our findings reveal complex interdependencies between these variables. For lower thermal energies ( k T ≤ 0.1 ) , molecular spin decreased sharply with increasing bm , indicating molecular spin settling in low state. At higher thermal energies ( k T = 0.5 ) , a non-monotonic relationship emerges with Sm peaking at intermediate bm values. Additionally, we observe that M increases more significantly with negative exchange couplings between local spin and free electron spin in the vicinity of nearest neighboring local spin at lower kT ; whereas positive magnitude of the same exchange coupling tends to stabilize the lower magnitude of M. Furthermore, the free electron spin ( F m ) increases with positive Jeem values, plateauing at higher coupling strengths and exhibiting a more gradual increase at higher temperatures. These results highlight the intricate balance between molecular coupling, exchange interactions, and thermal effects, providing critical insights for optimizing the performance and stability of molecular spintronic devices across different thermal energy regimes.