Cubic molecule anisotropy impacting long-range magnetic ordering on magnetic tunnel junction-based molecular...

This study investigates how molecular anisotropy influences the switchability of magnetic tunnel junction molecular spintronic devices (MTJMSDs). This theoretical study provides insights about experimentally observed >900% conductance increase at room temperature on Co/NiFe/AlOx/NiFe magnetic tunnel junction(MTJ) with Octametallic Molecular Clusters(OMC). Via thiol surface attachment to two ferromagnetic metal leads of MTJ, an array of paramagnetic, cyanide-bridged octametal complexes, [(pzTp)FeIII(CN)3]4[NiII(L)]4[O3SCF3]4 (1) [(pzTp) = tetra(pyrazol-1-yl)borate; L = 1-S(acetyl)tris(pyrazolyl)decane], were covalently linked onto the electrodes, forming a dominant spin conduction channel. Using extensive Monte Carlo simulations based on the Heisenberg model, we analyzed how anisotropy along the cubic molecular channels affects spin coupling between ferromagnetic electrodes and paramagnetic molecules. Our results identify a critical anisotropy threshold (A_m = 0.4) that fundamentally alters device behavior. Below this threshold, the molecules stabilize an antiparallel coupling between the ferromagnetic electrodes, maintaining well-aligned molecule spins. Above A_y = 0.4, the magnetic moment of the two ferromagnetic electrodes stabilizes in different directions with respect to the direction of molecular anisotropy. More importantly, around A_m = 0.4, two ferromagnetic electrodes stabilize in a superposition state; there is a significant probability of switching between the magnetic moments of both FM electrodes, switching between +1 and -1. These findings provide valuable insights for designing gate-controlled three-terminal molecular spintronic devices, as disclosed in a recent patent (P. Tyagi, 2023, US Pat. 11,621,345), enabling the variation in molecular anisotropy due to the gate voltage via the voltage-controlled magnetic anisotropy phenomenon, potentially enabling advancements in spin logic, magnetoresistive memory, and quantum computing.