Tunable giant magnetoresistance ratio in bilayer CuPc molecular devices

We investigate the influence of the distance between the buffer layer and the central molecule on the electrical transport, spin-filter transport, magnetoresistance effects and thermoelectric properties of a bilayer CuPc molecular device with V-shaped zigzag-edged graphene nanoribbon (VZGNR) electrodes by combining density functional theory and the non-equilibrium Green's function. The results show that the spin-dependent total conductance and spin filter efficiency of the bilayer CuPc molecular device reach a maximum with a parallel spin configuration (PC) when the carbon atom at the edge of the electrode is in the center of the carbon atom at the edge of the bilayer molecules due to the stronger coupling interaction between the double-layer molecules and the leads. Moreover, the spin polarization of the bilayer CuPc molecular device is reversed at certain distances; there is a minimum spin filter efficiency (SFE) of -99.93448% and a maximum SFE of 97.91% observed in the anti-parallel spin configuration (APC) of the device and there is a minimum SFE of -26.03175% and a maximum SFE of 99.99996% observed with the PC at zero bias. The SFE oscillates with increasing considered bias voltage in the PC and APC when the distances are d = 0 Å and d = -1.06 Å, and a negative differential resistance (NDR) effect was observed. For the PC and APC, there is a giant magnetoresistance (MR) effect and the MR ratio exceeds 5.21 × 10⁷% (99.9996%), and the MR ratio oscillates with increasing considered bias voltage when d = 0 Å. The MR ratio could be reserved by applying a certain bias voltage. These transport behaviors can be well understood by analyzing the transmission spectra, projected density of states and scattering states. There are pure spin Seebeck coefficients and pure charge Seebeck coefficients at certain temperatures when the distances are certain values, which means that the corresponding temperature differences could produce pure spin current and pure charge current, respectively. Our results provide new ideas for designing ultrahigh-performance spintronic molecular devices.