Eicosane(C₂₀) Spin Channel Producing Magnetoresistance Effect on the Magnetic Tunnel Junction(MTJ) with Dissimilar Ferromagnetic Electrodes at Room Temperature

Connecting the two ferromagnetic thin-films of a magnetic tunnel junction via molecular bridges produces an unprecedented form of magnetic metamaterials for spintronics, with potential applications in energy-efficient data storage, memory devices, and next-generation quantum computing. In this study, we demonstrate, for the first time, the transformation of a bare MTJ (Co/NiFe/AlOx/NiFe) into a novel magnetic metamaterial using CH₃–C(=O)–S–(CH₂)₂₀–S–C(=O)–CH₃ (C20) molecules exhibiting intriguing properties at room temperature. This work primarily investigates the influence of C20 molecules on spin transport characteristics in MTJ. During fabrication of MTJ, the insulating AlO_x layer thickness was carefully chosen to be comparable to the molecular length, allowing C20 to bridge the exposed side edges of the MTJ's ferromagnetic electrodes. A series of experimental techniques was employed to analyze the impact of covalently bonded C20 spin channels between two ferromagnets, compared to a bare MTJ dominated by an AlOx insulator with interfacial and structural defects. Room-temperature transport measurements reveal a significant suppression of current from the microampere (µA) to picoampere (pA) range across multiple junctions, indicating a pronounced impact on the spin transport behavior of MTJ. Additionally, the tunneling current exhibits a distinctive oscillatory response under varying in-plane magnetic fields at room temperature. Electron spin resonance (ESR) spectroscopy measurements conducted on ~160,000 pillar-shaped MTJs further reveal a C20 molecule-induced enhancement of exchange coupling over a 25 micron MTJ area. Room-temperature Kelvin probe force microscopy (KPFM) was used to investigate the long-range C20 effects on the surface potential of MTJ cross-junctions. Our extensive range of experimental results highlights the potential of widely available and mass-producible C20 and MTJ-based magnetic metamaterials for tailoring spin-dependent transport in MTJs, paving the way for future applications in next-generation molecular spintronics devices.