Addressing the challenges of using ferromagnetic electrodes in the magnetic tunnel junction-based molecular spintronics devices

Addressing the challenges of using high-Curie temperature ferromagnetic (FM) electrodes is critical for molecular spintronics devices (MSDs) research. Two FM electrodes simultaneously chemically bonded with a thiol-functionalized molecule can produce novel MSDs to exploring new quantum mechanical phenomenon and computer technologies. For developing a commercially viable MSD, it is crucial to developing a device fabrication scheme that carefully considers FM electrodes’ susceptibility to oxidation, chemical etching, and stress-induced deformations during fabrication and usage. This paper studies NiFe, an alloy extensively used in present-day memory devices and high-temperature engineering applications, as a candidate FM electrode for the fabrication of MSDs. Our spectroscopic reflectance studies show that NiFe oxidized aggressively after heating beyond ~90 °C. The NiFe surfaces, aged for several months or heated for several minutes below ~90 °C, exhibited remarkable electrochemical activity and were found suitable for chemical bonding with the thiol-functionalized molecular device elements. NiFe also demonstrated excellent etching resistance against commonly used solvents and lithography related chemicals. Additionally, NiFe mitigated the adverse effects of mechanical stress by subsiding the stress-induced deformities. A magnetic tunnel junction-based MSD approach was designed by carefully considering the merits and limitations of NiFe. The device fabrication protocol considers the safe temperature limit to avoiding irreversible surface oxidation, the effect of mechanical stresses, surface roughness, and chemical etching. This paper provides foundational experimental insights in realizing a versatile MSD allowing a wide range of transport and magnetic studies.