Addressing the challenges of using ferromagnetic electrodes in the magnetic tunnel junction-based molecular spintronics devices
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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.
KeywordsMolecular devices NiFe Magnetic tunnel junction Paramagnetic molecules Nanoelectronics
A part of this study was supported by the National Science Foundation-Research Initiation Award (Contract # HRD-1238802), Department of Energy/National Nuclear Security Agency subaward (Subaward No. 0007701-1000043016). We thank the Air Force Office of Sponsored Research (Award #FA9550-13-1-0152) for facilitating the study of ferromagnetic electrode stability by providing instrumentation support. We also acknowledge the support from NIST’s Center of Nanoscience and Technology in facilitating the experimental studies in this paper. Pawan Tyagi thanks Dr. Bruce Hinds and the Department of Chemical and Materials Engineering at University of Kentucky for facilitating experimental work on tunnel junction-based molecular devices during Ph.D. Molecules for molecular device fabrication were produced by Dr. Stephen Holmes’s group. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of any funding agency and corresponding author’s past and present affiliations.
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