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Chemistry for 3D spintronics

Subject Area Physical Chemistry of Solids and Surfaces, Material Characterisation
Experimental Condensed Matter Physics
Term from 2018 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 406700532
 
Final Report Year 2023

Final Report Abstract

Spintronics are a recent branch of nanoscience based on controlling the interaction of the spin of conduction electrons with magnetization. In most cases, spintronic functionality requires that two or more materials are in electric contact through their interfaces, with each a few nanometers thick at most. While spintronic effects have been evidenced and exploited in planar devices consisting of physically deposited thin films, advances into densely packed three-dimensional spintronic device architectures rely on interdisciplinary approaches in which chemical methods enable the generation of complex multimaterial geometries. In particular, we envision that controlling the motions of magnetic domain walls in multilayer nanwires and nanotubes made by chemical methods will move the field beyond magnetoresistance effects and unlock low-power consumption / high-endurance / fast memories, which are emerging as the next-generation of components for cache memories in processors, and internet of things (IoT) applications. In the C3DS project, we exploited three types of templates to define cylinders: anodic alumina membranes, ion track-etch polycarbonate films, and electrospun carbonized fibers. Based on them, we synthesized solid wires, simple tubes, coaxially arranged bilayer tubes, as well as trilayer (coaxial core/shell/shell) wires combining ferromagnetic materials (most prominently nickel-cobalt alloys) with non-magnetic metals designed to carry high densities of electrical currents (Bi, Ir, Pt, Cu). We developed synthetic methods on the basis of galvanic plating (electrodeposition), electroless deposition (surface-catalyzed reduction of metal salts), and atomic layer deposition (ALD, a gas-phase deposition technique based on a cyclic repetition of surface reactions with molecular precursors resulting in the accretion of solid with atomic resolution at each cycle). Further preparative tools exploited as ancillaries included thermal evaporation and sputter-coating of metals, as well as surface functionalization with molecular self-assembled monolayers. A combination of exhaustive materials characterization with physical investigation (performed by the French project partner) using high-level experimental (magnetic force microscopy, time-resolved magnetic imaging by scanning transmission X-ray microscopy using the magnetic circular dichroic effect with polarized X-rays) and theoretical (micromagnetic simulation) method enabled us to deliver fundamental insight into the behavior of complex, three-dimensional magnetic objects and spintronic structures: • The structure and the energetics of magnetic domain walls depends not only on the material’s composition but also on its microcrystallinity. Surface roughness is the most important parameter affecting the pinning of domain walls in motion. All three parameters are adjustable based on the preparative methods. • Domain walls pushed by electrical currents are driven not only by the spin-Hall effect but also by Oersted fields. •Oersted field-driven domain wall motion can be faster than 100 m/s in chemically synthesized bilayer nanotubes. This input demonstrates the applicability of chemically synthesized spintronic elements to fast memory storage and processing.

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