Chemistry for 3D spintronics

• Applicants: Professor Dr. Julien Bachmann, Ph.D.; Professor Dr. Wolfgang Ensinger
• 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

Spintronics is worth billions in magnetic sensors, and is fast emerging in the semiconductor industry (MRAM). Devices use both effects of magnetoresistance (magnetization influencing electric current) and the reverse, spin-transfer torques (a spin-polarized current to reverse magnetization). Spintronics require several magnetic and non-magnetic materials in contact, with length scales a few nanometers. Thus, it was unlocked by progress in thin film technology, and developed as planar devices based on lithography.However, as sensors and memories are becoming mature, limitations in terms of functions or capacities are identified. Devices for sensing field efficiently equally in all three direction are required, which is difficult to achieve with planar technology. For memories, the competition for increased areal density is driving technology to 3D schemes, in which a large number of bits is stored in the depth. It is thanks to this that flash memory has become a leader recently.We will explore the synthesis and physics of building blocks for a 3D spintronics, based on tubes and core-shell tubes/wires. Top-down techniques face their limits to define these. Instead, we propose an interdisciplinary consortium with two chemistry groups and a spintronic end user. As an exploratory project, we focus on delivering a building block for the two major spintronic effects and type of application: 1. magneto-resistance in single (AMR) or core-shell trilayers (GMR or TMR), with sensors as background. 2. spin-torque and spin-Hall domain-wall motion in single or metal/ferro core-shell bilayers, with the 3D race-track memory as a potential application.In a device the tubes would be embedded vertically in a medium, in bottom-up pores or vias based on lithography. In this first step we focus on single objects freed from their template and inspected at a surface. Synthesis includes polymeric track-etched membranes and anodization of aluminum for templates, electro- (and electroless) plating and atomic layer deposition for both metal and insulating layers of the core-shell. Physical measurements consist of electrical contacting and magneto-resistance, combined with magnetic microscopy.While electrochemistry in pores has been used for decades to produce arrays or vertical wires, investigation on single wires, and spintronics in mind, is only emerging. Only a handful of reports exist on magnetic tubes. The project is exploratory, at the cross-roads of material science and spintronics. It is high risk/high-gain, promising disruptive concepts for integrated components. In the shorter run, it will provide a playground for new physics, predicted to occur with interplay of magnetism with curvature and the specific topology of tubes. Besides, another impact is to foster joint work between chemists and spintronic physicists, to address other aspects where physical methods face limits.The project is a resubmission, taking into account reviewers' comments.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partner: Dr. Olivier Fruchart