Successful PhD defense of André Farinha

Congratulations to André Farinha!

June 26, 2023

Title: “Emergent Magnetic Effects in Spintronic Devices with 3D Chiral Geometries

Three-dimensional magneto-electronic devices are expected to enable major improvements in memory density, uniquely 3D geometry-driven magnetic effects, and stabilize complex magnetic textures. However, achieving such 3D devices poses many great challenges, such as the development of new 3D fabrication and characterization techniques, new 3D modeling frameworks, the adaptation of the 2D fabrication toolset to 3D and the integration of all of the above.

In this thesis, we take a stepwise approach to the experimental demonstration of spintronic devices with complex 3D geometries and the novel effects they enable. First, a MPL system is developed to fabricate freeform 3D structures. Second, a simplified workflow for the fabrication of 3D spintronic devices is developed. By taking advantage of shadowing effects to establish the electrical contact pads, the workflow is simplified to comprise only two steps, the MPL fabrication of a scaffold and the magnetic film sputtering. Third, spintronic devices with chiral 3D geometries were fabricated and characterized. The geometrical chirality is seen to influence the magnetic properties of the systems, such that devices of opposite geometrical chirality present differentmagnetic responses, i.e., the chiral symmetry of the systems is broken. Two different studies were realized. In one study, current-induced DomainWall (DW) motion is characterized over μm wide ribbons with torsion. Different threshold currents and DWvelocities are measured for different DWconfigurations and torsion chiralities, enabling the realization of a selective DW filter. In the other study, coil-shaped devices display asymmetric AMR. The AMR responses are mirrored for coils of opposite chirality.

Finally, an improved MPL process is developed that enables in-situ real-time characterization and control of the 3D structure fabrication process, as well as the 3D reconstruction of the fabricated structure right after the fabrication.

The demonstrated workflow enables fast prototyping of spintronic devices with three-dimensional structures and is compatible with a wide range of different geometries. When integrated into spintronic devices, the newly demonstrated geometries are shown to lead to novel magnetic effects of substantial practical interest.The results in this thesis motivate further investigation into 3D nanomagnetism, while the methods presented herein can be used to prototype new 3D magneto-electronic devices and further demonstrate their promise.

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