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Dipartimento di Fisica - Politecnico di Milano

Multi-functional materials and devices for spin-orbitronics and magnonics

The following activities will be carried out at PoliFab, the micro and nanofabrication facility of PoliMi. The duration of the thesis period is about 9 months.

 

• Berry phase engineering and spin-momentum locking control in topological materials and interfaces

The aim of this thesis work is to fabricate and characterize topological materials (such as Bi2Se3 and related compounds) and interfaces with antiferromagnetic and/or ferroelectric layers, to control the electrical transport in innovative devices exploiting the natural spin–momentum locking (correlation between spin orientation and momentum in topologically protected surface states) via Berry curvature engineering and symmetry breaking. During the thesis work, the student will fabricate the devices, exploiting the well-established deposition and patterning skills at Polifab, and characterize them by advanced magneto-electrical techniques in the Nanomag laboratory, exploiting bilinear magneto-resistance (BMER) and anomalous Hall effect (AHE) to probe the three-dimensional spin texture and interfacial exchange coupling in topological materials and heterostructures. The design and the interpretation of magneto-transport experiments will be supported by theoretical modelling and transport calculations in collaboration with a theoretical group.

Responsible: Matteo Cantoni
Partners: dr. Mario Cuoco, Spin-CNR (Salerno)

 

• Control of spin transport in the two-dimensional limit of the ferroelectric Rashba semiconductor SnTe

The work develops within the PRIN 2017 project TWEET (ToWards fErroElectricity in Two-dimensions), coordinated by CNR-SPIN (Chieti) and funded by MIUR. The project is inspired by the global thrust towards miniaturization and by the ubiquitous research in two-dimensional materials (2D). The goal of the project is the full control of ferroelectricity in few-layers films of multifunctional materials compatible with the standard silicon-based CMOS technology we all have in our pockets. The thesis @Polifab will focus on the chalcogenide SnTe (and GeTe). Belonging to ferroelectric Rashba semiconductors, SnTe is predicted to show a giant charge-to-spin conversion (spin Hall effect) controllable by the ferroelectric polarization. Tin telluride would allow for the non-volatile electric control of the spin transport in innovative spintronic devices beyond CMOS. Depending on the starting date and on the student preferences, the thesis work with deal with one or a few of the following activities: (1) epitaxial growth and characterization of 2D films of SnTe; (2) study of ferroelectricity in 2D SnTe; (3) realization of devices based on the ferroelectric control of the spin transport (spin valves, Datta-Das transistors, and other systems).

Responsible: Christian Rinaldi
Partners: Dr. Silvia Picozzi, CNR-SPIN (L’Aquila). Dr. Fabio Miletto, CNR-Na (Napoli). Dr. Ivana Vobornik, ELETTRA Synchrotron radiation facility (Trieste). Dr. Stefano Cecchi and Dr. Raffaella Calarco, Department of Epitaxy of the Paul Drude Institute (Berlin).


• Development of ultrasensitive MEMS magnetometers for medical application

This thesis work is part of the European project OxiNEMS. This project aims to develop ultrasensitive and robust magnetometers using N/MEMS technology in order to enable new diagnostic techniques such as the combination of Magnetoencephalography with Ultra-low field MRI.The thesis work will comprehend the following parts: (i) analytical and numerical study of the magnetometer working principle; (ii) design and simulation of MEMS magnetometers using Finite Element Method software; (iii) layout of device masks for cleanroom fabrication; (iv) cleanroom fabrication activities at PoliFAB; (v) characterization of fabricated devices; (vi) process optimization.

Responsible: Riccardo Bertacco
Supervisor: Federico Maspero

Partners: CNR-SPIN (Genova), Univerità Gabriele d’Annunzio (Chieti-Pescara), University of Hamburg (Hamburg), Chalmers University of Technology (CTH) (Göteborg).

 

•  Fabrication of free-standing magnetic membranes for spin polarimetry

The aim of this thesis work is to fabricate a two-dimensional spin filter, able to add the spin resolution to k- and energy-resolved photoemission experiments (ARPES), performed at radiation synchrotron facilities. The basic idea is to interpose a ferromagnetic membrane between the exit slit and the 2D detector of an electron analyser. This membrane will present a different transmission for electron with spin parallel or antiparallel to the magnetic moment of the magnetic layer, thus performing the spin filtering mechanism. In addition, the membrane must be self-sustaining, mechanically robust and almost transparent to the electron beam, in order to achieve a good spin selectivity without reducing too much the transmission. During the thesis work, the student will design and fabricate the membrane, by the combined use of deposition and lithography techniques, aiming at optimizing the geometry (ultrathin micrometric-size membranes embedded in a rigid framework) and the materials to achieve the desired targets (robustness, transmission and magnetic properties). To characterize the spin filtering properties, the spin-dependent transmission of a spin polarized electron beam, produced by an electron gun available at PoliFab, will be measured. Finally, first prototypes of the spin filters will be tested, with a true photoemission setup, at the APE beamline at the synchrotron light source of Elettra (Trieste).

Responsible: Matteo Cantoni
Partners: ELETTRA Synchrotron radiation facility (Trieste)