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Dipartimento di Fisica - Politecnico di Milano

Crescita di eterostrutture, caratterizzazione, fabbricazione e test di dispositivi per elettronica di spin

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.

•  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)
 

• 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 (http://www.oxinems.eu/). 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).

 

• Advanced nanofabrication for magnonics and spintronics

This thesis work aims to explore new concepts in magnonics and spintronics, exploiting the control at the nanoscale of the static and dynamic magnetic properties of materials. This will be possible thanks to the combination of conventional nanofabrication techniques with thermally assisted magnetic Scanning Probe Lithography (tam-SPL), recently developed by the NaBiS group. By using a heatable nanometric probe of a Scanning Probe Microscope, it is possible to pattern point-by-point the magnetic properties, such as spin textures and magnetic anisotropies, of magnetic films, e.g. ferromagnets, synthetic antiferromagnets, antiferromagnets. In particular, the project will focus on the use of spin-waves, domain walls and topological quasi-particles, such as skyrmions and vortices, as information carriers in novel proof of concept devices for beyond CMOS computing. During the experimental thesis work at Polifab, the student will develop different experimental skills, starting from the growth and characterization of magnetic materials, to the nanofabrication, to the advanced characterization of magnetic properties, studying both the fundamental and technological aspects of spintronics. Space and time resolved magnetic characterization of the samples will be eventually carried out at the synchrotron (Swiss Light Source).

Responsible: Daniela Petti, Edoardo Albisetti
Partners: PSI (Villigen), NYU (New York), Università di Perugia (Perugia), CNR-IFN (Milano), IBM (Zurich)