This thesis completes my work as doctoral student of the Scuola di Dottorato in Fisica, Astrofisica e Fisica Applicata at the Universit`a degli Studi di Milano, that has been carried out since November 2019 at the Istituto Officina dei Materiali of the Consiglio Nazionale delle Ricerche (IOM-CNR) in the premises of the Elettra - Sincrotrone Trieste and FERMI@Elettra infrastructures and in the framework of the NFFA facility.
My experimental activity employed complementary spectroscopy and polarimetry techniques oriented to address the characterisation of electronic and spin properties of systems with decreasing dimensionality. This programme has been conducted by exploiting state-of-the-art infrastructures to generate visible, UV and EUV ultrashort pulses (tabletop lasers and HHG at NFFA-SPRINT laboratory) and soft X-ray synchrotron light (at Elettra, Diamond and ESRF synchrotron light sources).
I used photoemission as the main tool in my investigation, supplementing my results with absorption spectroscopy. I focused on three materials, Fe(001)-p(1x1)O/MgO, EuSn2P2 and VI3, of high interest in modern and next-generation magnetic devices.
In the three systems I studied the electronic band structure to identify key features hinting at the bound electrons behaviour. I investigated the properties of the magnetically ordered phases and found evidence of the reduced dimensionality in the emergence of atypical spin ordering and the increasingly manifest electron correlation phenomena.
The information retained by band electrons is critical to access the spin polarisation of the bands and to give insight into the effects of spatial confinement on the spin degree of freedom.

This thesis is focused the structural and spectroscopic characterization of multiferroic heterostructures composed of a thin film of iron, which is ferromagnetic, deposited on a bulk PMN-PT ([Pb(Mg1/3Nb2/3)O3]1−x–[PbTiO3]x) substrate, which is ferroelectric. The epitaxially grown interface between two mate-rials displays the magnetoelectric coupling. By applying an electric field across the thickness of the substrate (i.e. along the growth direction) it is possible to polarize and deform the ferroelectric crystal structure, thus manipulating the magnetic properties of the over-layer. In this work, we analyse how the two opposite polarized states of the PMN-PT affect the magnetic anisotropy of the iron overlayer and the role of morphology in this modifications. In particular the morphology represents an important factor in the magnetoelectric mechanisms that has been little investigated before.

The present thesis work has been performed within a new-born laboratory called Spin Polar-ization Research Instrument in the Nanoscale and Time domain (SPRINT laboratory), as apart of the research infrastructures circuit NFFA-Trieste (Nano Foundries and Fine Analysis -belonging to the wider NFFA-Europe circuit) and hosted in the experimental hall of the freeelectron laser FERMI@Elettra.The SPRINT laboratory rises as an answer to the urgent request of the scientific communityof extension of photoemission spectroscopies (PES), not only energy-, but possibly also angle-and spin-resolved, to the time domain in the sub-picosecond regime. The integration of a PESapparatus within a setup for stroboscopic measurements (that is in a pump-probe scheme) pavesthe way to time resolved study of the relaxation of optically populated electronic states, thusenabling the study the ultrafast dynamics of the excitations inside the materials, with greatbenefit from both the fundamental and the technological point of view.

In this work, I am going to present the main results of the scientific activity in which I was involved during my summer internship at CNR-IOM in Trieste (Italy) during the period, May 16, 2019 to August 10, 2019.

This report focuses on the magneto-optic Kerr effect (MOKE) investigations done on two set of samples.
The first set of samples regards the optimization of the deposition parameters of CoFeB, in order to obtain a sample with low coercive field and isotropic behavior. The aim is to obtain a soft isotropic ferromagnetic layer, for further implementation into ferroelectric/ferromagnetic heterostructures.
The second set regards a run of experiments with the aim of setting an exchange bias coupling by partially oxidizing the ferromagnetic layer through the substrate deoxidation. Here Fe (10 nm) ferromagnetic layer is deposited on substrate Lithium Niobate (LNZ).

La misura della polarizzazione in spin di un fascio di elettroni fotoemessi da una superficie ferromagnetica permette di studiare in modo diretto la struttura elettronica determinata dall’interazione di scambio e quindi il momento magnetico di spin del sistema, caratterizzandone il comportamento magnetico. Da una parte lo sviluppo del campo della spintronica, dall’altra la richiesta sempre crescente di strumenti e dispositivi di immagazzinamento e trattamento dati ad alte prestazioni, marcano la necessità di esplorare le configurazioni degli stati elettronici e le loro eccitazioni.

This thesis completes my work as doctoral student of the Scuola di Dottorato in Fisica, Astrofisica e Fisica Applicata at the Università degli Studi di Milano that has been carried out, starting in November 4236, mostly at the Laboratorio TASC of IOM-CNR3 in the premises of the Elettra - Sincrotrone Trieste and FERMI@Elettra infrastructures4, in the framework of the NFFA and APE-beamline facilites5, as well as by accessing international large scale infrastructures and laboratories. The activity has addressed the development of experimental methodologies and novel instrumentation oriented to the study of the dynamical properties of highly correlated materials after high energy excitation. The science programme has been carried out by exploiting ultrafast femtosecond probes from the optical regime (Ti-Sa lasers, fibre laser oscillators) to the extreme UV-soft X rays at FERMI, to the picosecond hard X-rays from the SPring-: and Diamond synchrotron radiation source. The sample synthesis of correlated oxides and its characterization has been performed within the NFFA facility and APE-group collaboration in Trieste as well as the design and construction of the all new laser High Harmonic Generation beam line NFFA-SPRINT and its end station for time resolved vectorial electron spin polarimetry.

One of the most fascinating challenges in modern solid state physics, both from a theoretical and an experimental point of view, is the comprehension of electron correlation and how it can aect the macroscopic properties of materials. Eects of electron correlation are extremely important in materials with open d and f electron shells, where electrons are conned in narrow orbitals and the interaction between the electrons internal degrees of freedom are enhanced. In fact these systems are known to display some of the most intriguing phenomena in condensed matter physics, such as:

• huge changes in the resistivity passing the metal-insulator transition in vanadium oxide or upon application of a magnetic eld in manganites;
• considerable volume changes across phase transitions in actinides and lanthanides;
• high superconductivity transition temperatures (above liquid nitrogen temperatures) in copper-oxygen planes based materials.

The possibility to exploit these properties to realise devices has driven many theoretical and experimental eorts directed to understand how to describe these phenomena and how to control them by manipulating external parameters such as temperature, doping, etc.

This thesis reports on the construction and commissioning tests of the novel experimental set-up needed for a long term research project, named ULTRASPIN, aiming at establishing time resolved spin-resolved photoemission measurements with ultra-short (10−14 s) photon pulses from Free Electron Laser beamlines or from table-top UV/Soft-X beamlines.

The ULTRASPIN project started in the summer 2013, building on competences and instrumentation in part available from the APE-beamline group of IOM-CNR at Elettra, and with the partial support of an European contract (EXSTASY-EXperimental STation for the Analysis of the Spin Dynamics, Grant agreement N.PIIF-GA-2012-326641) and related fellowship of a world-expert of Mott scattering.

I have been involved from the beginning in the final design, in the construction and commissioning of a novel stray-field free UHV apparatus for preparing and hosting atomically clean surfaces and for measuring the spin-polarization of the photo-emitted electrons with “single pulse” sensitivity down to the 10−14 s time scale, as well as in the standard high frequency spectroscopy mode. In the commissioning phase I have participated to test experiments on ULTRASPIN as well as to relevant experiments conducted in other apparatuses.