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.
This thesis contains a selection of the results on the shallow electron states of quantum materials that I obtained as doctoral student of the Scuola di Dottorato in Fisica, Astrofisica e Fisica Applicata at the Università degli Studi di Milano. I carried out my doctoral research activity mostly at the TASC-IOM CNR laboratory, in the framework of the NFFA and APE-beamline facilities (Elettra Sincrotrone Trieste), as well in dedicated sessions at the I2; beamline of the Diamond light source, Harwell Campus, UK. To access the electronic properties of materials I specialised myself in photoemission spectroscopy techniques. High quality samples are a prerequisite for any attempt to study quantum materials so that a major effort in my PhD project has been to master the growth of novel quantum materials by means of Pulsed Laser Deposition (PLD). Given that the PLD is integrated in the suite of UHV facilities attached in-situ to the APE beamline, I directly characterised the electronic properties of the PLD grown samples exploiting both the spectroscopic techniques available at the beamline (ARPES, X-ray photoemission and absorption spectroscopies: XPS and XAS), either ex-situ structural characterisation tools (X-ray diffraction –XRD– and X-ray reflectivity, XRR).
Titanium dioxide (TiO2) is mainly present in nature in three different polymorphs: rutile, brookite and anatase. In particular, the latter is largely studied due to its promising future applications in several devices like memristors and solar cells, as well as implementations in spintronics and transparent conductive oxides. In this framework, the most important physical quantity is certainly conductivity: it is thus fundamental to analyze and control the electronic properties of anatase with a particular attention to the surface, which plays a remarkable role in the previous applications.
Rutile TiO2 is thermodinamically favoured at the common ambient pressure and temperature, while anatase is favoured instead at the nanometric scale: for these reasons, thin films Pulsed Laser Deposition (PLD) enables a controlled and functionalized growth of anatase, thanks to the extreme versatility and accuracy of this technique.
This work was carried out at the NFFA (Nano Foundries and Fine Analysis) - APE (Advanced Photoelectric Effect) beamline, part of the CNR - IOM group, which exploits the synchrotron radiation emitted by the third generation storage ring Elettra. In particular, APE beamline is a state-of-the-art surface science laboratory, which includes a thin film pulsed laser deposition chamber connected through a multi-component ultra-high vacuum (UHV) system to two distinct endstations, where the electronic properties of the samples are analyzed with low energy (8 120 eV ) and high energy (150 1600 eV ) x-rays. It is thus possible to deposit thin films of the desired material and subsequently perform measurements with synchrotron light without exposing the sample to air, preventing an irreversible contamination of the surface.
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).
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:
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.