Electron transport in magnetic van der waals materials and their heterostructures

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Doctoral Thesis

Electron transport in magnetic van der waals materials and their heterostructures

Date read: 2024-04-15 {_iPublic_txt_centro_}: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia) | ID: 10486/714985

Author: Martín Pérez, Lucía

Director: Burzuri Linares, Enrique

Abstract

Esta tesis tiene embargado el acceso al texto completo hasta el 15-10-2025 (General); This Thesis explores the temperature-dependent electrical response of two-dimensional (2D) van der Waals (vdW) magnetic materials and their heterostructures. Besides, significant efforts are dedicated to refining techniques to obtain 2D layers of these materials. This manuscript consists of six chapters. Chapter 1 introduces the field of low-dimensional magnetism. It covers the theory of magnetism, the discovery of 2D magnetic order in vdW materials and the fabrication of magnetic vdW heterostructures. Chapter 2 discusses the techniques and methods used to exfoliate magnetic vdW materials to obtain thin films, along with their integration into working electronic devices. It further elucidates the specifics of magnetic studies and electron transport measurements and explains the spectroscopic and microscopic techniques used. Chapter 3 describes optimized liquid phase exfoliation (LPE) routes to obtain mono- and few-layer flakes from: (i) FePS3, an Ising antiferromagnet, and (ii) cylindrite, a natural occurring vdW heterostructure showing glassy magnetism. The integrity, morphology and size distribution of the flakes is verified using spectroscopic and microscopic techniques. Chapter 4 explores the magnetic and electrical properties of thin LPE FePS3 flakes. Magnetic measurements in a SQUID magnetometer provides direct evidence of the antiferromagnetic transition in thin FePS3 flakes. Furthermore, solid-state electronic devices based on LPE FePS3 flakes are fabricated via dielectrophoresis, and low-temperature electron-transport measurements are performed. The results indicate a significant conductance across the flakes, sensitive to the antiferromagnetic order transition. Besides, a rich spectrum of electron transport excitations appears at low temperatures, including secondary magnetic transitions and potentially magnon-phonon hybrid states. Chapter 5 examines the electrical properties of the vdW heterostructure formed by FePS3 and graphene through electron transport measurements. The results suggest that the antiferromagnetic order of the FePS3 spins flake produces an alteration in graphene charge carriers analogue to an n-doping. Besides, an alternative approach to build magnetic heterostructures based on covalent chemistry is explored. The magnetic properties of LPE FePS3 flakes are preserved after the covalent functionalization. Lastly, Chapter 6 expands the formation of magnetic heterostructures with the grafting of a soft non-porous coordination polymer (npCP) onto graphene. The electrical characterization of the field effect transistors based on this heterostructure reveals that the magneto-structural transformations of the coordination polymer are detected as sharp increments in the electrical current and p-doping in graphene at the transition temperatures (Summary)

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