MAGNETOELECTRIC EFFECTS IN TWO-DIMENSIONAL MULTIFERROIC HETEROSTRUCTURES

Abstract

Magnetism, one of the fundamental physical properties, has revolutionized technologies ranging from data storage to biomedical imaging and continues to bring forth new phenomena in emerging materials with reduced dimensionalities. The recent rise of two-dimensional (2D) van der Waals (vdW) magnets offers a compelling platform for exploring magnetoelectric effects, owing to their wide property tunability, excellent compatibility with other materials, and rich interfacial coupling physics. These attributes make 2D vdW multiferroic heterostructures, the hetero-stacks of ferroelectric and ferromagnetic layers, a promising pathway to realize efficient, non-volatile electrical control of 2D magnetism. Motivated by this, this dissertation focuses on experimentally probing the magnetoelectric effects in 2D multiferroic heterostructures. We initially demonstrate non-volatile ferroelectric modulation of magnetic properties in hybrid multiferroic heterostructures composed of 2D magnet Cr2Ge2Te6 and a ferroelectric polymer. By applying small voltages, we achieve reversible switching between two contrasting magnetic properties (i.e., named “ON” and “OFF” states), identifying polarization-dependent interfacial hybridization as the primary driving mechanism. To further improve interface quality and scalability, we replace the polymer ferroelectric with a 2D vdW ferroelectric and fabricate Fe3GeTe2/CuCrP2S6 all-vdW multiferroic heterostructures, which likewise exhibit low-voltage and non-volatile electrical control of 2D magnetism. Furthermore, we quantify the increasing control efficiency with the decreasing thickness of 2D magnets in heterostructures, which highlights that the short-range interfacial interaction dominates the magnetoelectric coupling in 2D multiferroic heterostructures. Collectively, this work contributes to the development and understanding of emerging 2D vdW multiferroic heterostructures by demonstrating the small-voltage non-volatile ferroelectric control of 2D magnetism, which holds technological implications for ultracompact, energy-efficient spintronic devices.