Tutorial QT06—Recent Developments on the Properties of Emergent Layered 2D Quantum Magnetic Materials and Heterostructures

In this tutorial, the participants will learn:

1. Utility of Artificial Intelligence (AI) Tools for the Discovery of Two-Dimensional Magnets
2. Collective excitations of 2D magnetism probed by magneto-Raman spectroscopy
3. The magnetic interactions that drive the behavior of layered magnets from the perspective of neutron scattering, and its capability to probe magnetic order and excitations.
4. The spectroscopic properties of complex chalcogenides under the pressure
5. The development of the field with a focus on key discoveries related to fundamental electrical, optical, and magnetic properties of various inorganic 2D materials that make them distinct from conventional bulk solids
6. The magnetometry based on the nitrogen-vacancy (NV) center in diamond relevant to the field of 2D magnetic materials

AI Tools for the Discovery of Two-Dimensional Magnets
Trevor David Rhone, Rensselaer Polytechnic Institute

This section will present an overview of low dimensional materials, models of how magnetic moments interact and a summary of key recent discoveries and developments in 2D magnets, as well as discuss the main types of magnetic devices, e.g. magnetic tunnel junctions, magnetoresistant lateral transport devices and spin waves in tunneling devices.

Collective Excitations in Two-Dimensional Magnetic Atomic Crystals and Moiré Superlattices Probed by Magneto-Raman Spectroscopy
Liuyan Zhao, University of Michigan

Two-dimensional (2D) magnetism has been long sought after since its theoretical investigations in the 1960s and 1970s. It is only very recently that 2D magnetism is realized in magnetic atomic crystals and further tailored in magnetic moiré superlattices. Due to the small sample sizes of atomic and moiré crystals, traditional diffraction-based techniques become extremely challenging, and advanced optical spectroscopy techniques turn out to be uniquely suitable for probing magnetic properties in 2D magnets—both static and dynamic ones. In this tutorial, we will focus on collective excitations of 2D magnetism probed by magneto-Raman spectroscopy. Using CrI3 atomic crystals as an example, we will discuss four types of collective excitations in it: phonon for lattice, magnetism-coupled phonon for static magnetic order, magnon for dynamic magnetic excitations and polaron for phonon-dressed excitons. Then applying such acquired knowledge into twisted double bilayer CrI3 moiré superlattices, we will reveal unexpected net magnetization and potentially noncollinear spin textures that are absent in the layered antiferromagnetic CrI3 bilayer and four-layer films.

Neutron Scattering Studies of Layered Magnets
Rob McQueeney, Iowa State University

The tutorial will examine the magnetic interactions that drive the behavior of layered magnets from the perspective of neutron scattering. The tutorial will cover the basics of neutron scattering and its capability to probe magnetic order and excitations.  Various high flux neutron sources will be described and different methods and techniques for probing magnetism with neutrons will be discussed. Finally, several illustrative examples of neutron scattering data in layered magnetic systems will be presented along with their interpretation using idealized models, such as the Heisenberg model.

Complex Chalcogenides Under Pressure
Janice Musfeldt, University of Tennessee

This talk will focus on the spectroscopic properties of complex chalcogenides in the MPS3 (M = Mn, Ni, Fe, V) and CrPS4 family of materials and how external stimuli such as pressure control the development of new states of matter and functionality. New properties and symmetry progressions, elusive states of matter, and the structure-property relations that can be unraveled in this class of materials will be discussed in terms of metal site substitution, the presence or absence of the P-P dimer as a structural unit, the size of the van der Waals gap and layer thicknesses, slab corrugation, chirality and prospects for intercalation.

2D Materials: Fundamentals and Future Outlook
Goki Eda, National University of Singapore

The past decade has seen a tremendous rise in 2D materials research, driven by the prospects of this new class of materials for fundamental science as well as technological applications. In the past few years, the family of 2D materials has grown rapidly with the aid of computational discovery while experimental techniques have matured to accelerate the research findings. With the vast amount of information available in the literature, it can be challenging to gauge the current status of the field and identify open questions. This tutorial will overview the development of the field with a focus on key discoveries related to fundamental electrical, optical and magnetic properties of various inorganic 2D materials that make them distinct from conventional bulk solids. We will further discuss materials preparation and characterization techniques that are often crucial for observing the phenomenon of interest. Specifically, we will examine how van der Waals heterostructures offer a route to disorder-free samples and observation of novel interface physical phenomena. We will end with a discussion on the future outlook of this field.

Probing 2D Magnetism with Nanoscale Quantum Magnetometry
Brian Zhou, Boston College

The rapid evolution of magnetic materials towards the atomically thin limit has pushed them outside the sensitivity of currently available commercial magnetometers. At the same time, the coherent control of quantum systems has enabled versatile, solid-state magnetic field sensors that can be miniaturized to the nanoscale. In this tutorial, I will highlight the convergence of these two frontiers by introducing how magnetometry based on the nitrogen-vacancy (NV) center in diamond can offer unique perspectives to the field of 2D magnetic materials. These single spin magnetometers are capable of nanoscale spatial resolution, quantitative measurement and operation over a relatively wide phase space. Scanning probes made from advanced diamond nanofabrication have now enabled the imaging of the layer-dependent static magnetization and domain structures in mono- and few-layer ferromagnets. In addition, I will explain our group’s recent efforts using dynamical decoupling pulse sequences to enhance the magnetic field sensitivity and dynamical range of NV magnetometry for 2D magnets. This development opens the characterization of dynamical magnetic properties, including ac susceptibility, for ultrathin materials beyond ferromagnets.