Universal theory of spin-momentum-orbital-site locking

Spin textures, i.e., the distribution of spin polarization vectors in reciprocal space, exhibit diverse patterns determined by symmetry constraints, resulting in a variety of spintronic phenomena. Here, we propose a universal theory to comprehensively describe the nature of spin textures by incorporating three symmetry flavors of reciprocal wavevector, atomic orbital and atomic site. Such approach enables us to establish a complete classification of spin textures constrained by the little co-group and predict unprecedentedly reported spin texture types, such as Zeeman-type spin splitting in antiferromagnets and quadratic spin texture. To examine the impact of atomic orbitals and sites, we predict orbital-dependent spin texture and anisotropic spin-momentum-site locking effects and corresponding material candidates validated through first-principles calculations. Our theory not only covers all possible spin textures in crystal solids described by magnetic space groups, but also introduces new possibilities for designing innovative spin textures by the coupling of multiple degrees of freedom

Reversible, electric-field induced magneto-tonic control of magnetism in mesoporous cobalt ferrite thin films

The magnetic properties of mesoporous cobalt ferrite films can be largely tuned by the application of an electric field using a liquid dielectric electrolyte. By applying a negative voltage, the cobalt ferrite becomes reduced, leading to an increase in saturation magnetization of 15% (M) and reduction in coercivity (H) between 5-28%, depending on the voltage applied (−10 V to −50 V). These changes are mainly non-volatile so after removal of −10 V M remains 12% higher (and H 5% smaller) than the pristine sample. All changes can then be reversed with a positive voltage to recover the initial properties even after the application of −50 V. Similar studies were done on analogous films without induced porosity and the effects were much smaller, underscoring the importance of nanoporosity in our system. The different mechanisms possibly responsible for the observed effects are discussed and we conclude that our observations are compatible with voltage-driven oxygen migration (i.e., the magneto-ionic effect)

Fundamental Properties of the Molecular Au Clusters

Monolayer-protected gold clusters (MPCs) are a very interesting and fascinating class of compounds, from the points of view of both the fundamental science and their possible applications. They are composed of a gold core, with a diameter smaller than a few nanometers, and are surrounded by a protecting organo-thiolate monolayer, bonded by covalent Au-S bonds. Due to their dimensions, these systems exhibit properties in between those of molecules and nanoparticles, therefore displaying unique physical and chemical behaviors. In this Thesis, some properties of the most stable and well-known molecular MPC are addressed and studied. The investigation focuses on fundamental features, including solid-state properties, optical behavior, reactivity and especially their magnetic properties. The investigation of the latter constitutes the major part of this work. Particular attention is dedicated to the effect of ligands on these phenomena. The main tool of our investigation was electron paramagnetic resonance (EPR) spectroscopy, which was used to study these MPCs both in solution and in the solid state. The topics addressed are to understand the magnetic interactions between gold core and the capping ligands in solutions phase and ferromagnetic and antiferromagnetic interactions between clusters in the solid state. Another magnetic resonance technique, nuclear magnetic resonance, was used for the study of the ligand exchange kinetics. The data obtained from a number of experimental techniques and computational calculations were used in conjunction with these two main tools