Manipulating chiral-spin transport with ferroelectric polarization

A collective excitation of the spin structure in a magnetic insulator can transmit spin-angular momentum with negligible dissipation. This quantum of a spin wave, introduced more than nine decades ago, has always been manipulated through magnetic dipoles, (i.e., timereversal symmetry). Here, we report the experimental observation of chiral-spin transport in multiferroic BiFeO3, where the spin transport is controlled by reversing the ferroelectric polarization (i.e., spatial inversion symmetry). The ferroelectrically controlled magnons produce an unprecedented ratio of up to 18% rectification at room temperature. The spin torque that the magnons in BiFeO3 carry can be used to efficiently switch the magnetization of adja-cent magnets, with a spin-torque efficiency being comparable to the spin Hall effect in heavy metals. Utilizing such a controllable magnon generation and transmission in BiFeO3, an alloxide, energy-scalable logic is demonstrated composed of spin-orbit injection, detection, and magnetoelectric control. This observation opens a new chapter of multiferroic magnons and paves an alternative pathway towards low-dissipation nanoelectronics

Computational Design of Multifunctional Nanodielectrics

In this dissertation, a mesoscale modeling approach is developed aimed at simulating the properties of dielectric nano/microstructures with coupled polar, elastic, and thermal degrees of freedom, as well as the dependence of these properties on the structure size, shape, morphology and applied conditions. The versatility of this computational method to predict functional behavior is exemplified in the following systems: (i) Semiconducting core-shell nanoparticles and the influence of their size, anisotropy, microstructure and applied pressure on their optical properties; (ii) Ferroelectric nanoparticles embedded in a dielectric medium, and the dependence on their polarization-field topology and transitions on particle shape and size, dielectric medium strength, applied electric field, as well as other factors; (iii) Artificial layered-oxide material exhibiting polar Goldstone-like (or phason) ex- citations and its electrocaloric properties that are tuneable under a wide range of applied conditions. The results of these investigations highlight the great promise of functional nano/mi- crostructures for a variety of advanced engineering applications, including electrothermal energy conversion, non-volatile multibit memories, opto and low-power electronics, as well as metamaterials by design. They also detail the utility of mesoscale control dials, I.e., manipulation of size, shape and microstructure, for fine-tuning the useful properties and operational response of functional nano/microstructures. Finally, we demonstrate that the development of predictive-grade mesoscale-level simulation techniques that accurately un- derpin complex physical phenomena occurring at this length scale is paramount for deeper understanding of the behavior of functional dielectrics and other materials