Strong Spin-Orbit Coupling
Abstract
Implanting Strong Spin-Orbit Coupling at Magnetoelectric Interfaces This proposal aims at exploiting the fundamental idea of introducing strong spin-orbit coupling (SOC) into interface-driven nanostructures by embedding unit-cell-thick layers of 5d transition metal oxides to boost direct magnetoelectric (ME) effects. The development of multiferroic composites have been relying on the native interface and boundary formed between the ferroelectric (FE) and ferromagnetic (FM) materials. However, the ME coupling strength through native interfaces is limited by the energy scales of SOC inherent in the parent materials and has to rely on indirect mechanism. This proposal targets the development of cultured interfaces where broken inversion symmetry is blended with the strong SOC of 5d-states delivered by ultrathin alien layers. The success of this approach could establish a new paradigm of designing and fabricating transductional nanomaterials that convert energy between electric and magnetic domains. We anticipate that the design and synthesis of primary prototype ME superlattices of 5d spin-orbital moments can be developed by synergistic first-principles calculations and nonequilibrium heteroepitaxial growth within one year. Initial characterizations of ME coupling will also be carried out to enable future optimizing iterations between designs and synthesis. Derived from the results, designs and growth for more complex prototype structures with multiple active FE/FM components will also be investigated. Energy conversion between the electric and magnetic domains requires mutual couplings of the charge and spin degrees of freedom. Phenomena dictating direct ME effects are interplays of polar charge displacements and modulations in spin polarization/orientation. The microscopic origin is SOC, a relativistic effect where the electron spin feels an effective magnetic field when orbiting within the electric field of the nucleus. Since orbitals are spatial charge distributions of electrons that compose crystal lattices, SOC enables spin responses to electric polarizations and vice versa. Unfortunately, most magnetic materials are nonpolar and/or have relatively weak SOC. Realizations of ME effects have thus been relying on indirect mechanism through the combination of piezoelectricity and magnetorestriction1. However, if an enhancement of SOC can be achieved in a polar environment, direct ME effects are expected to be boosted. This proposal targets at meshing strong SOC with broken inversion symmetry naturally afforded by interfacial structures, which could lead to strong and tunable ME interaction. Demonstration of this strategy will enable new architecture designs for multiferroic composite and, more broadly ME materials and devices for transducers with high sensitivity and compact structures. Moreover, the implantation of SOC will utilize materials that host 5d-states microscopically but without macroscopic ferroic order. This “soft” character renders these spin-orbit states high ME susceptibilities when combined with switchable ferroic components for transducing energies. This feature of the proposed strategy is connected with an emerging field that exploits passive materials, e.g. paramagnetic and paraelectric, to achieve novel functionalities.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 09, 2016
- Source ID
- HR00111610005
Entities
People
- Jian Liu
Organizations
- Defense Advanced Research Projects Agency
- University of Tennessee