Voltage-controlled magnetic double-skyrmion states in magnetoelectric elliptical nanostructures by phase-field model

The magnetic skyrmions are promising candidates as information carriers for future energy-efficient spintronic devices (e.g. memory, sensor, logic). Moreover, manipulating elliptically distorted skyrmions can result in a variety of novel functions that differ from those of conventional circular skyrmions. Despite the tremendous prospects, achieving voltage-driven dynamics of the elliptically distorted skyrmions remains a key challenge. Here, we employ dynamical phase-field simulations that consider the strain-mediated magnetoelectric coupling to demonstrate electric field manipulates the dynamic behavior of the elliptically distorted skyrmions. This study finds that the elliptically distorted skyrmions can split into smaller-sized circular skyrmions and reversibly switch between the single domain - single skyrmion and single domain - double skyrmion on elliptical nano-islands. The stabilization of magnetic skyrmions and double skyrmions in multiferroic heterostructures essentially depends on the ratio of the major axis and the minor axis of the elliptical nono-islands. Intriguingly, the operation is nonvolatile and exhibits a multistate character. The temporal behavior of energy density variations during the evolution of magnetic domain structures indicates that the electric-field manipulation of skyrmions originates from the competition between elastic, demagnetization, and anisotropic energies. Our work shows that deterministic switching of multiple domain structures on elliptical nano-islands is achievable, indicating the morphology is a new degree of freedom for manipulating the voltage-driven dynamics of skyrmions, providing a novel avenue to develop magnetoelectric coupling-based memory devices, logic devices, sensor devices, etc., at the nanoscale. Impact statement: This research aims to construct a unique multi-state storage device as well as to indicate the morphology is a new degree of freedom for manipulating the voltage-driven dynamics of skyrmions, giving a fresh way to create nanoscale magnetoelectric coupling-based memory, logic, sensor, and other devices.