Strain-driven reversible switching of Radial vortex in a bicomponent nanomagnet

Radial magnetic vortices, characterized by their topological stability and nanoscale dimensions, are considered to be highly promising information carriers in magnetic electronic devices. However, traditional methods of reversing the polarity of radial magnetic vortices, which rely on magnetic fields or spin-polarized currents, encounter significant energy consumption problems. To address this challenge, this study proposes a novel field-free control scheme based on multiferroic heterostructures, consisting of a bicomponent nanomagnet (Terfenol-D/Ni), a heavy metal layer, and a piezoelectric layer. The intrinsic symmetry-breaking property of this structure effectively disrupts the circular symmetry of the radial magnetic vortex, which can make voltage-driven polarity reversal through magnetoelectric coupling effects. MuMax3-based multifield coupling simulations of electro-mechanical-magnetic interactions show that when the ratio of the bicomponent materials <inline-formula><tex-math id="M8">\begin{document}$ d _ { \rm T D } : d _ { \rm Ni } = 1 : 2 $\end{document}</tex-math></inline-formula> and the interfacial Dzyaloshinskii-Moriya interaction (DMI) coefficient (<i>D</i>) is in a range of <inline-formula><tex-math id="M10">\begin{document}$ 1 . 2\; {\rm m J / m ^ { 2 } } < D < 1 . 9\; {\rm m J / m ^ {2}} $\end{document}</tex-math></inline-formula>, the system stably presents a radial magnetic vortex state. Within this DMI coefficient range, when the thickness of the bicomponent nanomagnet is less than 4 nm, an appropriate radius can be found to ensure that the ground state of the bicomponent nanomagnet is a radial magnetic vortex state. Particularly, when the thickness <i>t</i> = 1 nm, the radius of the bicomponent nanomagnet can remain in the radial magnetic vortex state in a range of 50 ± 10 nm. In addition, this study also verifies that square and elliptical bicomponent nanomagnets each have a ground state of radial magnetic vortex. When <inline-formula><tex-math id="M12">\begin{document}$ D = 1.7\;{\rm m J / m ^ {2}} $\end{document}</tex-math></inline-formula>, only a 90 mV voltage pulse is required to achieve polarity reversal of the bicomponent nanomagnet, with a total energy consumption per bit Etotal of 5.6 aJ, which is six orders of magnitude lower than that from the traditional methods (reaching the aJ level). Through the simulation of transient magnetization dynamics and the analysis of energy evolution, this study reveals the physical mechanism of polarity reversal of radial magnetic vortices in this bicomponent multiferroic heterostructure: The energy competition in the bimaterial system driven by strain leads to the reconfiguration of magnetic moments, achieving the polarity reversal with efficient and ultra-low energy consumption. This scheme provides a new path for on-chip integration of magnetic vortex memory and opens up a new paradigm for designing non-current-driven “electric write” magnetic storage devices, which has significant application value in the field of low-power spintronics.