Device Applications of Heterogeneously Integrated Strain-Switched Ferrimagnets/Topological Insulator/Piezoelectric Stacks
Supriyo Bandyopadhyay
TL;DR
The paper investigates heterogeneously integrated stacks of ferrimagnet/ferrimagnet-like materials on topological insulators, where strain controls magnetic anisotropy to modulate TI surface conduction through interfacial exchange coupling. By integrating a piezoelectric layer, gate voltages generate strain that continuously tunes the FM anisotropy, enabling both analog (transconductance amplifier) and fixed-bias (synapse) operation via modulation of the TI current. The work discusses device architectures, material choices, and the potential for low-power, high-speed operation, while outlining future work to quantify behavior through Landau-Lifshitz-Gilbert-Langevin dynamics and NEGF transport modeling. The framework aims to bring quantum materials into practical, energy-efficient electronics and neuromorphic computing applications.
Abstract
A family of ferrimagnets (CoV2O4, GdCo, TbCo) exhibits out-of-plane magnetic anisotropy when strained compressively and in-plane magnetic anisotropy when strained expansively (or vice versa). If such a ferrimagnetic thin film is placed on top of a topological insulator (TI) thin film and its magnetic anisotropy is modulated with strain, then interfacial exchange coupling between the ferrimagnet (FM) and the underlying TI will modulate the surface current flowing through the latter. If the strain is varied continuously, the current will also vary continuously and if the strain alternates in time, the current will also alternate with the frequency of the strain modulation, as long as the frequency is not so high that the period is smaller than the switching time of the FM. If the strain is generated with a gate voltage by integrating a piezoelectric underneath the FM/TI stack, then that can implement a transconductance amplifier or a synapse for neuromorphic computation.