Nanoseminar in Physics - IN PRESENCE EVENT - REGISTER HERE to attend

Speaker: Prof. Jordi Sort, Department of Physics, Universitat Autònoma de Barcelona, Bellaterra, Spain  

Abstract: Controlling magnetism with voltage has an enormous potential to boost energy efficiency in nanoscale magnetoelectric devices since the use of electric fields (instead of magnetic fields or electric currents) minimizes Joule heating effects and reduces the overall device power consumption. In recent years, we have demonstrated the possibility to induce reversible, non-volatile changes in the magnetic properties (coercivity, remanent magnetization and saturation magnetization) of nanoporous films consisting of metal alloys (e.g., CuNi, FeCu) or oxides (e.g., FeOx, CoFe2O4), by applying an electric field through a liquid electrolyte gate at room temperature [1,2]. In addition, we have made significant progress in the field of magneto-ionics (i.e., voltage-driven ion transport in magnetic materials), which has traditionally relied on controlled migration of oxygen or lithium ions. Here, I will show that voltage-driven transport of nitrogen ions can be also triggered at room temperature in transition metal nitride (CoN, FeN, CoMnN and CoFeN) films via liquid electrolyte gating [3,4]. Nitrogen magneto-ionics can induce reversible ON-OFF transitions of ferromagnetic states at faster rates and lower threshold voltages than oxygen magneto-ionics. This is due to the lower activation energy needed for ion diffusion and the lower electronegativity of nitrogen with cobalt, compared with oxygen. Remarkably, and in contrast to oxygen magneto-ionics, nitrogen transport occurs uniformly through a plane-wave-like migration front, without the assistance of diffusion channels, which is particularly interesting for the implementation of multi-stack memory devices. Furthermore, we will show that both oxygen and nitrogen magneto-ionics can be used to emulate some important neuromorphic/synaptic functionalities (spike amplitude-dependent plasticity, spike duration-dependent plasticity, long term potentiation/depression). By tuning ion cumulative effects of DC and pulsed voltage actuation (at frequencies in the range 1 – 100 Hz), learning, memory retention, forgetting and self-learning by maturity (post-stimulated learning) can be mimicked. The latter can serve as a logical function for the device to decide between self-learning or forgetting emulation, at will, post-voltage input. This constitutes a novel approach to emulate some specific neural functionalities (e.g., learning under deep sleep), that are challenging to achieve using other classes of materials currently employed for neuromorphic computing applications.

References:

[1] A. Quintana et al., Adv. Funct. Mater. 27 (2017) 1701904. [2] C. Navarro-Senent et al., APL Mater. 7 (2019) 030701. [3] J. de Rojas et al., Nat. Commun. 11 (2020) 5871. [4] J. de Rojas et al, ACS Appl. Mater. Interfaces 13 (2021) 30826–30834. [5] Z. Tan et al., Mater. Horiz. 10 (2023) 88–96.

Hosted by Prof. Javier Rodríguez Viejo, Thermal Properties of Nanoscale Materials Group Leader.

A coffee service will be available at the room for attendees.