Periodic structure of memory function in spintronics reservoir with feedback current

TL;DR

This paper investigates how feedback current influences the memory capacity of vortex dynamics in spintronic reservoirs, revealing periodic behavior linked to feedback delay times and pulse widths.

Contribution

It provides a theoretical analysis showing that feedback effects do not always enhance memory, highlighting the periodic dependence on feedback delay relative to pulse width.

Findings

Memory function peaks when delay time is not a multiple of pulse width.

Memory function remains small when delay time is a multiple of pulse width.

Periodic short-term memory capacity behavior due to feedback correlations.

Abstract

The role of the feedback effect on physical reservoir computing is studied theoretically by solving the vortex-core dynamics in a nanostructured ferromagnet. Although the spin-transfer torque due to the feedback current makes the vortex dynamics complex, it is clarified that the feedback effect does not always contribute to the enhancement of the memory function in a physical reservoir. The memory function, characterized by the correlation coefficient between the input data and the dynamical response of the vortex core, becomes large when the delay time of the feedback current is not an integral multiple of the pulse width. On the other hand, the memory function remains small when the delay time is an integral multiple of the pulse width. As a result, a periodic behavior for the short-term memory capacity is observed with respect to the delay time, the phenomenon of which can be attributed to correlations between the virtual neurons via the feedback current.