Attaining the Ground State of Kagome Artificial Spin Ice via Ultrafast Site-Specific Laser Annealing

TL;DR

This paper introduces an ultrafast, site-specific laser annealing technique to reliably achieve the ground state in kagome artificial spin ice, enabling precise control of magnetic configurations without altering the nanostructure.

Contribution

The work demonstrates a novel, deterministic method for ground state attainment in kagome ASI using selective laser annealing based on sublattice-dependent optical absorption.

Findings

Nearly perfect long-range magnetic order achieved

Selective sublattice demagnetization confirmed by simulations

Method does not require geometric modifications

Abstract

Artificial spin ices (ASIs) provide a versatile platform to explore magnetic frustration and emergent phenomena. However, in kagome ASI, experimental access to the ground state remains elusive due to dynamical freezing. Here, we demonstrate a deterministic and rewritable approach to attain the ground state using ultrafast, site-selective laser annealing. By engineering sublattice-dependent optical absorption through selective capping of the nanomagnets with Cr or utilizing different nanomagnet thicknesses, we achieve selective partial demagnetization of one sublattice under a sub-coercive magnetic field, driving the system into the ground state in a single switching step. Magnetic force microscopy reveals nearly perfect long-range ordering, while heat-transfer simulations confirm the sublattice-selective excitation mechanism. This work establishes an ultrafast method to attain the kagome ASI ground state, which does not require a modification of the geometry of the ASI or the materials used for the individual nanomagnets. Beyond ground-state writing, this site-selective activation provides an important tool for controlling the magnetic states, which is important for applications such as reconfigurable magnonic crystals, neuromorphic computing and programmable nanomagnetic logic.