Magnetization dynamics of weakly interacting sub-100 nm square artificial spin ices

TL;DR

This study investigates the magnetization dynamics of thermally active artificial spin ices, revealing how interaction strength influences relaxation behavior and dimensionality, with implications for understanding out-of-equilibrium magnetic systems.

Contribution

It provides new insights into the effect of interaction strength on magnetization relaxation and dimensionality reduction in square artificial spin ices, supported by experimental and simulation data.

Findings

Stronger coupling leads to faster relaxation.

Observed a negative correlation between blocking temperature and interaction strength.

Magnetization dynamics suggest a transition from 2D to 1D behavior.

Abstract

Artificial Spin Ice (ASI), consisting of a two dimensional array of nanoscale magnetic elements, provides a fascinating opportunity to observe the physics of out of equilibrium systems. Initial studies concentrated on the static, frozen state, whilst more recent studies have accessed the out-of-equilibrium dynamic, fluctuating state. This opens up exciting possibilities such as the observation of systems exploring their energy landscape through monopole quasiparticle creation, potentially leading to ASI magnetricity, and to directly observe unconventional phase transitions. In this work we have measured and analysed the magnetic relaxation of thermally active ASI systems by means of SQUID magnetometry. We have investigated the effect of the interaction strength on the magnetization dynamics at different temperatures in the range where the nanomagnets are thermally active and have observed that they follow an Arrhenius-type N\'eel-Brown behaviour. An unexpected negative correlation of the average blocking temperature with the interaction strength is also observed, which is supported by Monte Carlo simulations. The magnetization relaxation measurements show faster relaxation for more strongly coupled nanoelements with similar dimensions. The analysis of the stretching exponents obtained from the measurements suggest 1-D chain-like magnetization dynamics. This indicates that the nature of the interactions between nanoelements lowers the dimensionality of the ASI from 2-D to 1-D. Finally, we present a way to quantify the effective interaction energy of a square ASI system, and compare it to the interaction energy calculated from a simple dipole model and also to the magnetostatic energy computed with micromagnetic simulations.