Multiple energy scales in mesospin systems: The vertex-frustrated Saint George lattice

Henry Stopfel,Björgvin Hjörvarsson,Aaron Stein,Unnar B Arnalds,Vassilios Kapaklis,Thomas P A Hase

doi:10.1103/physrevmaterials.5.114410

Henry Stopfel, Björgvin Hjörvarsson + Show 4 more

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https://doi.org/10.1103/physrevmaterials.5.114410

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Abstract

The interplay between topology and energy hierarchy plays a vital role in the collective magnetic order in artificial ferroic systems. Here we investigate, experimentally, the effect of having one or two activation energies of interacting Ising-like magnetic islands---mesospins---in thermalized, vertex-frustrated lattices. The thermally arrested magnetic states of the elements were determined using synchrotron-based magnetic microscopy after cooling the samples from temperatures above the Curie temperature of the material. Statistical analysis of the correlations between mesospins across several length scales reveals changes in the magnetic order, reflecting the amount of ground state plaquettes realized for a vertex-frustrated lattice. We show that the latter depends on the presence, or not, of different activation energies.

Highlights

Tailoring the field response of magnetic mesospins using a hierarchy of energy scales was originally demonstrated by Cowburn and Welland [1]
We have investigated a conditional arrangement of mesospins wherein the two short mesospins representing the long mesospin in the modified Saint George (mSG) lattice have to be ferromagnetically aligned to each other
The analysis of the results of this study indicate that the long mesospins act as ordering seeds, around which the short mesospins preferably align themselves, which is in agreement with previous studies of the Shakti lattice [26]

Summary

Introduction

Tailoring the field response of magnetic mesospins using a hierarchy of energy scales was originally demonstrated by Cowburn and Welland [1] In their case, the hierarchy was obtained from a distribution in the size and shape of small magnetic elements which facilitated the design of magnetic cellular automata, with potential uses in information processing and nonvolatile information storage [1,2,3]. In lattice architectures based on square artificial spin ice, the pairwise frustration is lifted by the different interaction strengths between parallel and perpendicular islands at the vertex level [7,16,17]. A different approach was proposed by Morrison et al [13], creating lattices where it is impossible to choose all vertices to be in their lowest energy configuration, due to topological constraints

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