Magnetization Reversal Studies of Building Blocks of Square Artificial Spin Ice Probed by 2-DEG Based Micro-Hall Magnetometry

Abstract

In recent years, a great deal of interest has been attracted by the physics of designer materials called `Artificial Spin Ice' (ASI) systems [1-2]. One of the most promising aspects of ASI system is their high tunability of the array geometry, which has opened new avenues [2]. While most efforts have focused on study of array of artificial spin ice structures [3-4], little work has been done on understanding the switching behavior of individual nanoislands coupled by dipolar interactions in ASI systems [5-6]. These strong shape anisotropic nanomagnets exhibits Ising spin-like behavior and may get affected by the unintentional defects introduced during fabrication. Thus, it is essential to investigate how such defects modify the local magnetic behavior which in turn may play a significant role in the overall switching behavior of the corresponding nanostructures [7]. In this work, we have investigated the magnetization reversal of a special geometry of dipolar coupled system of Ti/Ni80Fe20/Al arranged in double square-ring geometry, which represents the building block of square ASI system. We employed two-dimensional electron gas (2-DEG) based micro-Hall magnetometry technique to measure the nanoislands’ stray field and study their switching behavior. Fig. 1(a) shows the SEM image of fabricated structure on top of GaAs/AlGaAs based Hall sensors. The changes in the Hall voltage reflect the changes in the magnetic state of the dipolarly coupled nanomagnets. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures (shown in Fig. 1(b)), their reversal processes undergo complex behavior. The results suggest that local irregularities may play critical role in defining the exact micromagnetic state of the otherwise single domain nanomagnets leading to complex switching behavior, which is discussed in this work.