Hysteresis multicycles in nanomagnet arrays

TL;DR

This paper predicts hysteretic multicycles in nanomagnet arrays through simulations, highlighting the role of disorder, anisotropy, and the differences between vector and scalar models in magnetic hysteresis.

Contribution

It introduces the prediction of hysteretic multicycles in nanomagnet arrays using realistic spin dynamics simulations, emphasizing the effects of disorder and anisotropy.

Findings

Multicycles occur with probability up to ~0.6 in certain parameter regions.

Larger and more anisotropic nanomagnets tend to exhibit more multicycles.

Vector LLG dynamics break spin and field inversion symmetry unlike scalar models.

Abstract

We predict two new physical effects in arrays of single-domain nanomagnets by performing simulations using a realistic model Hamiltonian and physical parameters. First, we find hysteretic multicycles for such nanomagnets. The simulation uses continuous spin dynamics through the Landau-Lifshitz-Gilbert (LLG) equation. In some regions of parameter space, the probability of finding a multicycle is as high as ~0.6. We find that systems with larger and more anisotropic nanomagnets tend to display more multicycles. This result demonstrates the importance of disorder and frustration for multicycle behavior. We also show that there is a fundamental difference between the more realistic vector LLG equation and scalar models of hysteresis, such as Ising models. In the latter case, spin and external field inversion symmetry is obeyed but in the former it is destroyed by the dynamics, with important experimental implications.