Energy minimization and AC demagnetization in a nanomagnet array

TL;DR

This study investigates AC demagnetization in nanomagnet arrays, revealing that finer step protocols reduce energy but do not reach the ground state, resulting in a complex disordered magnetic state.

Contribution

It provides a detailed analysis of AC demagnetization in frustrated nanomagnet arrays and models the resulting disordered states using a maximum-entropy approach.

Findings

Net magnetization approaches zero with small step sizes.

Final magnetostatic energy decreases with finer steps but does not reach the ground state.

Disordered magnetic states are described by a maximum-entropy ensemble.

Abstract

We study AC demagnetization in frustrated arrays of single-domain ferromagnetic islands, exhaustively resolving every (Ising-like) magnetic degree of freedom in the systems. Although the net moment of the arrays is brought near zero by a protocol with sufficiently small step size, the final magnetostatic energy of the demagnetized array continues to decrease for finer-stepped protocols and does not extrapolate to the ground state energy. The resulting complex disordered magnetic state can be described by a maximum-entropy ensemble constrained to satisfy just nearest-neighbor correlations.