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.
Cite
@article{arxiv.0806.3925,
title = {Energy minimization and AC demagnetization in a nanomagnet array},
author = {X. Ke and J. Li and C. Nisoli and Paul E. Lammert and W. McConville and R. F. Wang and V. H. Crespi and P. Schiffer},
journal= {arXiv preprint arXiv:0806.3925},
year = {2008}
}