Energy minimization and ac demagnetization in a nanomagnet array.
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.
Ke
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Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Li
J
J
Nisoli
C
C
Lammert
Paul E
PE
McConville
W
W
Wang
R F
RF
Crespi
V H
VH
Schiffer
P
P