Flower state micromagnetic structure in fine cylindrical particles

Abstract

The flower state micromagnetic structure is analyzed in detail for soft and hard types of cylindrical ferromagnetic particles by means of computer simulation. Wide ranges of particle sizes and aspect ratios are considered. An analytical description of a flower state pattern in a fine ferromagnetic particle is also given on the basis of a perturbation theory. It is shown that for a small particle of a non-ellipsoidal external shape a flower state arises due to excitation of the Brown's stationary nucleation modes against the background of a uniform magnetization. These modes are brought about by the nonuniform components of the demagnetizing field of a particle. The comparison of the numerical and analytical data for a cylinder shows that the first-order formulas of the perturbation theory fit quantitatively the flower state pattern transformation due to changing of the particle aspect ratio l for a soft type cylinder with radius R⩽0.3 R 0, where R 0 is the exchange length. For a hard type cylindrical particle the same approach is approximately valid over the whole ranges of R and l which have been investigated.