The magnetization ground states (MGSs) for a nanosized Co hollow sphere, with the outer radius, R < 50 nm, have been studied numerically by micromagnetic simulation using object oriented micromagnetic framework (OOMMF). In addition to the originally known single domain and vortex-curling states, a three dimensional "onion" state with a corresponding analytical expression is proposed and confirmed as one of the ground states. Two phase diagrams, one for a single crystalline and the other for a polycrystalline nanosphere, are obtained for the three MGSs. The result reveals that the magnetic anisotropy has a significant effect on the phase line in the diagrams. The finite temperature effect and the blocking properties of the nanosphere for the magnetization reversal are discussed.
@article{arxiv.0812.2527,
title = {Magnetization ground states and phase diagrams for a nano-sized Co hollow sphere : an onion-type magnetization state},
author = {Desheng Kong and Siming Wang and Chinping Chen},
journal= {arXiv preprint arXiv:0812.2527},
year = {2009}
}