@inproceedings{matthias2011closed,
title={Closed magnetic geodesics on $S^2$},
author={Matthias Schneider},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20160912071122598399870},
booktitle={Journal of Differential Geometry},
volume={87},
number={2},
pages={343-388},
year={2011},
}