@article{10_4171_dm_123,
     author = {Frans Oort and Thomas Zink},
     title = {Families of $p$-divisible groups with constant {Newton} polygon},
     journal = {Documenta mathematica},
     pages = {183--201},
     year = {2002},
     volume = {7},
     doi = {10.4171/dm/123},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/dm/123/}
}