  We propose a method to generate massive entanglement in a spinor
Bose-Einstein condensate from an initial product state through adiabatic sweep
of magnetic field across a quantum phase transition induced by competition
between the spin-dependent collision interaction and the quadratic Zeeman
effect. The generated many-body entanglement is characterized by the
experimentally measurable entanglement depth in the proximity of the Dicke
state. We show that the scheme is robust to practical noise and experimental
imperfection and under realistic conditions it is possible to generate genuine
entanglement for hundreds of atoms.
