  We study four-dimensional interacting fermions in a strong magnetic field,
using the holographic Sakai-Sugimoto model of intersecting D4 and D8 branes in
the deconfined, chiral-symmetric parallel phase. We find that as the magnetic
field is varied, while staying in the parallel phase, the fermions exhibit a
first-order phase transition in which their magnetization jumps
discontinuously. Properties of this transition are consistent with a picture in
which some of the fermions jump to the lowest Landau level. Similarities to
known magnetic phase transitions are discussed.
