The Preisach model represents a ferromagnet as a distribution of bistable "hysterons" — each switching at its own coercive fields. Their superposition produces the macroscopic B-H hysteresis loop, with memory encoded in the Preisach plane.
Preisach plane: each point (α,β) is a hysteron switching up at H=α, down at H=β. Distribution ρ(α,β) encodes material memory. Area inside loop = energy loss per cycle.