A lattice of magnetic spins flipping by the Metropolis rule. Cool it and domains align into a magnet; heat past the critical temperature (Tc ≈ 2.269) and order dissolves into noise. Ported from my undergrad computational-physics C/OpenGL coursework.
Magnetisation curve |M| vs temperature
Quench it from hot straight down to near-zero and the lattice can jam into stripes: domain walls it's gone too cold to remove.
Why this happensRight at Tc the lattice never settles: domains of every size churn endlessly and the |M| dot jitters instead of holding still.
What you're seeingWith no field, cooling from random freezes the lattice mostly-gold or mostly-dark, at random. Reset a few times and watch it choose.
The deeper idea