The display on the left represents a lattice of spins: up spins are red, down spins are white. The temperature T, in units of the exchange interaction J, is set well above the ordering temperature, and the initial arrangement of up and down spins is random. Click run and the Monte-Carlo program runs for many cycles of the simulation. The spin arrangement after each cycle is displayed on the left and the magnetization as a function of time, since the last reset is graphed on the right.
Grab the handle of the external field slider and watch the change in the spin configuration as you vary the field to both positive and negative values.
Return the field to zero and lower the temperature gradually to a value less than 2. What's going on?