  An ultra-fast quench is applied to binary mixtures of superparamagnetic
colloidal particles confined at a two-dimensional water-air interface by a
sudden increase of an external magnetic field. This quench realizes a virtually
instantaneous cooling which is impossible in molecular systems. Using
real-space experiments, the relaxation behavior after the quench is explored.
Local crystallites with triangular and square symmetry are formed on different
time scales and the correlation peak amplitude of the small particles evolves
nonmonotonically in time in agreement with Brownian dynamics computer
simulations.
