Artificial spin ice was invented in 2006 by Peter Schiffer's group as a large-scale model of pyrochlore spin ice. Their system, an array of mesoscopic magnets with submicron dimensions, offered a way to observe the physics of ice rules at the level of individual, albeit large, spins. Today we have artificial magnetic arrays that follow the ice rules almost flawlessly, which makes them better ice models than their natural counterparts. We will highlight both similarities and differences between natural and artificial versions of spin ice. Large differences are expected in the dynamics of these systems. Mesoscopic spins easily transfer energy to internal degrees of freedom. Putting them in motion typically requires driving the system far from equilibrium. Thus, in some aspects, artificial spin ice is closer to granular matter and random magnets than to a regular magnetic solid.
