Magnetic materials have their (spins) aligned over a macroscopic length scale. Alignment of the spins is typically driven by exchange interaction between neighboring spins. While at absolute zero ( T = 0 ) the alignment can always exist, thermal fluctuations misalign magnetic moments at temperatures above the Curie temperature ( T C ), causing a phase transition to a non-magnetic state. Whether T C is above the absolute zero depends heavily on the dimensions of the system.