Round 11: Tossup 15
At low temperature, this quantity equals its value at absolute zero times the expression “1 minus temperature over critical temperature raised to the three-halves power.” Between Bloch domains, this vector rotates continuously about the normal of the Bloch wall plane. The volume bound current density equals the curl of this quantity. This quantity is the order parameter of the Ising model, in which it spontaneously emerges as temperature is decreased in a phase transition. The H-field equals the B-field divided by the permeability of free space minus this quantity. When increasing the applied field no longer increases this quantity, a ferromagnet has become saturated. For 10 points, name this vector defined as the magnetic dipole moment per unit volume, the magnetic analog of electric polarization. ■END■