One can relate the magnetic moment of a system to the free energy of that system. In a uniform magnetic field B, the free energy F can be related to the magnetic moment M of the system as d F = − − S d T − − M ⋅ ⋅ d B where S is the entropy of the system and T is the temperature. Therefore, the magnetic moment can also be defined in terms of the free energy of a system as m = − − ∂ ∂ F ∂ ∂ B | T .