부산대학교 도서관

Since in the non-equilibrium state the distributed intrinsic angular momentum of a material medium (i.e., that due to the internal degrees of freedom of the constitutent molecules) is not necessarily a function of the magnetic moment density, it is necessary to include it explicitly in the equations of irreversible thermodynamics. It is an extensive variable contributing to the specific internal energy increment over and above the usual electromagnetic term $({\bf E}\cdot d{\bf D}+{\bf H}\cdot d{\bf B})/\rho$. This gives rise to an additional term in the entropy production. As a consequence of the formalism here developed, magnetic relaxation, whenever a phenomenological description is possible, can be derived from irreversible thermodynamics. The phenomenological equation for the time rate of change of the intrinsic angular momentum density is a generalization of the Bloch equation of nuclear induction. Noting that in irreversible thermodynamics, irreversible processes are associated with conservation laws, the more general meaning of this work is that ``thermodynamics of irreversible processes is completed by the fact that a characteristic irreversible process is now associated also with the conservation law of angular momentum''.