Nonlinear field effects in magnetic systems

Abstract

We develop a statistical-mechanical theory to treat nonlinear effects of static magnetic fields on systems of spin-bearing particles, applicable to liquids and configurationally disordered systems (e.g., glasses) as well as to rigid-lattice systems. After setting forth the general formalism, given in terms of several alternative functional Taylor-series expansions for the one-particle distribution function, we derive some exact formal results for magnetostriction and saturation through second order in magnetic field $H$ and examine an approximation closely related to the usual hypernetted-chain approximation of liquid-state theory. We briefly investigate the critical behavior, expressed at the one-particle level, of this approximation and note that magnetostriction produces the possibility of a magnetic tricritical point, as well as a crossover from normal to anomalous saturation as the liquid-gas critical point of a magnetic liquid is approached.