Orientational dynamics in magnetic fluids under strong coupling of external and internal relaxations

For the geometry of crossed magnetic fields—one constant and one oscillating—a kinetic model for the field-induced birefringence of a ferrofluid, which allows for the internal and external magnetic relaxations in colloidal particles, is constructed. Using it to interpret the Argand diagrams, one gets an opportunity to analyze the effect of coherent relaxation: the case of exact coincidence of the diffusion rates of the particle magnetic moment.