Long-range order of dipolar fluids

The general theory of the isotropic–ferromagnetic transition of dipolar hard sphere fluids is considered on the base of the formalism of the direct correlation function. The equation of the Lovett–Mou–Buff–Gubbins type, described the one-particle orientational distribution, is generalized on a case of long-range interparticle potential and ellipsoidal sample shape. The exact criterion of the isotropic–ferromagnetic transition is found as a result of bifurcation analysis. It is shown that the formalism reduces to all known approximations in partial cases. A new expression for the susceptibility is obtained analytically within the framework of the generalized mean-spherical approximation. It is demonstrated that the susceptibility diverges at appropriate values of short-range correlations. In this way, the decisive role of short-range correlations outside the core in the transition appearance is established whereas the long-range correlations are found to be of secondary importance. The qualitative estimations show that the short-range pair correlations in dipolar fluids are most likely antiferromagnetic in character so as the transition to ferromagnetic liquid becomes questionable.