Induced-Moment Weak Antiferromagnetism and Orbital Order on the Itinerant-Localized Duality Model with Nested Fermi Surface : A Possible Origin of Exotic Magnetism in URu2Si2

The weak antiferromagnetism of URu₂Si₂ is discussed on the basis of a duality model which takes into account salient features of both itinerant fermions and "localized" component of spin degrees of freedom. The problem is analyzed in the framework of induced-moment mechanism by taking a singlet-singlet crystal field scheme together with the nesting property of partial Fermi surface of itinerant fermions . It is shown that the extremely small ordered moment m of O(10⁻²×μB) can be compatible with the large specific-heat jump at the transition temperature TN. Analysis performed in the presence of external magnetic field shows that the field dependence of m in the limit T→ 0 and TN$ do not scale except very near the critical field B which is consistent with a recent observation by Mentink. It is also shown that the antiferromagnetic magnetic order gives rise to a tiny amount of antiferromagnetic orbital order of f-electrons.