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 nz of O(10(-2) x mu(B)) can be compatible with the large specific-heat jump at the transition temperature T-N. Analysis performed in the presence of external magnetic field shows that the field dependence of m in the limit T --> 0 and T-N do not scale except very near the critical field B-c which is consistent with a recent observation by Mentink et al. It is also shown that the antiferromagnetic magnetic order gives rise to a tiny amount of antiferromagnetic orbital order of f-electrons.