  We study the phase diagram of the Ising-Kondo lattice with transverse
magnetic field as a possible model for the weak-moment heavy-fermion compound
URu2Si2, in terms of two low-lying f singlets in which the uranium moment is
coupled by on-site exchange to the conduction electron spins. In the mean-field
approximation for an extended range of parameters, we show that the conduction
electron magnetization responds logarithmically to f-moment formation, that the
ordered moment in the antiferromagnetic state is anomalously small, and that
the Neel temperature is of the order observed. The model gives a qualitatively
correct temperature-dependence, but not magnitude, of the specific heat. The
majority of the specific heat jump at the Neel temperature arises from the
formation of a spin gap in the conduction electron spectrum. We also discuss
the single-impurity version of the model and speculate on ways to increase the
specific heat coefficient. In the limits of small bandwidth and of small
Ising-Kondo coupling, we find that the model corresponds to anisotropic
Heisenberg and Hubbard models respectively.
