Effect of pressure on tiny antiferromagnetic moment in the heavy-electron compound URu2Si2

We have performed elastic neutron-scattering experiments on the heavy-elect ron compound URu2Si2 for pressure P up to 2.8 GPa. We have found that the a ntiferromagnetic (100) Bragg reflection below T-m similar to 17.5 K is stro ngly enhanced by applying pressure. For P < 1.1 GPa, the staggered moment m u(0) at 1.4 K increases linearly from similar to 0.017(3)mu(B) to similar t o 0.25(2)mu(B), while T-m increases slightly at a rate similar to 1 K/GPa, roughly following the transition temperature T-0 determined from macroscopi c anomalies. We have also observed a sharp phase transition at P-0 similar to 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu(0) s imilar to 0.4 mu(B)) appears with a slightly reduced lattice constant.