We have performed elastic neutron-scattering experiments on the heavy-electron compound ${\mathrm{URu}}_2{\mathrm{Si}}_2$ for pressure $P$ up to 2.8 GPa. We have found that the antiferromagnetic (100) Bragg reflection below $T_m\sim 17.5\mathrm{K}$ is strongly enhanced by applying pressure. For $P<\mathrm{}1.1\mathrm{GPa}$, the staggered moment ${\mu }_o$ at 1.4 K increases linearly from $\sim 0.017\left(3\right){\mu }_B$ to $\sim 0.25\left(2\right){\mu }_B$, while $T_m$ increases slightly at a rate $\sim 1\mathrm{K}/\mathrm{GPa}$, roughly following the transition temperature $T_o$ determined from macroscopic anomalies. We have also observed a sharp phase transition at $P_c\sim 1.5\mathrm{GPa}$, above which a 3D-Ising type of antiferromagnetic phase ( ${\mu }_o\sim 0.4{\mu }_B$) appears with a slightly reduced lattice constant.

• Received 6 July 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.5114