NONEQUILIBRIUM ANTIFERROMAGNETIC STATE IN THE HEAVY ELECTRON COMPOUND URu_2Si_2

摘要

We have investigated the nature of the antiferromagnetic (AF) phase induced by uniaxial stress σ in URu_2Si_2, by performing elastic neutron scattering measurements up to 0.4 GPa. We have found that the AF Bragg-peak intensity shows a clear hysteresis loop with σ under the zero-stress cooling condition. The result strongly suggests that the σ-induced AF phase is metastable and separated from the coexisting "hidden ordered" phase by a first-order phase transition. We also present the analyses of the crystalline strain effects, and suggest that the c/a ratio plays an important role in the competition between these two phases.