Neutron Scattering Study on Competition between Hidden Order and Antiferromagnetism in U(Ru1-xRhx)2Si2 (x ≤0.05)

We have performed elastic and inelastic neutron scattering experiments on solid solutions of U(Ru 1- x Rh x ) 2 Si 2 with Ru-rich concentrations: x =0, 0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with increasing x , and correspondingly, the onset temperature T m (∼17.5 K at x =0) of weak antiferromagnetic (AF) Bragg reflection decreases. For x =0.04 and 0.05, no magnetic order is detected in the investigated temperature range down to 1.4 K. In the intermediate range, 0.02 ≤ x ≤0.03, we found that the AF Bragg reflection is strongly enhanced. At x =0.02, this enhancement takes place at ∼7.7 K (≡ T M ), which is significantly lower than T m (∼ 13.7 K). T M increases with increasing x , and seems to merge with T m at x =0.03. If the AF state is assumed to be homogeneous, the staggered moment µ o estimated at 1.4 K increases from 0.02(2) µ B /U ( x =0) to 0.24(1) µ B /U ( x =0.02). The behavior is similar to that observed under hydrostatic pressure (µ o increases to ∼0.25 µ B /U at 1.0 ...