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We have performed elastic and inelastic neutron scattering experiments on the solid solutions U(Ru1−xRhx)2Si2 for the 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 Tm (∼ 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 middle range, 0.02 ≤ x ≤ 0.03, we found that the AF Bragg reflection is strongly enhanced. At x = 0.02, this takes place at ∼ 7.7 K (≡ TM), which is significantly lower than Tm (∼ 13.7 K). TM increases with increasing x, and seems to merge with Tm at x = 0.03. If the AF state is assumed to be homogeneous, the staggered moment µo estimated at 1.4 K increases from 0.02(2) µB/U (x = 0) to 0.24(1) µB/U (x = 0.02). The behavior is similar to that observed under hydrostatic pressure (µo increases to ∼ 0.25 µB/U at 1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an increase in the AF volume fraction. We also found that the magnetic excitation observed at Q = (1, 0, 0) below Tm disappears as T is lowered below TM.

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We have performed angle-resolved photoelectron spectroscopy experiments in the soft x-ray region in order to clarify the band structure and Fermi surfaces (FSs) of URu 2 Si 2 . In the vicinity of the Fermi level, U 5f -derived quasiparticle bands were clearly observed. They form a small and a large hole FS centered at the Z point and a large electron FS centered at the point. The overall band structure as well as the FSs are explained by a band structure calculation treating all U 5f electrons as being itinerant. The observed FSs have nesting vectors which give a possible explanation for the spin fluctuations observed by inelastic neutron scattering measurements.