Magnetic Structure of Phase II in U ( Ru 0.96 Rh 0.04 ) 2 Si 2 Determined by Neutron Diffraction under Pulsed High Magnetic Fields

International audienceWe report neutron diffraction measurements on U(Ru0.96Rh0.04)2Si2 single crystal under pulsed high magnetic fields up to 30 T applied along the tetragonal c axis. The high-field experiments revealed that the field-induced phase II above 26 T corresponds to a commensurate up-up-down ferrimagnetic structure characterized by the wave vector q=(2/3,0,0) with the magnetic moments parallel to the c axis, which naturally explains the one-third magnetization plateau and the substantially changed Fermi surface in phase II. This a-axis modulated magnetic structure indicates that the phase II near the hidden order phase is closely related to the characteristic incommensurate magnetic fluctuations at Q1=(0.6,0,0) in the pure system URu2Si2, in contrast to the pressure-induced antiferromagnetic order at Q0=(1,0,0)