Magnetic structure of phase II in U(Ru_0.96Rh_0.04)₂Si₂ determined by neutron diffraction under pulsed high magnetic fields

K. Kuwahara, S. Yoshii, H. Nojiri, D. Aoki, W. Knafo, F. Duc, X. Fabrèges, G. W. Scheerer, P. Frings, G. L. J. A. Rikken, F. Bourdarot, L. P. Regnault, and J. Flouquet

Accepted Thursday May 2, 2013

We report neutron diffraction measurements on {\urrs} 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 ${\bm q} = (2/3,0,0)$ with the magnetic moments parallel to the $c$-axis, which naturally explains the one-third magnetization plateau \color{blue} 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 ${\bf Q}_1 = (0.6,0,0)$ in the pure system {\urs}, in contrast to the pressure-induced antiferromagnetic order at ${\bf Q}_0 = (1,0,0)$. \color{black}