Polarized Neutron Diffraction Study on UPt₂Si₂

We investigated the magnetic structure of the antiferromagnetic (AFM) ordered state (TN ∼ 34 K) in tetragonal UPt2Si2 using polarized and unpolarized neutron diffraction. Previous neutron scattering studies reported that this system possesses a simple AFM structure with a propagation vector, Q = 0, and the ordered magnetic moments aligned along the c-axis. By contrast, our latest resonant X-ray scattering (RXS) experiments have revealed that the magnetic structure is modulated by the charge-density-wave (CDW) order, which emerges in one of the two Pt atomic layers in the unit cell below ∼320 K. The modulation is characterized by a transverse wave in the c-plane, with the propagation vector of the CDW order, \(qCDW = ( {~} 0.42,0,0)\). In this study using neutron scattering, we observed that the superlattice reflections specified by qCDW develop below TN, in addition to the magnetic reflections with Q = 0, thereby further confirming the presence of modulation in the AFM structure of this system. From detailed analyses, we revealed that the amplitude of the transverse-wave magnetic modulation is 0.72(2) μB/U, which is quantitative information that can not be obtained through RXS experiments. This implies that the CDW drives the ordered magnetic moments to be tilted up to 20° in the AFM state. The observations strongly suggest that the magnetism of UPt2Si2 is heavily influenced by the hybridization effects between the 5f electrons of U and the 5d electrons of Pt.