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)mu B/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 degrees 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.