Polarized Neutron Diffraction Study on UPt$_{2}$Si$_{2}$

We investigated the magnetic structure of the antiferromagnetic (AFM) ordered state ($T_{\rm N} \sim$ 34 K) in tetragonal UPt$_{2}$Si$_{2}$ 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 $\sim$ 320 K. The modulation is characterized by a transverse wave in the $c$-plane, with the propagation vector of the CDW order, $q_{\rm CDW } =$ ($\sim$0.42, 0, 0). In the present study using neutron scattering, we observed that the superlattice reflections specified by $q_{\rm CDW }$ develop below $T_{\rm N}$, 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 to be 0.72(2) $\mu_{\rm B}$/U, which is a piece of quantitative information that could not be obtained through the RXS experiments. This implies that the CDW drives the ordered magnetic moments to be tilted up to 20$^\circ$ in the AFM state. The observations strongly suggest that the magnetism of UPt$_{2}$Si$_{2}$ is heavily influenced by the hybridization effects between 5f electrons of U and 5d electrons of Pt.