Polarized Neutron Diffraction Study on UPt_2Si_2

We investigated the magnetic structure of the antiferromagnetic (AFM) ordered state (T_ N∼ 34 K) in tetragonal UPt_2Si_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 ∼ 320 K. The modulation is characterized by a transverse wave in the c-plane, with the propagation vector of the CDW order, q_ CDW = (∼0.42, 0, 0). In the present study using neutron scattering, we observed that the superlattice reflections specified by q_ CDW develop below T_ 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) μ_ 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^∘ in the AFM state. The observations strongly suggest that the magnetism of UPt_2Si_2 is heavily influenced by the hybridization effects between 5f electrons of U and 5d electrons of Pt.