Neutron scattering study on the crystal structure, magnetic ordering, and crystalline electric field excitations in an uranium metallic compound U3Pd20Si6

Systematic neutron scattering experiments were carried out in order to reve al the crystal and magnetic structure as well as the localized character of the uranium 5f electrons in a ternary metallic compound U3Pd20Si6, High-re solution neutron powder patterns were well described by the model calculati on assuming the R3Pd20X6 structure. We found the successive magnetic sublat tice ordering at the Neel temperature T-N = 19 K and the Curie temperature T-C = 2 K respectively. Below T-N = 19 K the uranium spins on 8c site showe d an antiferromagnetic order with the propagation vector Q = [111]. Meanwhi le uranium spins on 4a site remained paramagnetic down to T-C = 2 K and ord ered ferromagnetically below T-C. Inelastic scattering experiments revealed clear evidence for the crystalline electric field excitations at the excit ation energy of about 13 and 23 meV. We also found a strong magnetic excita tion at low energy about 3 meV. A quasi-elastic response was observed above T-N, while the inelastic excitation energy showed remarkable temperature d ependence below T-N. These behaviors involve that the observed low energy r esponse would be the antiferromagnetic spin wave excitation, consistent wit h the localized character of the 5f electrons. The existence of crystalline electric field and spin wave excitations indicates that U3Pd20Si6 is one o f a few example of the uranium intermetallics in which uranium 5f electrons have a localized character.