Sinusoidally modulated magnetic structure of a kondo lattice compound CePd₅Al₂

The magnetic structure of CePd₅Al₂, crystallizing in the tetragonal ZrNi₂Al₅-type structure, was studied by neutron diffraction technique using single crystals. This compound exhibits antiferromagnetic (AF) orderings at T_N1 = 4.1 K and T_N2 = 2.9 K. Below T_N1 magnetic peaks were observed at Q = (0.235, 0.235, 0) and its equivalent positions. Our analysis of the Q-dependence of the peak intensities suggests a sinusoidally modulated magnetic structure where the magnetic moments of 2.0(1) μ_B/Ce align along the c-axis. Third-order harmonics were also observed at temperatures from 3 K to 0.8 K, suggesting that the magnetic moments square up in the ground state. Inelastic neutron scattering measurements revealed well-defined crystalline electric field (CEF) excitations at 21.3 and 22.4 meV. The derived wave functions of the CEF ground state consist primarily of |±5/2>, which reproduce the anisotropic behavior of the magnetic susceptibility and isothermal magnetization in the paramagnetic state.