Metamagnetism and crystal-field splitting in pseudohexagonal CeRh3Si2

CeRh3Si2 has been reported to exhibit metamagnetic transitions below 5 K, a giant crystal field splitting, and anisotropic magnetic properties from single crystal magnetization and heat capacity measurements. Here we report results of neutron and x-ray scattering studies of the magnetic structure and crystal-field excitations to further understand the magnetism of this compound. Inelastic neutron scattering and resonant inelastic x-ray scattering reveal a Jz = 1/2 ground state for Ce when considering the crystallographic a direction as quantization axis, thus explaining the anisotropy of the static susceptibility. Furthermore, we find a total splitting of 78 meV for the J = 5/2 multiplet. The neutron diffraction study in zero field reveals that, on cooling from the paramagnetic state, the system first orders at TN1 = 4.7 K in a longitudinal spin density wave with ordered Ce moments along the b axis (i.e., the [0 1 0] crystal direction) and an incommensurate propagation vector k = (0, 0.43, 0). Below the lower-temperature transition TN2 = 4.48 K, the propagation vector locks to the commensurate value k = (0, 0.5, 0), with a so-called lock-in transition. Our neutron diffraction study in applied magnetic field H II b axis shows a change in the commensurate propagation vector and development of a ferromagnetic component at H = 3 kOe, followed by a series of transitions before the fully field-induced ferromagnetic phase is reached at H = 7 kOe. This explains the nature of the steps previously reported in field-dependent magnetization measurements. A very similar behavior is also observed for the H II [0 1 1] crystal direction.