Magnetic structure and crystal-field states of antiferromagnetic CeNiGe3: Neutron scattering and 𝜇⁢SR investigations

We present the results of microscopic investigations of antiferromagnetic CeNiGe3 using neutron powder diffraction (NPD), inelastic neutron scattering (INS), and muon spin relaxation (𝜇⁢SR) measurements. CeNiGe3 crystallizes in a centrosymmetric orthorhombic crystal structure (space group 𝐶⁢𝑚⁢𝑚⁢𝑚) and undergoes antiferromagnetic (AFM) ordering. The occurrence of long-range AFM ordering at 𝑇N≃5.2K is confirmed by magnetic susceptibility, heat capacity, neutron diffraction, and 𝜇⁢SR measurements. The NPD data characterize the AFM state with an incommensurate helical magnetic structure having a propagation vector k = (0, 0.41, 1/2). In addition, INS measurements at 10 K identified two crystal electric field (CEF) excitations at 9.17 meV and 18.42 meV. We analyzed the INS data using a CEF model for an orthorhombic environment of Ce3+ (𝐽=5/2) and determined the CEF parameters and ground state wave functions of CeNiGe3. Moreover, zero-field 𝜇⁢SR data for CeNiGe3 at 𝑇<𝑇N show long-range AFM ordering with three distinct oscillation frequencies corresponding to three different internal fields at the muon sites. The internal fields at the muon-stopping sites have been further investigated using density functional theory calculations.