Magnetic structure and crystal-field states of antiferromagnetic CeNiGe3: Neutron scattering and μsR investigations

We present the results of microscopic investigations of antiferromagnetic CeNiGe3 using neutron powder diffraction (NPD), inelastic neutron scattering (INS), and muon spin relaxation (μSR) measurements. CeNiGe3 crystallizes in a centrosymmetric orthorhombic crystal structure (space group Cmmm) 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 μSR 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 μSR 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.