Magnetic structure and crystal field states of antiferromagnetic CeNiGe${}_3$: Neutron scattering and $\hat{I}¼$SR investigations

Abstract

We present the results of microscopic investigations of antiferromagnetic CeNiGe${}_3$, using neutron powder diffraction (NPD), inelastic neutron scattering (INS), and muon spin relaxation ($\hat{I}¼$SR) measurements. CeNiGe${}_3$ crystallizes in a centrosymmetric orthorhombic crystal structure (space group: $Cmmm$) and undergoes antiferromagnetic (AFM) ordering. The occurrence of long-range AFM ordering at $T_{\mathrm{N}}\approx 5.2$~K is confirmed by magnetic susceptibility, heat capacity, neutron diffraction, and $\hat{I}¼$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 Ce${}^{3+}$ ($J=5/2$) and determined the CEF parameters and ground state wavefunctions of CeNiGe${}_3$. Moreover, zero-field $\hat{I}¼$SR data for CeNiGe${}_3$ at $T<T_{\mathrm{N}}$ 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.

13 pages, 9 figures