Neutron scattering and muon spin relaxation measurements of the noncentrosymmetric antiferromagnet CeCoGe₃

The magnetic states of the noncentrosymmetric pressure-induced superconductor CeCoGe₃ have been studied with magnetic susceptibility, muon spin relaxation (μSR), single-crystal neutron diffraction, and inelastic neutron scattering (INS). CeCoGe₃ exhibits three magnetic phase transitions at T_N1=21,T_N2=12, and T_N3=8K. The presence of long-range magnetic order below T _N1 is revealed by the observation of oscillations of the asymmetry in the μSR spectra between 13 and 20 K and a sharp increase in the muon depolarization rate. Single-crystal neutron-diffraction measurements reveal magnetic Bragg peaks consistent with propagation vectors of k=(0,0,23) between T_N1 and T_N2,k=(0,0,58) between T_N2 and T _N3 and k=(0,0,12) below T_N3. An increase in intensity of the (110) reflection between T_N1 and T_N3 also indicates a ferromagnetic component in these phases. These measurements are consistent with an equal moment two-up two-down magnetic structure below T_N3 with a magnetic moment of 0.405(5)μ_B/Ce. Above T_N2, the results are consistent with an equal moment two-up one-down structure with a moment of 0.360(6)μ_B/Ce. INS studies reveal two crystal-electric-field (CEF) excitations at ∼19 and ∼27meV. From an analysis with a CEF model, the wave functions of the J=52 multiplet are evaluated along with a prediction for the magnitude and direction of the ground-state magnetic moment. Our model correctly predicts that the moments order along the c axis, but the observed magnetic moment of 0.405(5) μ_B is reduced compared to the predicted moment of 1.0μ_B. This is ascribed to hybridization between the localized Ce3⁺ f electrons and the conduction band. This suggests that CeCoGe₃ has a degree of hybridization between that of CeRhGe ₃ and the noncentrosymmetric superconductor CeRhSi₃.