Understanding the magnetism in noncentrosymmetric CeIrGe3: Muon spin relaxation and neutron scattering studies

The magnetic properties of a pressure induced noncentrosymmetric heavy-fermion superconductor CeIrGe3 have been investigated by muon spin relaxation (μSR), powder neutron diffraction (ND), and inelastic neutron scattering (INS) techniques at ambient pressure. For completeness we have also measured the ac magnetic susceptibility χac(T), dc magnetic susceptibility χ(T), dc isothermal magnetization M(H), and heat capacity Cp(T,H) down to 2 K. CeIrGe3 is known to exhibit pressure induced superconductivity (Tc≈1.5 K) at a pressure of 20 GPa and antiferromagnetic ordering at 8.7 K, 4.7 K, and 0.7 K at ambient pressure. Our χac(T) and χ(T) data show an additional anomaly near 6.2 K which is also captured in Cp(T) data. From χac(T), χ(T), and Cp(T) measurements we infer three antiferromagnetic transitions above 2 K at TN1=8.5 K, TN2=6.0 K, and TN3=4.6 K. Our μSR study also confirms the presence of three transitions through the observation of one frequency for TN2<T≤TN1, two frequencies for TN3<T≤TN2, and three frequencies for T≤TN3 in the oscillatory asymmetry. The ND data reveal an incommensurate nature of the magnetic ordering at T=7 K with the propagation vector k = (0,0,0.688(3)), and a commensurate magnetic structure at T=1.5 K with the propagation vector locked to the value k = (0, 0, 2/3) and magnetic moments oriented along the c axis. The commensurate structure couples a macroscopic ferromagnetic component, resulting in a strong dependence of the lock-in transition temperature on external magnetic field. The INS data show two well defined crystal electric field (CEF) excitations arising from the CEF-split Kramers doublet ground state of Ce3+. The CEF energy levels scheme and wave functions have been determined. The ND and INS results together suggest that the anisotropic magnetic exchange are playing an important role in the magnetism of CeIrGe3.