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

Abstract

The magnetic properties of a pressure induced noncentrosymmetric heavy-fermion superconductor CeIrGe${}_3$ have been investigated by muon spin relaxation ($\hat{I}¼$SR), powder neutron diffraction (ND) and inelastic neutron scattering (INS) techniques at ambient pressure. For completeness we have also measured the ac magnetic susceptibility $\ddot{I}{‡}_{\mathrm{ac}}(T)$, dc magnetic susceptibility $\ddot{I}‡(T)$, dc isothermal magnetization $M(H)$ and heat capacity $C_{\mathrm{p}}(T,H)$ down to 2 K. CeIrGe${}_3$ is known to exhibit pressure induced superconductivity ($T_{\mathrm{c}}\approx 1.5$ 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 $\ddot{I}{‡}_{\mathrm{ac}}(T)$ and $\ddot{I}‡(T)$ data show an additional anomaly near 6.2 K which is also captured in $C_{\mathrm{p}}(T)$ data. From $\ddot{I}{‡}_{\mathrm{ac}}(T)$, $\ddot{I}‡(T)$ and $C_{\mathrm{p}}(T)$ measurements we infer three antiferromagnetic transitions above 2 K at $T_{N1}=8.5$ K, $T_{N2}=6.0$ K and $T_{N3}=4.6$ K. Our $\hat{I}¼$SR study also confirms the presence of three transitions through the observation of one frequency for $T_{N2}<T\le T_{N1}$, two frequencies for $T_{N3}<T\le T_{N2}$ and three frequencies for $T\le T_{N3}$ 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 Ce${}^{3+}$.

13 pages, 16 figures, 1 table