Crystal structure, magnetic ordering, and magnetic excitation in the 4f-localized ferromagnet CeAgSb₂

Systematic neutron-scattering experiments have been carried out in order to reveal the crystal and magnetic structures as well as the magnetic excitation in the Ce-based intermetallic compound CeAgSb₂. It was clarified that the Ag atoms in CeAgSb₂(space group: P4/nmm) occupy the 2b site, while Sb atoms occupy 2a and 2c sites, which have, to date, been controversial in literature. From the analysis of neutron powder-diffraction profile, we found the existence of the ferromagnetic component of about 0.41μ_B/Ce oriented along the c axis, consistent with the result of previous studies. On the other hand, however, no trace of the antiferromagnetic or spin-density wave peak was detected within our range of experimental accuracy. We observed a considerable spin-wave excitation below 3 meV. The dispersion relation was explained by the anisotropic Heisenberg model. This means that CeAgSb₂ has a simple ferromagnetic structure. Furthermore, crystalline electric-field (CEF) excitations were observed at 5.2 and 12.5 meV in the paramagnetic state, which is indicative of the localized nature of the Ce-4f electron. Our analysis revealed that formul presented is the ground state, while the first and second excited levels are mainly due to formul presented, respectively. The observed ferromagnetic moment is in good agreement with the ground-state saturation moment, g_Jμ_BJ_z∼0.43μ_B. The susceptibility, magnetization curve, and magnetostriction can be explained in terms of the CEF level scheme with anisotropic exchange interaction.