Determination of the magnetic ground states in CeNMSb2 compounds with NM=Cu , Ag, Au

In the present work, we investigated the magnetic ground state of CeNMSb₂ NM (noble metal): Cu, Ag, and Au compounds using electronic-structure calculations while following a full-potential linearized-augmented-plane-wave method. Due to the lack of mirror symmetry about the ab plane, the two Ce atoms---which are located at crystallographically equivalent sites---in a unit cell should be treated inequivalently, and, as a consequence, a 112 supercell must be constructed to accommodate the antiferromagnetic (AFM) configuration. The magnetic configuration of the ground state of AFM CeAuSb₂ is that the magnetic moments of the two Ce atoms in a conventional unit cell are aligned ferromagnetically and those of an adjacent cell are aligned oppositely along the easy axis. The ground states, including ferromagnetic CeAgSb₂ and AFM CeCuSb₂, are understood in terms of the exchange interaction J of neighboring Ce atoms. Our results clearly confirm a recent experimental finding, in which, under an external magnetic field (30. 16em{0ex}T) along the c axis, a spin-density wave (SDW) with a wave vector (, , 12), where 0. 136, is observed in an AFM CeAuSb₂ compound. The Fermi surface (FS) on the ab plane exhibits nesting along the (110) direction. The nesting vector q= (, , 0) 4pt{0ex} (2/a), with 0. 13, is very similar to the experimental result aside from 12 along the c axis. We argue that the modulation along the c axis is attributed to the period doubling along the c axis due to the lack of mirror symmetry. Although our calculated generalized susceptibility (q) exhibits a pair of peaks along the (110) direction at 0. 06 and 0. 13, which are related to FS nesting, the peak at 0. 06 can hardly be observed in the experiment because of the negligible oscillator strengths of interband transitions at a low q value. This implies that the observed SDW can be attributed to strong Fermi-surface nesting.