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 1×1×2 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 (30.16em0exT) along the c axis, a spin-density wave (SDW) with a wave vector (η,η,1/2), where η≈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=(ζ,ζ,0)4pt0ex(2π/a), with ζ~0.13, is very similar to the experimental result aside from 1/2 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 χ(q) exhibits a pair of peaks along the (110) direction at ζ~0.06 and 0.13, which are related to FS nesting, the peak at ζ~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.