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-augmentedplane-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 x 1 x 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 (<= 3 T) along the c axis, a spin-density wave (SDW) with a wave vector (eta, eta, 21), where eta approximate to 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 = (zeta, zeta, 0) (2 pi /a), with zeta - 0.13, is very similar to the experimental result aside from 21 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 chi (q) exhibits a pair of peaks along the (110) direction at zeta - 0.06 and 0.13, which are related to FS nesting, the peak at zeta - 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.