Possible Half Metallic Antiferromagnet in a Hole-Doped Perovskite Cuprate Predicted By First-Principles Calculations

We formulate a scheme to realize a half metallic antiferromagnet (HMAFM), a material conductive in only one spin channel while exhibiting zero macroscopic magnetism, by doping carrier into a class of cuprates. The working rationale is exhibited as taking advantage of Hubbard repulsion of $d$ electrons of Cu atoms and the charge-transfer effect from the associated O ligand to fully polarize the spin of a doped carrier. Specifically, doping one hole into the insulating ferrimagnet ${\mathrm{Sr}}_8{\mathrm{CaRe}}_3{\mathrm{Cu}}_4{\mathrm{O}}_{24}$ by replacing one of the eight Sr atoms by one Rb atom is predicted to achieve a HMAFM, presumably with room-temperature operation. Since the working rationale is the strong correlations of electrons commonly encountered in cuprates, it is expected that the present findings can shed light on a new way to develop a HMAFM.

Figure 1

Schematic representation of the unit cell. (a) Parent material (space group: $Pm\mathrm{\text{−}}3m$). Two unit cells for $1/8$ replacement of Sr atoms by the Rb atom: (b) the lowest symmetric, and (c) the highest symmetric (space group: $R3m$). (d) The $1/4$ replacement. The Sr (blue), Rb (green), Ca (gray), Re (yellow), Cu (brown), and O (red) atoms are shown in colored spheres.

Figure 2

Total density of states. (a) Parent material (green) and $1/8$ replacement with blue (red) for the highest (lowest) symmetric structure of the unit cell in Figs. 1c, 1b. In order to exactly contrast with the results of parent material, hereafter the results for $1/8$ replacement refer to the unit cell defined as Fig. 1b unless noted otherwise. (b) Parent material (green) and $1/4$ replacement (red).

Figure 3

Isosurface of spin magnetization density at $\pm 0.07{\mu }_B{\AA }^{-3}$ [pink (blue) color: $+$ ($-$) sign]. Here Cu1 locates at the center; Cu2 at the face center; O2 between Cu1 and Cu2. (a) Parent material, (b) $1/8$ replacement, and (c) $1/4$ replacement.

Figure 4

Partial density of states (PDOS) for the $3d$ states at the Cu1 and Cu2 sites, and the $2p$ states at the O2 site. (a), (b), and (c), respectively, depict the cases of the parent material, the $1/8$ replacement, and the $1/4$ replacement. In (b) the O2 atoms close to the Rb atom are displayed. The other O2 atoms show the similar half metallic features in the PDOS. In (c) the degenerate lower Hubbard states of Cu1 and Cu2, and the associated hybridization of O2 are highlighted by the arrow marks.