Band versus localized electron magnetism in ${\text{CaCrO}}_3$

The results of the calculation of the electronic and magnetic properties of the perovskite ${\text{CaCrO}}_3$ in the local spin-density approximation (LSDA) and local spin-density with the account of on-site Coulomb correlations $\left(\text{LSDA}+U\right)$ approximations are presented. Both approaches provide correct magnetic ground state [$C$-type antiferromagnet ($\text{AFM-}C$)], but electronic structure is rather different: metallic in LSDA and insulating in $\text{LSDA}+U$. The character of magnetic interactions and the mechanism of stabilization of the AFM-$C$ structure are also qualitatively different: if in LSDA it is a Stoner-like band magnetism with a rather strong next-nearest-neighbor (“diagonal”) exchange, in $\text{LSDA}+U$ it is due to a superexchange interaction of localized electrons with an orbital ordering thereof. As one can conclude from both theoretical and experimental results, apparently ${\text{CaCrO}}_3$ is in a crossover regime between localized and itinerant electrons.

Figure 1

(Color online) Total and $\mathrm{Cr}\text{−}3d$ DOSs obtained in LSDA calculations for the AFM-$C$ type of magnetic ordering. $\mathrm{Cr}\text{−}3d$ DOSs are presented for two spins: up (down) panel corresponds to spin majority (minority). Total DOS is shown summed over spins. The Fermi energy is at zero.

Figure 2

(Color online) Results of $\text{LSDA}+U$ calculations for AFM-$C$ type of magnetic ordering. (a) Comparison between total DOSs obtained with the use of full set of symmetry operations of $Pbnm$ group (blue dashed line) and with the symmetry constrains lifted, i.e., the symmetry-unrestricted solution (black solid line). Note that the plot is presented in the absolute scale; the position of the Fermi energy is indicated by dotted line. (b) Total (solid line) and partial (dashed and dash-dotted lines) DOSs for the symmetry-unrestricted solution. $\mathrm{Cr}\text{−}3d$ DOS are presented for two spins: up (down) panel corresponds to spin majority (minority). Total and $\text{O-}2p$ partial DOSs are shown summed over spins. The Fermi energy is at zero.

Figure 3

(Color online) Orbital structure (two orbitals on which electrons are localized) obtained in symmetry-unrestricted solution in $\text{LSDA}+U$ calculation for ${\text{CaCrO}}_3$ for AFM-C type of magnetic order. (a) One electron occupies the orbital with mostly $xy$ character, while (b) another, alternating $xz+yz/xz-yz$ orbitals. Local coordination system is shown. Atoms of oxygen are shown as balls.