${\mathrm{CaCrO}}_3$: An Anomalous Antiferromagnetic Metallic Oxide

Combining infrared reflectivity, transport, susceptibility, and several diffraction techniques, we find compelling evidence that ${\mathrm{CaCrO}}_3$ is a rare case of a metallic and antiferromagnetic transition-metal oxide with a three-dimensional electronic structure. Local spin density approximation calculations correctly describe the metallic behavior as well as the anisotropic magnetic ordering pattern of $C$ type: The high Cr valence state induces via sizable $pd$ hybridization remarkably strong next-nearest-neighbor interactions stabilizing this ordering. The subtle balance of magnetic interactions gives rise to magnetoelastic coupling, explaining pronounced structural anomalies observed at the magnetic ordering transition.

Figure 1

(a) Orthorhombic lattice parameters $a$, $b$, and $c$, scaled to the parameter of a cubic perovskite: $a_{\mathrm{cub}}=a/\sqrt{2}$, $b_{\mathrm{cub}}=b/\sqrt{2}$ and $c_{\mathrm{cub}}=c/2$. (b) and (c) show the orthorhombic splitting $\epsilon$ and the lattice volume $V$. Circles refer to synchrotron and triangles to neutron diffraction results.

Figure 2

(a) Crystal structure of ${\mathrm{CaCrO}}_3$ in space group Pbnm and the $C$-type magnetic structure of Cr moments (red) indicating the main magnetic interaction paths. (b) Magnetic susceptibility. (c)–(h) Results of powder neutron (squares) and single-crystal x-ray (circles) measurements. (c) Magnetic $(010)/(100)$ reflection at 3.5 K and calculated profiles for $C_x$, $C_y$ and $C_z$ type magnetic order. (d) Part of the neutron diffraction pattern at 3.5 K and calculated profiles. (e) Ratio of O2-O2 and Cr-O2 bond lengths; (f) Octahedral tilt $\Theta$ and rotation $\Phi$ angles. (g) Cr-O1 and Cr-O2 bond lengths. (h) $C_y$-type ordered magnetic moment in ${\mu }_B$.

Figure 3

Reflectivity (top) and optical conductivity ${\sigma }_1(\omega )$ (bottom). The inset in the bottom panel shows ${\sigma }_1(\omega )$ at low frequencies on an enlarged scale; the inset in the top panel depicts the resistivity $\rho (T)$.