Origin of the Structural and Magnetic Anomalies of the Layered Compound SrFeO2: A Density Functional Investigation

The structural and magnetic anomaly of the layered compound SrFeO₂ are examined by first-principles density functional calculations and Monte Carlo simulations. The down-spin Fe 3d electron occupies the d_z² level rather than the degenerate (d_xz, d_yz) levels, which explains the absence of a Jahn-Teller instability, the easy ab-plane magnetic anisotropy, and the observed three-dimensional (0.5, 0.5, 0.5) antiferromagnetic order. Monte Carlo simulations show that the strong interlayer spin exchange is essential for the high Néel temperature.