Orbital ordering in the two-dimensional ferromagnetic semiconductor Rb2CrCl4Rb2CrCl4

We present the results of electronic structure calculations for the two-dimensional ferromagnet Rb2CrCl4Rb2CrCl4. They are obtained by the augmented spherical wave (ASW) method as based on density functional theory and the local density approximation. In agreement with experimental data, Rb2CrCl4Rb2CrCl4 is found to be semiconducting and displays long-range ferromagnetic order of the localized Cr 3d moments. The magnetic properties are almost independent of the structural modifications arising from the Jahn–Teller instability, which leads from the parent body-centered tetragonal K2NiF4K2NiF4 structure to a side-centered orthorhombic lattice. In contrast, the insulating gap is observed only for the latter structure due to the reduced symmetry. Our results thus suggest to interpret the orbital ordering as a necessary prerequisite for the opening of the gap rather than for the ferromagnetic order.