Electronic Structure Analysis of the Difference between Cs₂AgF₄ and Rb₂MnF₄ in Their Magnetic Properties and Single-Crystal Structure Determination of Rb₂MnF₄

The single-crystal structure of Rb₂MnF₄ was determined, and first principles electronic band structure calculations were carried out for Cs₂AgF₄ and Rb₂MnF₄. The intralayer spin exchange is calculated to be ferromagnetic in Cs₂AgF₄ but antiferromagnetic in Rb₂MnF₄, in agreement with experiments. Our analysis indicates that the ferromagnetism in Cs₂AgF₄ originates from the spin polarization of the doubly occupied d_x²-y² band, which is induced by the d_z²−p−d_x²-y² orbital interactions through the Ag−F−Ag bridges, and similar interactions are not effective in La₂CuO₄. The crystal structure of Rb₂MnF₄ is quite similar to that of K₂MnF₄, as expected. However, most Rb₂MnF₄ crystals consist of numerous very thin platelets that are slightly skewed and/or shifted with respect to each other.