Effect of Metal−Ligand Bond Lengths on Superexchange Interactions in Jahn−Teller d4 Ion Systems: Spin Dimer Analysis of the Magnetic Structure of Marokite CaMn2O4

In marokite CaMn2O4, all six Mn−O bonds of each MnO6 octahedron are different because of the Jahn−Teller distortion so that every Mn3+ (d4) ion has six different superexchange interactions with its neighboring Mn3+ ions. The spin exchange interactions of CaMn2O4 were examined on the basis of spin dimer analysis to find what geometrical parameters of the Mn−O−Mn superexchange paths control the signs and strengths of their spin exchange interactions. Our work correctly describes the magnetic structure of CaMn2O4 observed from neutron powder diffraction measurements and shows that the antiferromagnetic interactions of the Mn−O−Mn paths depend primarily on the asymmetry and the Mn−O bond length of the Mn−O−Mn bridge, but not on the ∠Mn−O−Mn bond angle.