Structure and magnetic properties of (CdSe)9 doped with Mn atoms

The electronic and geometrical structures of the (CdSe)9 cluster doped with Mn atoms are studied using density functional theory with generalized gradient approximation. It is found that the Fermi coupling constants in the Mn-substituted CdnSemMnk clusters (k = 1 and 2) are very sensitive to the Mn nearest neighbors. Generally, Se neighbors decrease the intensity of the Fermi coupling constant, whereas Cd neighbors amplify it. It is found that the Fermi coupling constant computed for the case when a Mn atom substitutes for a Se atom is close to the experimental value. Mn atoms added to the (CdSe)9 cluster either stick to Se atoms from inside or push out Cd atoms and occupy their previous positions. The lowest total energy state of (CdSe)9Mn is ferromagnetic, the antiferromagnetic singlet state and the ferromagnetic state with the total spin of 5 of (CdSe)9Mn2 are nearly degenerate in total energy, and the lowest total energy state of (CdSe)9Mn3 is ferrimagnetic with the total spin of 2.5. An excited singlet state of (CdSe)9Mn3 is found to possess the largest in the absolute value Fermi coupling constant among all species considered.