Electronic structure of Co^III doped bromo-bridged Ni complexes, [Ni_1-xCo_x(chxn)₂Br]Br₂

This article describes the electronic structure of the Co^III doped Br bridged Ni^III complexes, [Ni_1-xCo _x(chxn)₂Br]Br₂ (x = 0.01, 0.02, 0.05, and 0.11) by using a optical spectroscopy, scanning tunneling microscopy (STM), and electron spin resonance spectroscopy. In the optical reflectivity spectrum, the new band was formed at about 0.5 eV, which is reasonably recognized as the d_z2 band of doped Co^III ions. In the STM images of [Ni_1-xCo_x(chxn)₂Br]Br₂, the bright spots attributable to the tunnel current from the Fermi level of the STM tip to the conduction band of the sample were observed. In addition, some brighter spots were also observed. Because the number of the brighter spots is in good agreement with that of doped Co species, the brighter spots can be assigned to doped Co^III sites. These are reasonably explained by the tunnel current from the Fermi level of the tip to the d_z2 band of Co ^III. The Curie spin concentration was gradually increased with increasing Co^III ions, which is explained by the scissions of the S = 1/2 1D antiferromagnetic chains.