Ground State of Divalent Co Ions in Cs3CoCl5 and Cs3CoBr5

Abstract

The 4A2 ground state of tetrahedrally coordinated divalent cobalt ions in Cs3CoCl5 and Cs3CoBr5 is investigated with magnetic-susceptibility measurements and paramagnetic resonance in pulsed magnetic fields up to 90 kOe at frequencies in the 70- and 120-Gc/sec bands. The first excited state (4T2) which lies ∼3000 cm−1 above the ground state is studied optically on Cs3Zn0.9Co0.1Cl5. The sign of the splitting of the 4T2 state is opposite to that expected from the observed negative zero-field splitting of the ground state.