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 Cs₃Zn_0.9Co_0.1Cl₅. 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.