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Figure 1
The Tanabe–Sugano diagram and orbital states for octahedral ([Dq\gt 0]) and tetrahedral ([Dq\lt 0]) crystalline electric field environments. The orbital degeneracy in an octahedral crystalline field results in a spin transition from a 4T1 (high spin – HS) state to a 2E (low spin – LS) state for large values of Dq. For negative values of Dq (tetrahedral environment), the orbital triplet is replaced by a singlet state (4A2) with [S = {3 \over 2}]. However, real systems display a coupling between this singlet ground state and the excited orbital triplet resulting in a ground-state orbital degeneracy. The diagram was calculated taking the Racah parameters B and C to be the free ion values of 0.12 and 0.56 eV, respectively (see Abragram & Bleaney, 1986BB1, for discussion and further definitions). This work is centred around the goal of discovering new [\textstyle S = {3\over 2}] Co2+ magnets based on a tetrahedral crystal field ([Dq\lt 0], left side of the plot).

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206
Volume 71| Part 1| January 2015| Pages 20-24
doi:10.1107/S2052520614024809
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