Title: Investigations of the EPR parameters for the tetrahedral [FeX₄]^- clusters in AgX (X=Cl, Br)
Author(s):

	B.-T. Song (Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, P.R.China ) ,
	S.-Y. Wu (Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, P.R.China ,ad2) ,
	M.-Q. Kuang (Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, P.R.China ) ,
	Z.-H. Zhang (Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, P.R.China )

The EPR parameters g factors and the superhyperfine parameters for the tetrahedral [FeX₄]^- clusters in AgX (X=Cl, Br) are theoretically investigated from the perturbation formulas of these parameters for a 3d⁵ ion under tetrahedra by considering both the crystal-field and charge transfer contributions.The related model parameters are quantitatively determined from the cluster approach in a uniform way. The g-shift Δg (=g-g_s, where g_s≈2.0023 is the spin only value) from the charge transfer contribution is opposite (positive) in sign and much larger in magnitude as compared with that from the crystal-field one. The importance of the charge transfer contribution increases rapidly with increasing the covalency and the spin-orbit coupling coefficient of the ligand and thus exhibits the order of AgCl<AgBr. The unpaired spin densities of the halogen ns, npσ and npπ orbitals are quantitatively determined from the related molecular orbital coefficients based on the cluster approach.

Key words: crystal-fields and spin Hamiltonians, electron paramagnetic resonance (EPR), Fe³⁺, AgX (X=Cl, Br)
PACS: 71.70.Ch, 74.25.Nf, 74.72.Bk

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