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Description
The combination of nuclear forward scattering as time-domain synchrotron-based nuclear resonant scattering method with high-purity polarimetry is a novel approach to probe electronic anisotropies in metal-containing compounds ranging from biological molecules to solid state systems.
This method is based on exploring the polarization dependence of the nuclear hyperfine transitions at the 14.4 keV nuclear resonance of 57Fe. The use of a crossed polarizer-analyzer setup [1] allows the suppression of the incident σ-polarized non-resonant photons. Probing thereby single crystals, the magnitude and orientation of the electric field gradient (EFG) at the Mössbauer nucleus produced by charge anisotropies is deliverable.
The application of this method is shown by means of the study of the monoclinic phase of the spin crossover (SCO) complex [Fe(PM-BiA)2(NCS)2] (1). Iron(II) SCO compounds can be switched reversibly from the low spin to the high spin state, e.g. by variation of temperature [2]. The presence of a strong EFG at the Mössbauer nucleus that leads to a pure electric hyperfine interaction was shown by density functional theory calculations and conventional Mössbauer experiments on a powder sample of 1. The realised nuclear resonance scattering polarimetry experiments on a single crystal of 1 have delivered information in terms of magnitude and orientation of the EFG.
[1] B. Marx et al., Phys. Rev. Letters 110, 254801 (2013)
[2] P. Gütlich et al., Angew. Chem. 106, 2109 (1994)
