H. Spiering

Mössbauer spectra of the tetrakis-(1,8-naphthyridine) iron(II)perchlorate in external magnetic fields. Evidence of slow relaxation ln paramagnetic iron(II)

Abstract 57 Fe Mossbauer spectra of [FeL 4 ] (ClO 4 ) 2 where L = 1,8-naphthyridine have been measured at 4.2°K in external magnetic fields up to 55 kG parallel to the direction of the γ-rays. The spectra have been fitted in the spin hamiltonian approximation assuming an orbital singlet ground state of the 5 D multiplet of Fe 2+ . The fit of the spectra is not unique, yet the possible spin hamiltonian parameter sets found lead to a spin doublet ground state split by less than 1 cm −1 . The transition probabilities for spin-lattice relaxation have been calculated for those ground states. Orbach processes via excited spin hamiltonian states cannot be neglected. The results explain the fluctuations observed in the spectra in low external magnetic fields (10 kG). The spin hamiltonian parameters provide information on the orbital energy levels. Therefrom the reduction of the quadrupole splitting by spin—orbit coupling results to be small thus explaining the extremely large quadrupole splitting of 4.54 mm/sec.

The Hermitian intensity matrix of a multipole transition

TheL-pole transition is described by a Hermitian (2L+1)×(2L+1) matrix. The incoherent absorption process of the nuclei in a crystal allows to sum up the matrices of all transitions at the same energy. The result is an intensity matrix of the crystal. The evaluation of the polarisation state of dipole transitions dependent on the γ-direction can be done by very simple tensor equations.

Polarisation effects in Mössbauer absorption by powder samples in external magnetic fields

The polarisation dependence of the absorption cross section must generally be taken into account in calculating Mössbauer absorption spectra of powder samples if they are partly polarised by an external magnetic field. The dependence of the intensity of the absorption lines on the aboorber thickness with an external field ofHa=50 kG is shown in the case of the paramagnetic specimen Fe(ClO4)2·6H2O. The calculation procedure is described and the results are compared with the usual thickness corrections neglecting polarisation effects.

Polarization effects in Mössbauer absorption by the diamagnetic powder of sodium-nitroprusside in external magnetic fields

The Mössbauer spectra of the powder sample of sodium nitroprusside have been measured in external magnetic fields at 4.2 K. The dependence of the absorption on thickness of the absorber has been studied. The fits including the polarization of the absorber by means of the applied field and the calculations of the convolution integral without polarization effects have been compared by a least squares value x2. The asymmetry parameter η of the EFG is η(4.2 K)=0.20±0.05.

Evaluation of single crystal57Fe Mössbauer spectra of finite thickness by the intensity matrix method: FeCl2·4H2O

The calculation of the absorption cross section for a polarized single crystal absorber of finite thickness is described using an intensity matrix method. The method is applied to the dipole transition of the quadrupole split Mössbauer spectrum of FeCl2·4H2O. For thickness corrections a simple hyperbola function is stated which approximates the absorption area of thick absorbers of an effective thickness from 0.4–10 within less than 1 per cent.

Ligand field and hyperfine interaction of the [Fe(H2O)6]2+ complex in different compounds

A series of compounds all containing the ferrous hexaquo complex were investigated by Mössbauer spectroscopy at 4.2K and in magnetic fields up to 5T and far infrared techniques. The results are interpreted in terms of a T2g ligand field model for which normal distortions of the water octahedron are used as parameters. The ferrous hexaquo complex can be described in all compounds by the same covalency, spin-orbit coupling and hyperfine coupling constants.

The ligand field at the Fe(II) ion in siderite

Abstract So far siderite has been intensely studied by Raman, far infrared. Mossbauer spectroscopy, and magnetic susceptibility measurements. The present work adds a Mossbauer measurement on a well oriented powder sample in applied fields of 80 kG normal to the spin direction of the uniaxial antiferromagnet at 4.2 K. The spins move 7.1° ± 0.4° out of the three-fold axis. The data can be described within the ligand field theory of the 5 D state of Fe 2+ including an exchange interaction proportional to the expectation value of the spin S. The exchange interaction is anisotropic ( J 1 ≈ 3 J 1 ). Covalency effects are very small. The orbital momentum operator and the hyperfine constants are affected by covalency in the order of 1 per cent.