In-field Mossbauer spectroscopy

Schematic representations of (a) parallel and (b) perpendicular measuring geometry, most frequently used In in-field Mossbauer spectroscopy.

Elucidation of Bulk Magnetic Properties in Nanoferrites Using In-Field Mossbauer Spectroscopy... 

The third prominent interaction in iron Mossbauer spectroscopy is the magnetic hyperfine interaction of the Fe nucleus with a local magnetic field. As explained in detail in Chap. 4, it can be probed by performing the Mossbauer experiment in the presence of an applied external magnetic field. 

Four-coordinate, planar iron(II)-dithiolate complexes also exhibit intermediate spin. The first example described was the tetraphenylarsonium salt of the square-planar bis(benzene-l,2-dithiolate)iron(II) dianion, (AsPh4)2[Fe(II)bdt2], which showed 5 = 0.44 mm s and AEq = 1.16 mm s at 4.2 K [157]. The electronic structure of a different salt was explored in depth by DFT calculations, magnetic susceptibility, MCD measurements, far-infra red spectroscopy and applied-field Mossbauer spectroscopy [158]. 

Previous attempts to distinguish between the different kinds of pairs by applying microscopic methods such as conventional Mossbauer spectroscopy were unsatisfactory, since the Mossbauer spectra corresponding to the HS state of the iron(II) atoms in the [HS-LS] and [HS-HS] spin pairs are indistinguishable. Zero-field Mossbauer spectroscopy applied to the bpym-bridged iron(II) dinuclear compounds only gives access to the total fraction... 

Although relatively little used in catalysis, Mossbauer spectroscopy has given important information on the state of iron and cobalt in Fischer-Tropsch and hydrodesulphurization catalysts. Mossbauer spectroscopy provides the oxidation state, the magnetic field and the lattice symmetry of a number of elements such as iron, tin, iridium, and cobalt, and can be applied in situ. We will first describe the theory behind the Mossbauer effect and explain how a nuclear technique gives information on the state of atoms. 

At this point, if we consider the Mossbauer parameters calculated in conventional Mossbauer spectroscopy, the isomer shift (IS) is not accessible from NFS spectra, because the latter only shows interference between radiation fields corresponding to different radiations. Isomer shifts will have to be measured relative to a second reference absorber that must be placed behind or in front of the sample along the y-ray beam. 

The Fe complex of 4,6-di-ter butyl-2-aminothiophenol has been characterized crystallographically with the ligand in o-aminothiophenolate(l-), aromatic o-iminothiophenolate dianionic (2 ) and open-shell o-iminothionebenzosemiquino-nate (1-) forms. Zero-field Mossbauer spectroscopy unambiguously confirms the presence of high-spin ferrous ions throughout. ... 

W.R. Dunham, et al., 2-Iron ferredoxins in spinach, parsley, pig adrenal cortex, Azotobacter vinelandii, and Clostridium pasteur-ianum—studies by magnetic field Mossbauer spectroscopy. 2, Biochim. Biophys. Acta 1971, 253(1), 134. 

If an external magnetic field is applied to a sample and a transmission Mossbauer spectrum is recorded, we get an in-field Mossbauer spectrum. The combination of transmission Mossbauer spectroscopy and external magnetic field is then referred to as in-field (or high-field) Mossbauer spectroscopy [88-94]. 

Thus, Mossbauer spectroscopy in combination with external magnetic fields provides a complex physicochemical characterization of studied nanosized iron(lll) oxides since it enables (i) more precise determination of phase compositions (ii) fitting zero-field Mossbauer spectra on the basis of phase analysis obtained from in-field Mossbauer spectra (Hi) separation of individual contributions from various crystallographic sites (iv) determination of direction of Beff and magnetic moments of Fe " " ions in iron(lll) oxides and (v) study of spin-canting phenomenon and determination of various spin noncollinearities (e.g., spin frustration, spin-glass-like behavior, etc.). 

V. Ksenofontov, H. Spiering, S. Reiman, Y. Garcia, A.B. Gaspar, J.A. Real, P. Gutlich, Determination of spin state in dinuclear iron(II) coordination compounds using applied field Mossbauer spectroscopy. Hyperfine Interact. 141/142, 47-52 (2002)... 

There is not much doubt that the magnetic properties of the atoms near the surface are different from the properties of the atoms in the interior. The thermal evolution of the hyperfine field, and probably that of the recoilless fraction are faster than for the bulk atoms. This may influence the way in which Mossbauer spectroscopy senses the super-paramagnetic relaxation. 

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