Mossbauer single crystal absorber

Fig. 6.12 Mossbauer spectra of a single crystal absorber of Fe(N03)3 9H2O with the absorber plane parallel to the (001) plane. The spectra were obtained at 78 K with a magnetic field of 1.3 T applied in various directions in the absorber plane. B is the angle between the applied field and the [010] direction. (Reprinted with permission from [40] copyright 1974 by Elsevier)...

Fig. 7.23 Mossbauer spectra obtained with a single crystal source and (a) an enriched polycrystalline ZnO absorber (82.5% Zn, 963 mg Zn cm, sintered in oxygen atmosphere at 1,000 K for 24 h), (b) a single crystal absorber of natural ZnO. Both source and absorber were at 4.2 K (from [60])...

Studies with single-crystal absorbers can give the details of f 6). Mossbauer nuclei attached to a surface of a crystal, or embedded in other two-dimensional systems, e.g. Mossbauer nuclei intercalated into graphite, also exhibit large anisotropy in their recoil-free fraction. Several studies of single crystals and two-dimensional systems have been reported. In most cases the isotopes used for the studies were Sn and Fe (Herber Maeda, 1980 Howard Nussbaum, 1980). 

With h 6) - 1/sin 0)5(0 — Oq), one obtains the same result as given by (4.58), which implies that the anisotropy of the/factor cannot be derived from the intensity ratio of the two hyperfine components in the case of a single crystal. It can, however, be evaluated from the absolute/value of each hyperfine component. However, for a poly-crystalline absorber (0(0) = 1), (4.66) leads to an asymmetry in the quadrupole split Mossbauer spectrum. The ratio of l-Jh, as a function of the difference of the mean square amplitudes of the atomic vibration parallel and perpendicular to the y-ray propagation, is given in Fig. 4.19. 

Fig. 7.22 Zn Mossbauer spectrum of ZnO as absorber with a single crystal Ga/ZnO source in applied magnetic field (from [58])...

Fig. 7.27 Mossbauer absorption spectra of a polycrystalline Znp2 absorber recorded between 4.2 and 55.3 K. The source, Ga in a ZnO single crystal, was kept at 4.2 K (from [81])...

Fig. 7.41 Electric quadrupole split Ta (6.2 keV) Mossbauer spectra for sources of diffused into hexagonal transition metals (Re, single crystal Os, polycrystallme Ru, single crystal). The isomer shifts relative to a tantalum metal absorber are indicated by the arrows (from [186, 189])...

Fig. 7.46 Xa Mossbauer spectra of a Ta metal absorber without magnetic field top), with magnetic field applied to the single crystal source only, = 2.8 kG (middle), and...

Determination of the spin directions within the ac plane was accomplished by using a a-Fe source and a single crystal of vivianite at room temperature. The spectra contained many lines because both absorber and source were split, but could be analysed successfully to show that bisects the 104-5° ac angle for the Fe(l) site and that for the Fe(2) site is perpendicular to this. Although the spin axes for both sites at low temperature were thought to be parallel to the direction for Fe(l) an independent investigation by neutron diffraction and Mossbauer methods did not confirm this [55]. The... 

Mossbauer spectroscopy is a nondestructive technique which probes a specific element which may occupy one or more crystallographic sites, may have one or more electronic configurations, and may or may not carry a magnetic moment. The absorbers may be in the form of single crystals, powders, foils, surfaces, or frozen solutions solutions or liquids can not be studied. The influence of temperature, pressure, applied magnetic field, and electromagnetic irradiation is easily studied by Mossbauer spectroscopy. 

It was stated in the preceding section that 2 is a suitable choice of effective absorber thickness. Table 4 presents the needed area density of the lanthanide (in natural isotopic abundance) or the actinide for different measuring temperatures and various Debye temperatures. For intermetallic compounds 0 200 K is a good guess. A typical Mossbauer absorber covers an area of 2-4 cm. For most cases about 0.5 g of material suffices. As said before, powder samples are fine, single crystals are not necessary. 

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