Various Mossbauer Spectroscopy Techniques in Study of Applications Related to Nanocrystalline Iron Oxides

4 VARIOUS MOSSBAUER SPECTROSCOPY TECHNIQUES IN STUDY OF APPLICATIONS RELATED TO NANOCRYSTALLINE IRON OXIDES 

Transmission Mossbauer spectrometer equipped by cryomagnetic system operating with an external magnetic field upto 10T and temperatures down to 1.5 K. 

Schematic representations of various hyperfine interactions affecting the nuciear ieveis of a Mossbauer-active nucieus. (Adapted from Ref. 94 with permission of Cambridge University Press.) 

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]. 

It is well known that a Mossbauer-active nucleus senses its local environment via direct and indirect exchange mechanisms (see Fig. 18.28) [I 1,94]. Direct interactions include (i) interaction between atomic shell and nucleus of a Mossbauer-active atom (interaction of Type I), (ii) interaction between the nucleus of the Mossbauer-active atom and its surrounding lattice (interaction of Type III), and (Mi) interaction between Bext nd nucleus of the Mossbauer-active atom (interaction of Type V). On the other hand, indirect interactions involve (i) interaction between the lattice and atomic shell of the respective nucleus of the Mossbauer-active atom (interaction of Type II) and (ii) interaction between Bgxt and atomic shell of the respective nucleus of the Mossbauer-active atom (interaction of Type IV). Thus, Bgxt can act directly or indirectly on the nucleus of the Mossbauer-active atom and affects its nuclear levels. Beside this, Bgxt can magnetically induce a quadrupole interaction that frequently happens, for example, in the case of Fe having a cubic environment. Interaction of Type IV and Type V can be effectively described by Hamiltonians in the form of [94] 

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