Other than the crystal orientation with regard to gamma rays, which factors influence the intensity of the 2nd and 5th? How effectively does the sampling or the morphology of the sample affects the width?
The relative orientation of the magnetization with the gamma rays give the height of peak n°2!
Thank u all for sharing the knowledge. The Mossbauer spectrum in the case of cold rolled sample the orientation effect at the dislocation site is understandable but in nano particles we often have A23 > 2. Whether is there any self orientation effect in nano powder?
You can also look at that paper. Strain-induced magnetic anisotropy in single-crystal
RFe2(110) thin films (R = Dy, Er, Tb, Dy0.7Tb0.3, Sm, Y)PHYSICAL REVIEW B Volume: 6214 Pages: 9517-9531
We add both in-plane and out of plane epitaxial thin films!
Electric field gradients give shifts of Moessbauer lines. In nanoparticles with a very high surface/volume ratio there is going to be a wide distributions of EFGs.
@Kai Fauth
General speaking, when the size scale of a compound is on the order of nanometers, electron motion is restricted in dimensions, which will directly affect the density of state and, of course, some properties.
I am only familiar with nano-magnetic materials. I once measured the Mossbauer spectrum of nano-sized Fe3O4 and a broad sextet was observed. When the size is small enough, the energy of thermal motion is comparable to the Magnetic Energy. In this case, magnetic relaxation time will be affect, which usually have a linear relationship to the line width. Detailed relationship can be found in paper J. Physique 47 (1986) 1395-1404
Xiaoming, thank you for replying. Compare your previous reply and Carsten's: "size effect" is very unspecific (no physics learned), "surface to volume ratio induced distribution of EFG's" tells me exactly a possible physical origin of line broadening. We should strive for answers that hit the spot.
@ Xiaoming and Kai Fauth, width of the Mossbauer spectrum depends upon the Heisenberg uncertainty, does the uncertainity of the surface atoms is different from that of the core or is the broadening is due to the superposition of different spectrum with nearly different Bhf.
Herojit, are you sure Heisenberg is in place here? The spectral width due to Heisenberg's uncertainty relation is related to the lifetime of the nuclear transition. Here, we are talking about distributions (inhomogeneous) of pararameters which determine the spectral positions. This is statistics which has little if anything to do with Heisenberg's uncertainty relation.
There is a dynamic effect that depends on magnetic relaxation, see e.g. the paper cited below. Basically, if the magnetic relaxation time is comparable to the decay time of the excited nucleus, then you get effects that broaden and distort the Moessbauer spectrum. Xiaoming is pointing out that in nanoparticles the magnetic relaxation may be driven by phonons.
A static EFG effect as I proposed above and a dynamic, phonon-driven effect could be distinguished by looking at the spectra as function of temperature. In particular, the EFG effect should still be there in the high-temperature paramagnetic phase.
Phys. Rev. Lett. 14, 96–98 (1965)
Magnetic Relaxation and Asymmetric Quadrupole Doublets in the Mössbauer Effect
M. Blume
@ Kai Fauth, from the literature the widht of the spectrum was depending on the lifetime . If the nuclear lifetime of the Fe has to be similar for every compound then why the width of different compounds vary. If not so, on what factor does the lifetime varies resulting in the variation of the width. These was the question came in my mind and dint get the appropriate answer. I would be thankful if anybody clears my doubt. (this width variation was derived from the experiment done on the Fe and SS foil of similar thickness).
Dear Herojit Loushambam, I think there are now ample elements in the thread that (at least partially) answer this aspect of the question. There may be static and dynamic processes which (essentially) do not alter the nuclear decay. The broadening is then extrinsic, "inhomogeneous".
There also are dynamic processes that DO alter the nuclear decay (and of which I was unaware), in this case there is also a modified lifetime broadening.
For completeness I would just like to add that the Moessbauer effect can also be observed in the time domain. This group of techniques is called nuclear resonance, in particular nuclear forward scattering.
In short, all Moessbauer nuclei are coherently excited by a very short pulse of synchrotron radiation, and you then look for the decay photon as function of delay. The splitting of the energy levels manifests itself as oscillations of the observed intensity, superposed with the exponential decay.
http://www.esrf.eu/UsersAndScience/Experiments/DynExtrCond/ID18/
U. van Bürck, D. P. Siddons, J. B. Hastings, U. Bergmann, and R. Hollatz
Nuclear forward scattering of synchrotron radiation
Phys. Rev. B 46, 6207–6211 (1992)
http://prb.aps.org/abstract/PRB/v46/i10/p6207_1
In NFS you can also observe a speedup effect where the intensity decays faster than the natural life time.
Homogeneous and inhomogeneous effects alter the line shape, but errors due to the saturation of the spectra are also to be taken into account
The second one
The Mossbauer spectrum is usually an absorption spectrum and the maximum absorption cannot be grater than a given value.
If you consider, for example, a standard iron foil spectrum, the ratio between the relative thicknesses for the #1 and #3 lines ( ta13 ) is 3 but we have A13 < 3 for the corresponding area ratio. For the same reason A23 < 2 also for an ideal random oriented sample.
Consequently, if the fitting procedure does not correctly describe the saturation of the spectra, one can get erroneous evaluation of the physical parameters.
Therefore, in my opinion, it is better to refer to the ta23 ratio ( instead of A23) and the Mossbauer experiment must be associated with a series of ancillary measurements.
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