Mössbauer Spectroscopy

Contact: Adriana Lančok, Centre of Instrumental Techniques, Laboratory of Low Temperatures

Laboratory of Low Temperatures is a joint department of the Institute of Inorganic Chemistry AS CR, v. v. i., Institute of Physics AV ČR, v. v. i., and the Faculty of Mathematics and Physics and Faculty of Science of the Charles University in Prague.

The scientific program of the laboratory concerns the physical properties of materials containing iron based on the study of hyperfine interactions especially between the nuclei of isotope ⁵⁷Fe and their electron shell. Modern atomic spectroscopic methods found broad applications in physics, chemistry, geology, biology and medicine. These methods are using stable atomic nuclei, especially stable isotope ⁵⁷Fe as local probe in the studied materials. The hyperfine interactions of atomic nuclei are particularly sensitive to the valency state of the ions, local crystal symmetry and defects in the crystal lattice and magnetic ordering.

⁵⁷Fe Mössbauer spectroscopy seems to be an excellent tool to investigate the iron-based nanocrystalline structures, because this local technique is able to elucidate the nature of hyperfine interactions of different iron nuclei and to probe the nature of the surroundings such as type of bonding and valence, number and character of the nearest neighbors, etc. The Mössbauer spectra of the magnetic systems may be acquired either in the transmission mode or by Conversion Electrons Mössbauer Spectroscopy (CEMS) with different information depths for the two methods. As the source for ⁵⁷Fe Mössbauer spectroscopy, ⁵⁷Co diffused in Rh matrix is commonly used. We do not intend to make use of the „source Mössbauer spectroscopy“, where the radioactive atoms of ⁵⁷Co are directly embedded into the studied material as local probes, as this technique belongs from the technological point of view to much more demanding field of radiochemistry.

Typical branches for using Mössbauer spectroscopy is the phase analysis of samples containing compounds and alloys of iron, e.g. in mineralogy, geology, metallurgy, mechanical engineering, chemistry, identification of corrosive products, characterisation of surfaces, study of structural defects by radiation damage etc. For magnetic samples the observation of magnetic structure, texture (for rolled materials) is also possible. Characterization of the surface is enabled by conversion electrons, another possible arrangement of the experiment is the transmission mode (for sample´s thickness about 1 - 100 µm) or detecting the for recoil radiation (for sample´s thickness up to 100 µm).
In our laboratory we may also use external magnetic field up to 6 T and temperatures between 4 - 1000 K for transmission mode, for CEMS only room temperature. We also have the option to measure in-situ in nitrogen and oxygen atmospheres.

Co-ferrites for Medical Applications

Studies of magnetic nanoparticles are significantly motivated by their current and potential applications in biology and medicine like magnetic separation of cells and biomolecules, drug delivery, contrast agents for magnetic resonance paging and colloidal mediators for magnetic hyperthermia of cancer. It is evident that any of the outlined applications has specific requirements. There are two crucial needs for their application in magnetic fluid hyperthermia, in particular high specific power losses leading to high heating efficiency in order to minimize the injected dose and the elimination of local overheating by a self-controlled heating mechanism based on optimally adjusted Curie temperature. The investigated samples have been preliminarily biologically tested on a culture of macrophages subjected to a localized heating by the alternating field of H_max = 10 mT and ν = 500 Hz.

These graphs compare Mössbauer spectra of materials containing nanoparticles (marked NANO) and „bulk“ material (mark BULK) in dependence on  temperature  – the upper pair of spectra; the spectra at the bottom show the decomposition of the 4.2 K, 6 T spectra into contributions corresponding to (A) and [B] spinel sites and various iron neighbourhoods.

Nano-composite Materials – Thin Films

The aim of this work is the preparation of nanocomposite materials containing magnetic nanoparticles, for example FePt, CoFe, Co, Fe. Nanostructured thin films were prepared by a dual radiofrequency magnetron sputtering, physical vapour deposition, pulsed laser deposition or plasma jet deposition. The result was not satisfactory so now we are looking for a suitable combination of these three techniques.

We were studying structural properties (crystal structure and orientation) of layers with nanoparticles for samples which were prepared by all methods. The figure shows the decomposition of the Mössbauer spectrum of thin film.

Photo taken during deposition of Fe thin film fabrication by means of PLD using a Nd:YAG laser operated at 266 nm wavelength.
 

Project Funding

This work was supported by grant GAČR P204/10/0035 (2010-2015).

Papers

• Veverka, M. - Jirák, Z. - Kaman, O. - Knížek, K. - Maryško, M. - Pollert, E, - Závěta, K. - Lančok, A. – Douhá, M. - Vratislav, S. : Distribution of cations in nanosize and bulk Co–Zn ferrites. 2011 Nanotechnology 22 345701.
• Msomi, J. Z. - Abdallah, H. M. I. - Moyo, T. - Lancok, A. : Structural and magnetic properties of MnxCo_1-xFe₂O₄ ferrite nanoparticles. Journal of Magnetism and Magnetic Materials. 323 (2011) 471-474.
• Miglierini, M. - Lancok, A.: Magnetic Behaviour of Ferritin Nanoparticles. Acta Physica Polonica A. 118 (2010) 944-945.
• Lancok, A. – Kohout, J. – Miglierini, M. et al.: Study of Fe-Co Nanocomposite Films. Mössbauer Spectroscopy in Materials Science. 1258 (2010) 82-89.
• Miglierini, M. – Lancok, A. – Kohout, J. : Hyperfine fields in nanocrystalline Fe-Zr-B probed by Fe-57 nuclear magnetic resonance spectroscopy. Applied Physics Letters. 96 (2010) 211902.
• Mustafin, E. - Seidl, T. - Plotnikov, A. - Strasik, I. - Pavlovič, M. - Miglierini, M. - Stancek, S. - Fertman, A. - Lančok, A. : Ion irradiation studies of construction materials for high-power accelerators. Radiation Effects and Defects in Solids. 164 (2009) 460-469.
• Lančok, A. - Fendrych, F. - Miglierini, M. - Kohout, J. – Klementová, M. : Study of hyperfine interactions in Fe–Co nanocomposite films by Mössbauer spectroscopy and NMR. J. Non-Cryst. Solids. 354 (2008) 5255-5257.
• Veverka, M. - Veverka, P. - Kaman, O. - Lančok, A. - Závěta, K. – Pollert, E. – Knížek, K. – Boháček, J. – Beneš, M. – Kašpar, P. – Duguet, E. – Vasseur S. : Magnetic heating by cobalt ferrite nanoparticles. Nanotechnology. 18 (2007) 345704.