Grant-funded Project Nr. 170/2000/B-FYZ/MFF
Final Report

Project title:Study of cation distribution, valence states and hyperfine interactions in ferrites with paramagnetic substitutions
Research leader:Doc.RNDr. Helena Štěpánková, CSc.
Co-researcher: Mgr. Jaroslav Kohout, Dr.; Ing. Oleksiy Snezhko; Ing. Olena Gamaliy
Period of project:2000-2002
Overall grant:478 000 CZK

Project Results

The project is devoted to the study of magnetic iron oxides using hyperfine methods, namely nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR). The experiments were performed using broad-band pulse coherent NMR spectrometer at MFF UK. The measurements were carried out on nominally pure and substituted iron garnets and magnetites. Resonance of isotopes 57Fe, 155Gd and 157Gd  was detected. The satellite structure in 57Fe NMR spectra induced by substitutions, the temperature dependences of spectra and the changes in relaxation rates were measured. The hyperfine field modification was investigated for various paramagnetic and nonmagnetic aimed substitutions with either the same or different valence as the replaced cation. The results concern the correspondence of hyperfine interations to the crystal and electronic structure.
Particularly the following systems and dependences were monitored:
1.  Replacing of Y with Gd in iron garnets in a full concentration range – satellite structure of 57Fe NMR, testing of additivity principles, temperature dependences.
2. Gadolinium iron garnet – analysis of hyperfine parameters on gadolinium sites at low temperatures.
3. Replacing of Y with Bi in iron garnets in a full concentration range – satellite structure of 57Fe NMR, additivity principle, correspondence of NMR spectrum to the garnet structure for the unique film of bismuth iron garnet..
4. Comparative study of iron relaxation rates dependence on the substitution type (Al, In, Ca, La) and its concentration in well defined series of yttrium iron garnet (YIG) films prepared by LPE from barium oxide flux.
5. Comparative study of the influence of Al substitution on iron hyperfine parameters in YIG and magnetite.
6. Replacing of iron with Co and Rh  in YIG – satellite structure of 57Fe NMR spectra.
The results were presented at international conferences (1 invited, 1 oral contribution, 6 posters) and in 8 papers:
[1] Novák P, Štěpánková H, Englich J, et al., Temperature dependence of NMR in magnetite, Proc. Int. Conf. Ferrites, Kyoto 2000, p.131
[2] Kohout J, Englich J, Štěpánková H, et al., Anisotropy of 57Fe hyperfine field in La substituted YIG, Proc. Int. Conf. Ferrites, Kyoto 2000, p.208
[3] Štěpánková H, Kohout J, Englich J, et al., Hyperfine interactions in Y3-xGdxFe5O12, Proc. Int. Conf. Ferrites, Kyoto 2000, p. 325
[4] Gamaliy E, Štěpánková H, Englich J, Kohout J, Snezhko A, Novák P, Brabers VAM, NMR of Fe57 above the Verwey transition in Al-substituted magnetite, J. Magn. Magn. Mater. 242 (2002) 732
[5] Kohout J, Englich J, Štěpánková H, Kuriplach J, Nižňanský D., Hyperfine interaction of Gd155 in gadolinium iron garnet, J. Magn. Magn. Mater. 242 (2002) 763
[6] Gamaliy E, Štěpánková H, Kohout J, Snezhko A, Kučera M, Nitsch K, Effect of aluminium substitution in YIG on iron hyperfine field anisotropy, J. Magn. Magn. Mater. 242 (2002) 766
[7] Gamaliy E, Snezhko A, Štěpánková H, Kučera M, Nitsch K, Nuclear magnetic relaxation in YIG films with nonmagnetic trivalent substitutions, J. Magn. Magn. Mater. 242 (2002) 769
[8] Štěpánková H, Okuda T., Gamaliy E, Snezhko A, Adachi N, Kaneuji T, Nuclear magnetic resonance of 57Fe in bismuth-yttrium iron garnets,  Phys. Stat. Sol.a 196 (2003) 121