Abstract
An NMR study of Sm 2Co 17H x ( x = 0, 1.5, 4.6) hydrides is reported. The 147Sm and 149Sm spin echo spectra were measured on powder samples at 4.2 K with no applied magnetic field. The quadrupole septets (nuclear spin I of both Sm isotopes is 7/2) observed in the spectra are attributed to Sm sites with different numbers of hydrogen nearest neighbours located at the 9(e) and 18(g) sites in the crystal structure. Hydrogen neighbours at 9(e) sites cause a decrease of Sm hyperfine field, whereas hydrogen at 18(g) sites causes its increase, which is attributed to the changes of an anisotropic contribution of spin dipolar origin. The 9(e) neighbours cause a decrease of the quadrupole splitting, which corresponds to an increase of the lattice contribution to the electric field gradient. Hydrogen at 18(g) sites causes a slight decrease of the lattice electric field gradient. The results are analysed in terms of electron transfer between hydrogen and samarium sites and the difference between the effect of hydrogen at the 9(e) and 18(g) sites on the magnetocrystalline anisotropy is discussed.
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