A theoretical study of the nuclear spin-lattice relaxations of HCP transition metals

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Abstract
The spin-lattice relaxation rates of HCP transition metals (Sc, Ti, Y, Zr and Tc) are calculated based on the ab initio semi-relativistic ASA-SCF-LMTO linear tetrahedron scheme. A thorough investigation of the off-diagonal contributions is presented. The off-diagonal contribution amounts to some 20% of the total relaxation rate and plays an important role in the anisotropy of the relaxation rate. The theoretical relaxation rates reproduce the experiments very well for Ti, Y and Tc, but some discrepancies do exist for Sc. It is suggested that the relativistic and exchange enhancements of the core polarisation would reduce the discrepancy in Sc significantly but make the agreement slightly worse for Y. As for Zr, the theoretical relaxation rate is about twice the experimental one. The reason for the discrepancy is not clear at present. It will be shown that the p contribution is very important for all the HCP transition elements studied here and that the contribution of the quadrupolar interaction is not negligibly small for 47Ti.

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