Knight shift, spin-lattice relaxation and electric field gradient in technetium metal

Abstract

Spin-lattice relaxation time (T 1), isotropic Knight shift (K iso) and quadrupole coupling constant (C Q) have been measured in technetium metal by pulsed 99 Tc NMR in a magnetic field of 7.04 T in the temperature range 120-400 K. It was found that (T 1 × T) −1 = 3.21 ± 0.35 (s K) −1 , K iso (T) = 7305 − 1.52T ppm; the quadrupole coupling constant C Q = 5.74 ± 0.05 MHz is temperature independent. Experimental data on T 1 and K iso are analysed in terms of the contact, d-polarization and orbital hyperfine interactions. It is shown that the main contribution to the relaxation rate comes from the contact interaction and the Knight shift is governed by the orbital interaction. The electric field gradient at 99 Tc nucleus site is considered to be a sum of the electron q el and lattice q lat contributions with different signs. The calculated lattice contribution is positive and constitutes about 30% of the electronic contribution. The obtained values of q el and q lat are compared with data for other metals with hexagonal closepacked lattices.

Structural and magnetic properties ofTcn@C60endohedral metalofullerenes: First-principles predictions

“…4 we plot the total electronic magnetic moment of free Tc n clusters and of Tc n @C 60 EMFs, obtained using the PW91 and PBE functionals, as a function of the cluster size n. A nonzero magnetic moment is rather unexpected in these systems in view of the fact that Tc is nonmagnetic as bulk metal, 50 with weak paramagnetism only occurring when in contact with a system containing unpaired electrons in the highest occupied level. 51 Unlike in the free Tc n clusters, with the exception of n = 1 and n = 3, the calculated magnetic mo- ment of Tc n @C 60 EMFs is zero. The reason for the suppression of the magnetic moment in large encapsulated Tc n clusters lies in the formation of covalent bonds between Tc atoms and the C shell atoms.…”