Titanium nuclear magnetic resonance in metallic superconducting lithium titanate and its lithium-substituted derivatives Li_1+xTi_2-xO₄ (0<x<0.10)

One of the first reported oxide superconductors lithium titanate Li_1+xTi_2-xO₄ (T_c∼12 K for 0<x<0.10) is studied here by nuclear magnetic resonance of the titanium nucleus (⁴⁹Ti and ⁴⁷Ti) in the temperature range 160–330 K. The study encompasses the temperature variation of the Knight-shift components and the quadrupole interaction for LiTi₂O₄ (the x=0 end member), the variation of the spectrum at room temperature as a function of x in the range 0<x<0.10, and some preliminary measurements of the nuclear spin-lattice relaxation time. The samples have been well characterized by a combination of x-ray and neutron diffraction, and magnetic-susceptibility (superconducting quantum interference device ac inductance) measurements. A feature of the present samples is the very low density of localized moments in the metallic regime, as compared to previous studies of the same system. The results show strong broadening of the Ti spectrum induced by lithium substitution and fast relaxation. The isotropic and axial Knight-shift components and the quadrupole interaction in LiTi₂O₄ exhibit a strong temperature dependence. The isotropic Knight-shift component is linked to a temperature variation of the electron spin susceptibility χ, leading to an estimate of the average orbital susceptibility in the x=0 compound of 30×10^-6 emu/mole, a value corroborated by theoretical calculations. The axial component of the shift indicates that both the orbital and the spin susceptibilities in the x=0 compound are highly anisotropic. The values of isotropic shift and χ indicate that the electronic system at x=0 is a narrow d-band metal with significant electron-electron interaction.