7Li and 51V NMR study of the heavy-fermion compound LiV2O4

Li-7 and V-51 NMR Knight shift, linewidth, spin-lattice, and spin-spin relaxation rate data are reported as a function of temperature T (1.5-800 K and 74-575 K for Li and V nuclei, respectively) in the heavy fermion compound LiV2O4. The Li-7 Knight shift K exhibits a broad maximum at about 25 K and is nearly constant below 4.2 K, as is the linewidth. The V-51 Knight shift is negative at 575 K and it decreases strongly as the temperature is lowered. Above similar to 80 K, both Li-7 and V-51 Knight shifts are proportional to the susceptibility and from the slope the hyperfine coupling constant can be obtained for both nuclei. The Li-7 spin-lattice relaxation rate increases as the temperature is lowered below room temperature reaching a maximum at about 50 K. Below 5 K the relaxation rate decreases linearly with T as for normal metals but with a very high value of the Korringa product (T1T)(-1). Even so, the Li-7 Korringa ratio (KT1T)-T-2/S-Li below similar to 10 K is on the order of unity as in conventional metals, thus indicating heavy Fermi liquid behavior. From an analysis of the Li-7 and V-51 relaxation rate data we infer an approximate square root temperature dependence of the V local moment spin-relaxation rate at high temperatures (T greater than or similar to 50 K). A simplified analysis of the data yields a value of 17 meV for the magnitude of the exchange coupling constant between the local moments and the conduction electrons and 2.3 meV for that between neighboring local moments. Quantitative discrepancies in the Li-7 and V-51 relaxation rates at low T from what is expected for a uniform heavy Fermi liquid indicate that effects such as Kondo effect screening of the V local moment and/or dynamical vanadium t(2g) orbital occupation correlation/ fluctuation effects may be present in our system. [S0163-1829(98)00715-2].