Zero field NMR study on a spin glass: Iron-doped 2H-niobium diselenide

We have used spin echoes to study the 93Nb NQR in 2H-NbSe2Fex. We measured (intensity)x(temperature), and T1P (spin-lattice relaxation parameter) and T2 (spin-spin relaxation time) as a function of temperature. Our data reveal dramatic difference between non-spin glass samples (x=O, 0.25%, 1% and 5%) and spin glass samples (x=8%, 10% and 12%). Defining the spin glass transition temperature Tg by the cusp of the susceptibility versus temperature curve, we find a well defined minima at T:Tg tn (intensity)x(temperature), T1P and T2 as a function of temperature. Deduction of a correlation time of Fe spins from T1P and T2 is complicated by the intensity changes which imply that 0ne observes different groups of nuclei at different temperatures. We propose a two-correlation-time model, which utilizes the anisotropy of the exchange interaction, to overcome this difficulty. All of our NQR results and the model calculation of the correlation times of Fe spins are best described by the phase transit ion picture of spin glasses.U of I OnlyThesi