Pressure Effect on the Spin Fluctuations in YMn₂ Mn NQR Study

We report the NQR study on the pressure-induced paramagnetic state in the antiferroinagrietic (AF) intermetal-lic compound YMn₂ with the Néel temperature T_N=100 K at ambient pressure. Froin the T variation of the nuclear spin-lattice relaxation rate, ⁵⁶(lJT₁) of ⁵⁵Mn above the critical pressure of 4 kbar, the spin fluctuation feature is found to change below a temperature T_af. At higher temperature than T_af, the nuclear relaxation behavior is well described in terms of the self-consistent renomalized (SCR) spin fluctuation theory for nearly AF metals, whereas below T_af a deviation is significant and 1JT₁T exhibits a weak T variation. It is pointed out that T_af coincides with the temperature below which a T² law in electrical resistivity is valid as expected for a Feimi liquid ground state. We proposed that these features are understood from the standpoint that the development of AF spin fluctuation remains in short-range associated with the singlet formation among Mn spins in each tetrahedron as suggested by the inelastic neutron experiments on Y_1−xSc_xMn₂.