Pressure Effect on the Spin Fluctuations in YMn₂

Mn NQR Study

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We report the NQR study on the pressure-induced paramagnetic state in the antiferromagnetic (AF) intermetallic compound YMn₂ with the Néel temperature T_N =100 K at ambient pressure. From the T variation of the nuclear spin-lattice relaxation rate, ⁵⁵ (1/T₁) of ⁵⁵Mn above the critical pressure of 4 kbar, the spin fluctuation feature is found to change below a temperature T_sf. At higher temperature than T_sf, 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_sf a deviation is significant and 1/T₁T exhibits a weak T variation. It is pointed out that T_sf coincides with the temperature below which a T² law in electrical resistivlty is valid as expected for a Fermi 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.