Pressure Effect on the Spin Fluctuations in YMn${}_2$ --Mn NQR Study--

Abstract

We report the NQR study on the pressure-induced paramagnetic state in the antiferromagnetic (AF) intermetallic compound YMn${}_2$ with the Néel temperature T_N=100 K at ambient pressure. From the $T$ variation of the nuclear spin-lattice relaxation rate, ${}^{55}(1/T_1)$ of ${}^{55}$Mn 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 $1/T_{1}T$ exhibits a weak $T$ variation. It is pointed out that $T_{sf}$ coincides with the temperature below which a $T^2$ law in electrical resistivity 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 $Y_{1-x}S{c}_{x}M{n}_2$.

8 pages, 3 figures