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

TL;DR

This study investigates how pressure influences spin fluctuations in YMn₂, revealing a transition from SCR theory behavior to deviations associated with short-range AF fluctuations and Fermi liquid characteristics.

Contribution

It provides new insights into pressure-induced changes in spin fluctuation behavior and their relation to Fermi liquid properties in YMn₂.

Findings

Spin fluctuation feature changes below a critical temperature T_sf.

T_sf coincides with the temperature where T² resistivity law applies.

Development of AF spin fluctuations remains short-range with singlet formation.

Abstract

We report the NQR study on the pressure-induced paramagnetic state in the antiferromagnetic (AF) intermetallic compound YMn$_2$ with the N\'eel 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 $1/T_1T$ 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 $Y_{1-x}Sc_xMn_2$.