23Na and 75As NMR Study of Antiferromagnetism and Spin Fluctuations on NaFeAs Single Crystals

TL;DR

This study uses $^{23}$Na and $^{75}$As NMR to investigate antiferromagnetism and spin fluctuations in NaFeAs single crystals, revealing how structural and magnetic transitions are affected by temperature and pressure.

Contribution

It provides new insights into the magnetic and structural phase transitions of NaFeAs through detailed NMR measurements under varying conditions.

Findings

Structural transition at 55 K and SDW at 40.5 K identified by NMR line splits.

Spin fluctuations are strongly enhanced below the structural transition.

Applying 2.5 GPa pressure raises $T_{SDW}$ by ~7 K and increases magnetic moments by 30%.

Abstract

We report the $^{23}$Na and $^{75}$As NMR studies on NaFeAs single crystals. The structure transition temperature $T_S$ (55 K) and the spin density wave (SDW) transition temperature $T_{SDW}$ (40.5 K) are determined by the NMR line splits. The spin-lattice relaxation rates indicate that the spin fluctuations are strongly enhanced just below $T_S$ and drive a second order SDW transition. A fluctuating feature of the SDW ordering is also seen below the $T_{SDW}$. We further performed high-pressure NMR studies on NaFeAs, and found that the $T_{SDW}$ increases by $\sim$7 K and the magnetic moment increases by 30% under 2.5 GPa pressure.