Persistence of Ising-like easy-axis spin correlations in the paramagnetic state of the spin-1 chain compound NiTe$_2$O$_5$

TL;DR

This study uses $^{125}$Te NMR to reveal persistent Ising-like uniaxial spin correlations in the paramagnetic state of NiTe$_2$O$_5$, a quasi-one-dimensional spin-1 chain compound, indicating strong anisotropic magnetic fluctuations.

Contribution

It provides the first detailed NMR analysis showing that Ising-like spin correlations persist at high temperatures in NiTe$_2$O$_5$, highlighting the role of transverse spin fluctuations.

Findings

Line splitting indicates sublattice susceptibilities along chains.

Dominant transverse spin fluctuations observed in relaxation and Knight shift.

Uniaxial spin correlations persist up to high temperatures.

Abstract

A $^{125}$Te nuclear magnetic resonance (NMR) study was carried out in the paramagnetic state of the recently discovered quasi-one-dimensional spin-1 chain compound NiTe$_2$O$_5$. We observed that the $^{125}$Te NMR spectrum splits into two in a magnetic field applied along the $c$ axis. Based on the strong temperature variation of the relative intensity ratio of the split lines, we infer that the line splitting arises from the two sublattice susceptibilities induced in opposite directions along the chains. In great support of this interpretation, a quantitative analysis of the spin-lattice relaxation rate $T_1^{-1}$ and the Knight shift data unravels dominant transverse spin fluctuations. We conclude that Ising-like uniaxial spin correlations persist up to surprisingly high temperatures compared to the exchange energy scales. Spin-charge coupling mechanism via a self-doping effect may be important.