Hole Doping Effects on Spin-gapped Na2Cu2TeO6 via Topochemical Na Deficiency

TL;DR

This study investigates how hole doping via Na deficiency and nonmagnetic Zn substitution affect the magnetic properties of the spin-gapped compound Na2Cu2TeO6, revealing distinct magnetic behaviors and spin dynamics.

Contribution

It provides new insights into the effects of topochemical Na deficiency and Zn impurities on the magnetic and spin dynamics of Na2Cu2TeO6.

Findings

Na deficiency induces spin glass behavior.

Zn impurities enhance low-temperature relaxation rates.

Hole doping suppresses certain spin relaxation processes.

Abstract

We report the magnetic susceptibility and NMR studies of a spin-gapped layered compound Na2Cu2TeO6 (the spin gap $\Delta\sim$ 250 K), the hole doping effect on the Cu2TeO6 plane via a topochemical Na deficiency by soft chemical treatment, and the static spin vacancy effect by nonmagnetic impurity Zn substitution for Cu. A finite Knight shift at the $^{125}$Te site was observed for pure Na2Cu2TeO6. The negative hyperfine coupling constant $^{125}A_{tr}$ is an evidence for the existence of a superexchange pathway of the Cu-O-Te-O-Cu bond. It turned out that both the Na deficiency and Zn impurities induce a Curie-type magnetism in the uniform spin susceptibility in an external magnetic field of 1 T, but only the Zn impurities enhance the low-temperature $^{23}$Na nuclear spin-lattice relaxation rate whereas the Na deficiency suppresses it. A spin glass behavior was observed for the Na-deficient samples but not for the Zn-substituted samples. The dynamics of the unpaired moments of the doped holes are different from that of the spin vacancy in the spin-gapped Cu2TeO6 planes.