Out-of-plane magnetic phase diagram of Kitaev quantum spin liquid candidate Na2Co2TeO6

TL;DR

This study maps the magnetic phase diagram of Na2Co2TeO6, revealing complex magnetic transitions and plateau-like features under high magnetic fields, with implications for understanding Kitaev interactions in this material.

Contribution

The paper provides the first detailed out-of-plane magnetic phase diagram of Na2Co2TeO6, identifying magnetic transitions and constraining exchange interactions relevant to Kitaev physics.

Findings

Observation of a thermal transition at 27 K from paramagnetic to ferrimagnetic state.

Identification of a spin flop-like transition before saturation under magnetic fields.

Detection of a peak-dip-peak structure in susceptibility indicating magnetic plateau behavior.

Abstract

We have investigated the magnetic properties and mapped out the phase diagram of the honeycomb magnet Na2Co2TeO6 with Co 3d7 in out-of-plane magnetic fields. This material has previously been proposed to show nearest-neighbor Kitaev interactions between Co spins and maybe even Kitaev quantum spin liquid behavior in high fields. At low magnetic fields, we observe a thermal phase transition at TN = 27 K, transitioning from a paramagnetic state to a canonical ferrimagnetic state. Under the application of magnetic fields, a spin flop-like phase transition occurred before saturation of J = 1/2 between 10 K and TN. Below 10 K, a peak-dip-peak structure emerges between 10 and 17 T in the magnetic susceptibility (dM/dH) before the magnetic saturation, reminiscent of magnetic plateau behavior. The measurement of the magnetocaloric effect also shows dip-peak-dip behavior in this field range. Our data can be explained by an XXZ model with a single ion anisotropy and possibly small Kitaev and {\Gamma} exchange interactions. We also unambiguously determined the magnetization saturation field that helps constrain the energy scale of the exchange interactions