Collective excitations in the tetravalent lanthanide honeycomb antiferromagnet, Na2PrO3

TL;DR

This study investigates the magnetic excitations in Na2PrO3, revealing dominant Heisenberg interactions and crystal-field effects that influence its antiferromagnetic properties and complicate static magnetic detection.

Contribution

It provides the first detailed analysis of magnetic fluctuations and exchange interactions in Na2PrO3, highlighting the role of crystal-field excitations and anisotropic exchange in this lanthanide honeycomb magnet.

Findings

Magnetic fluctuations observed below 2 meV energy.

Crystal-field excitations around 230 meV.

Dominant Heisenberg exchange interaction J ≈ 1.1 meV.

Abstract

Thermomagnetic and inelastic neutron scattering measurements on Na2PrO3 are reported. This material is an antiferromagnetic honeycomb magnet based on the tetravalent lanthanide Pr4+ and has been proposed to host dominant antiferromagnetic Kitaev interactions. These measurements reveal magnetic fluctuations in Na2PrO3 below an energy of 2 meV as well as crystal-field excitations around 230 meV. The latter energy is comparable to the scale of the spin-orbit interaction and explains both the very small effective moment of around 1.0 {\mu}B per Pr4+ and the difficulty to uncover any static magnetic scattering below the ordering transition at TN = 4.6 K. By comparing the low-energy magnetic excitations in Na2PrO3 to that of the isostructural spin-only compound, Na2TbO3, a microscopic model of exchange interactions is developed that implicates dominant and surprisingly large Heisenberg exchange interactions J approximately equal to 1.1(1) meV. Although antiferromagnetic Kitaev interactions with K less than or equal to 0.2J cannot be excluded, the inelastic neutron scattering data of Na2PrO3 is best explained with a delta = 1.24(2) easy-axis XXZ exchange anisotropy.