Optical spectroscopy of single- and two-ion transitions in an antiferromagnetic stoichiometric rare-earth crystal

TL;DR

This study investigates the optical properties of Nd3+ ions in antiferromagnetic NdGaO3 under magnetic fields, revealing three magnetic phases and classifying optical transitions, with models explaining single-ion and pair interactions, advancing understanding for quantum transduction.

Contribution

It introduces a comprehensive model for optical transitions in NdGaO3, including single-ion and pair interactions, under various magnetic phases, which was previously unexplored.

Findings

Identified three magnetic phases: antiferromagnetic, intermediate, and paramagnetic.

Classified optical transitions into single-Nd and two-Nd families.

Modeled optical spectra using extended crystal-field Hamiltonian including ion pairs.

Abstract

We characterise optical transitions of neodymium ions (Nd3+) in antiferromagnetic neodymium gallate (NdGaO3) with applied fields up to 3 T. The magnetic phase of this material has not previously been studied with the field along its magnetisation axis. The measured optical spectra indicate three magnetic phases -- antiferromagnetic, intermediate, and paramagnetic -- where the intermediate phase likely forms a different magnetic structure from typical spin-flop phases. The observed absorptions were classified into two distinct families of optical transitions: single-Nd and two-Nd absorptions. We demonstrate that the optical transitions in the antiferromagnetic and paramagnetic phases can be modelled using a standard single-ion crystal-field Hamiltonian that interacts with a mean magnetisation from the rest of the lattice, and we expand that model to encompass pairs of ions, explaining the origins of the two-Nd transitions. This study offers a deeper understanding of the optical transitions in rare-earth antiferromagnetic crystals, which have been recently attracting significant interest for microwave-to-optical quantum transduction, despite being relatively unexplored to date.