Magnetic field dependence of antiferromagnetic resonance in NiO

TL;DR

This study investigates how magnetic fields and temperature affect antiferromagnetic resonances in NiO using terahertz spectroscopy, revealing complex mode behaviors that challenge simple models.

Contribution

It demonstrates the limitations of two-sublattice models and highlights the importance of magnetic dipolar interactions and anisotropy in NiO's spin dynamics.

Findings

Two distinct antiferromagnetic resonance modes identified.

Magnetic field dependencies differ between the modes.

Two-sublattice model insufficient for describing NiO dynamics.

Abstract

We report on measurements of magnetic field and temperature dependence of antiferromagnetic resonances in the prototypical antiferromagnet NiO. The frequencies of the magnetic resonances in the vicinity of 1 THz have been determined in the time-domain via time-resolved Faraday measurements after selective excitation by narrow-band superradiant terahertz (THz) pulses at temperatures down to 3K and in magnetic fields up to 10 T. The measurements reveal two antiferromagnetic resonance modes, which can be distinguished by their characteristic magnetic field dependencies. The nature of the two modes is discussed by comparison to an eight-sublattice antiferromagnetic model, which includes superexchange between the next-nearest-neighbor Ni spins, magnetic dipolar interactions, cubic magneto-crystalline anisotropy, and Zeeman interaction with the external magnetic field. Our study indicates that a two-sublattice model is insufficient for the description of spin dynamics in NiO, while the magnetic-dipolar interactions and magneto-crystalline anisotropy play important roles.