Thermal evolution of the full three-dimensional magnetic excitations in the multiferroic BiFeO3

TL;DR

This study investigates the temperature-dependent behavior of three-dimensional magnetic excitations in multiferroic BiFeO3 using neutron scattering, revealing well-defined magnons at low temperatures and significant damping near the magnetic transition.

Contribution

It provides the first comprehensive measurement of spin-wave dispersion in BiFeO3 across a wide temperature range, highlighting the effects of electromagnetic coupling and hybridization on magnetic excitations.

Findings

Magnetic excitations behave like conventional magnons across all temperatures.

Spin-waves are well-defined at low temperatures and soften with increasing temperature.

Hybridization of Fe 3d and O 2p states significantly influences spectral weight distribution.

Abstract

The idea of embedding and transmitting information within the fluctuations of the magnetic moments of spins (spin waves) has been recently proposed and experimentally tested. The coherence of spin waves, which describes how well defined these excitations are, is of course vital to this process, and themost significant factor that affects the spin-wave coherence is temperature. Here we present neutron inelastic scattering measurements of the full threedimensional spin-wave dispersion in BiFeO3, which is one of the most promising functional multiferroic material, for temperatures from 5K to 700K. Despite the presence of strong electromagnetic coupling, the magnetic excitations behave like conventional magnons over all parts of the Brillouin zone. At low temperature the spin-waves are well-defined coherent modes, described by a classical model for a G-type antiferromagnet. A spin-wave velocity softening is already present at room temperature, and more pronounced damping occurs as the magnetic ordering temperature TN \sim 640K is approached. In addition, a strong hybridization of the Fe 3d and O 2p states is found to modify the distribution of the spin-wave spectral weight significantly, which implies that the spins are not restricted to the Fe atomic sites as previously believed.