High-temperature spin-wave propagation in BiFeO3: relation to the Polomska transition

TL;DR

This study demonstrates that a specific spin wave in BiFeO3 thin films remains underdamped and propagating up to 455 K, revealing temperature-dependent behavior linked to the Polomska transition, with implications for room-temperature device applications.

Contribution

It provides the first measurement of the high-temperature spin wave in BiFeO3 and links its damping behavior to the Polomska transition, advancing understanding of spin dynamics in this material.

Findings

Spin wave persists as underdamped up to 455 K

Spin wave frequency follows a Brillouin function indicating high-spin Fe3+ ions

Propagation of spin wave ceases above 455 K, near the Polomska transition

Abstract

In bismuth ferrite thin films the cycloidal spiral spin structure is suppressed, and as a result the spin-wave magnon branches of long wavelength are reduced from a dozen to one, at \omega = 19.2 cm-1 (T=4K). This spin wave has not been measured previously above room temperature, but in the present work we show via Raman spectroscopy that it is an underdamped propagating wave until 455 K. This has important room-temperature device implications. The data show that \omega(T) follows an S=5/2 Brillouin function and hence its Fe+3 ions are in the high-spin 5/2 state and not the low-spin S=1/2 state. The spin wave cannot be measured as a propagating wave above 455 K. We also suggest that since this temperature is coincident with the mysterious "Polomska transition" (M. Polomska et al., Phys. Stat. Sol. A 23, 567, (1974)) at 458+/-5 K, that this may be due to overdamping.