Temperature dependent magnon-phonon coupling in bcc Fe from theory and experiment

Area of Science:

• Condensed matter physics
• Materials science
• Computational physics

Background:

• Phonon properties are crucial for understanding material behavior.
• Accurately modeling temperature-dependent phonon shifts, especially in magnetic materials, remains challenging.
• Existing models often struggle to bridge the gap between ferromagnetic and paramagnetic states.

Purpose of the Study:

• To develop a novel ab initio based framework for quantitatively assessing phonon contributions from magnon-phonon interactions and lattice expansion.
• To provide a unified approach that accurately describes phonon behavior across magnetic transitions.
• To investigate the influence of magnetic short-range order on phonon frequencies.

Main Methods:

• Development of a first-principles computational framework.
• Quantitative assessment of phonon frequency shifts.
• Inclusion of both magnon-phonon coupling and lattice expansion effects.
• Application to body-centered cubic (bcc) iron (Fe).

Main Results:

• The developed theoretical framework shows excellent agreement with experimental phonon frequency measurements for bcc Fe.
• Magnon-phonon interactions were found to significantly influence phonon frequencies, often exceeding the effects of lattice expansion.
• The impact of magnetic short-range order on phonon properties was demonstrated to be substantial, persisting well above the Curie temperature.
• The framework successfully bridges the simulation gap between the ferromagnetic and paramagnetic limits.

Conclusions:

• The new framework provides a robust method for studying temperature-dependent phonon properties in magnetic materials.
• Magnon-phonon interactions play a dominant role in phonon frequency renormalization, particularly near magnetic transition temperatures.
• The study highlights the importance of considering magnetic correlations even in the paramagnetic phase.