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Polarized phonons carry angular momentum in ultrafast demagnetization
S R Tauchert1,2, M Volkov1,2, D Ehberger2
1Universität Konstanz, Fachbereich Physik, Konstanz, Germany.
Nature
|February 3, 2022
Summary
Ultrafast laser pulses rapidly demagnetize nickel films by exciting unique, long-lasting, anisotropic phonons. These circularly polarized phonons absorb the spin system's angular momentum, explaining rapid magnetic order loss.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Ultrafast Phenomena
Background:
- Magnetic phenomena are crucial for technology, but rapid control of magnetic order is challenging.
- Ultrashort laser pulses can demagnetize materials like nickel on femtosecond timescales, opening avenues for ultrafast spintronics.
Purpose of the Study:
- To investigate the mechanism behind ultrafast demagnetization in nickel films.
- To identify the fate of angular momentum during rapid magnetic order loss.
Main Methods:
- Utilized ultrafast electron diffraction to probe atomic dynamics.
- Analyzed the temporal evolution of material properties after laser excitation.
Main Results:
- Observed an instantaneous, long-lasting population of anisotropic high-frequency phonons (150-750 fs) in nickel.
- Determined that phonon anisotropy plane is perpendicular to initial magnetization with 2 pm oscillation amplitude.
- Proposed circularly polarized phonons absorb angular momentum from the spin system.
Conclusions:
- Demagnetization time is linked to atomic acceleration via phonon excitation.
- Provides an atomistic explanation for the Einstein-de Haas effect.
- Highlights the significance of polarized phonons in non-equilibrium dynamics and phase transitions.
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