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Ultrafast demagnetization in bulk versus thin films: an ab initio study.
Summary
Surface effects dramatically amplify laser-induced demagnetization in nickel (Ni) thin films due to enhanced spin currents. Bulk nickel demagnetization is primarily driven by spin-orbit coupling-induced spin-flips.
Area of Science:
- Condensed matter physics
- Quantum dynamics
- Materials science
Background:
- Understanding laser-matter interactions is crucial for manipulating magnetic properties.
- Nickel (Ni) is a key material in spintronics and magnetic storage.
Purpose of the Study:
- To investigate the quantum dynamics of electronic charge and spins in Ni under intense laser pulses.
- To compare demagnetization processes in Ni thin films versus bulk Ni.
- To elucidate the role of surfaces and spin-orbit coupling in laser-induced demagnetization.
Main Methods:
- Ab initio simulations of quantum dynamics.
- Electron-dynamics calculations for Ni thin films and bulk.
- Comparison with experimental data.
Main Results:
- Surface formation dramatically amplifies laser-induced demagnetization in Ni thin films.
- Enhanced spin currents on thin film surfaces contribute to amplified demagnetization.
- Bulk Ni demagnetization is dominated by spin-orbit coupling-induced spin-flips.
- Thin film demagnetization involves both spin currents and spin-flips.
- Electronic processes dominate demagnetization below ~120 fs, followed by dissipative effects.
Conclusions:
- Surface effects play a critical role in laser-induced demagnetization of Ni.
- Quantum electronic dynamics are the primary drivers of ultrafast demagnetization.
- Spin currents and spin-orbit coupling are key mechanisms in Ni demagnetization.
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