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Spin currents during ultrafast demagnetization of ferromagnetic bilayers
A Eschenlohr1, L Persichetti2, T Kachel3
1Fakultät für Physik, Universität Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany.
Summary
Ultrafast spin currents in layered metals influence magnetization dynamics. Optimizing layer thickness and interface properties is crucial for efficient use of these spin currents in spintronic devices.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Ultrafast Magnetism
Background:
- Femtosecond laser excitation of ferromagnetic metals generates ultrafast spin currents.
- These spin currents can affect magnetization dynamics, including demagnetization and transient magnetization enhancement.
Purpose of the Study:
- To analyze ultrafast magnetization dynamics in Ni/Ru/Fe and Ni/Ta/Fe layered structures.
- To investigate the influence of layer thicknesses, interlayers (Ru, Ta), and laser fluence on spin current effects.
Main Methods:
- Element- and femtosecond time-resolved X-ray Magnetic Circular Dichroism (XMCD).
- Systematic variation of Ni and Fe layer thicknesses, and interlayer materials (Ru, Ta).
- Control of pump laser fluence.
Main Results:
- Transient magnetization enhancement in Ni/Ru/Fe was not observed, contrary to previous findings.
- A reduced demagnetization of the Fe layer was observed in Ni/Ru/Fe compared to Ni/Ta/Fe.
- The spin-scattering Ta interlayer suppressed spin currents from Ni to Fe.
- Increasing Ni and Fe layer thicknesses decreased the effect of spin currents on the buried Fe layer, indicating a short spin current mean free path (few nm).
Conclusions:
- Ultrafast spin currents have a limited effect on buried layers due to their short mean free path.
- Sample design, particularly layer thickness and interface properties, must be optimized for efficient utilization of spin currents.
- Further research is needed to clarify the role of interfaces in ultrafast spin current dynamics.
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