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Wave-Number-Dependent Gilbert Damping in Metallic Ferromagnets
Y Li1, W E Bailey1
1Materials Science and Engineering, Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
Physical Review Letters
|April 2, 2016
Summary
Researchers measured wave-number-dependent Gilbert damping in NiFe, Co, and CoFeB films. Results support a new k-squared term in magnetization dynamics, distinct from spin pumping, with implications for spintronic devices.
Area of Science:
- Condensed Matter Physics
- Materials Science
Background:
- A novel wave-number-dependent dissipative term for magnetization dynamics in ferromagnetic metals has been proposed.
- This term mirrors the conservative exchange term and aims to refine models of magnetic damping.
Purpose of the Study:
- To experimentally investigate and quantify wave-number-dependent Gilbert damping in metallic ferromagnets.
- To validate the existence of a k-squared term in Gilbert damping and differentiate it from other damping mechanisms.
Main Methods:
- Measurements of wave-number-dependent Gilbert damping were performed using perpendicular spin wave resonance up to 26 GHz.
- Three metallic ferromagnets (NiFe, Co, CoFeB) were studied in thin film form to minimize eddy-current effects.
Main Results:
- Size effects in the thinnest films provided evidence for a k-squared dependence in Gilbert damping for low-order spin wave modes.
- The extracted magnitude of the k-squared term (A_k* = 0.08–0.1 nm²) was found to be an order of magnitude smaller than in previous studies on patterned elements.
- Higher-order modes in thicker films did not exhibit enhanced damping, likely due to conductivity and broadening effects.
Conclusions:
- The experimental results support the existence of a wave-number-dependent dissipative term (k-squared) in Gilbert damping for metallic ferromagnets.
- This k-squared damping is distinct from interfacial damping (spin pumping) and offers a more nuanced understanding of magnetization dynamics.
- The findings provide crucial parameters for designing and optimizing spintronic devices by controlling damping in magnetic materials.
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