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Spin-orbit torques in normal metal/Nb/ferromagnet heterostructures
Min Hyeok Lee1, Gyungchoon Go2, Yong Jin Kim1
1Department of Materials Science and Engineering, Korea University, Seoul, 02841, Republic of Korea.
Scientific Reports
|October 27, 2021
Summary
Investigating niobium (Nb) thickness effects on spin-orbit torque (SOT) efficiency reveals distinct behaviors in Ta/Nb/CoFeB and Pt/Nb/CoFeB heterostructures. The SOT polarity reversal observed in Pt/Nb/CoFeB, unlike in Ta/Nb/CoFeB, highlights the impact of differing spin-orbit coupling signs.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Spintronics
Background:
- Spin-orbit torque (SOT) efficiency is critical for understanding spintronic devices.
- Layer thickness significantly influences SOT properties in heterostructures.
- Niobium (Nb) is explored as a layer in SOT devices.
Purpose of the Study:
- To quantify the Nb-thickness-dependent SOT efficiency in Ta/Nb/CoFeB and Pt/Nb/CoFeB heterostructures.
- To elucidate the physical mechanisms behind varying SOT behavior with Nb thickness.
- To determine the spin diffusion length of Nb in these specific material systems.
Main Methods:
- Fabrication of Ta/Nb/CoFeB and Pt/Nb/CoFeB layered heterostructures with varying Nb thicknesses.
- Measurement of SOT efficiency as a function of Nb layer thickness.
- Current-induced SOT switching experiments to observe polarity changes.
- Extraction of spin diffusion length for Nb in each heterostructure.
Main Results:
- Nb thickness dependence of SOT efficiency differs significantly between Ta/Nb/CoFeB and Pt/Nb/CoFeB.
- Pt/Nb/CoFeB exhibits SOT sign reversal with Nb thickness due to opposing spin-orbit coupling signs of Pt and Nb.
- Ta/Nb/CoFeB does not show polarity reversal, consistent with the same spin-orbit coupling signs of Ta and Nb.
- Spin diffusion lengths for Nb were successfully extracted for both heterostructure types.
Conclusions:
- The interplay between layer thickness and material-specific spin-orbit coupling dictates SOT efficiency and polarity.
- These findings offer a systematic understanding of material- and thickness-dependent SOT characteristics.
- The results are crucial for designing and optimizing spintronic devices based on SOT.
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