Spintronics, the field that harnesses the spin of electrons to develop next-generation electronic devices, has been the focus of intense research in recent years. A group of scientists has made a significant breakthrough in understanding the mechanisms behind the generation of spin currents, which are the key to the operation of spintronic devices. Their study, published in the journal Scientific Reports, delves into the intricate relationship between thermal effects and the dynamical spin injection in a CoFeB/Pt bilayer system.
The Importance of Spin Currents in Spintronics
Spin currents, the flow of spin-angular momentum, are crucial for the development of spintronic devices, which promise ultra-low power consumption and enhanced data processing capabilities compared to traditional electronic devices. Researchers have been exploring various methods to generate and manipulate spin currents, including the use of ferromagnetic resonance (FMR), which can lead to the injection of spin currents through a process known as dynamical spin injection.
Unraveling the Mechanisms of Dynamical Spin Injection
In this study, the researchers have focused on understanding the detailed mechanisms behind dynamical spin injection in a CoFeB/Pt bilayer system. They discovered that in addition to the well-known spin pumping effect at the interface, thermal effects, such as the spin Seebeck effect (SSE) and the spin-dependent Seebeck effect (SdSE), also play a significant role in the generation of spin currents.
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Comprehensive Experimental Approach
The researchers employed a unique experimental approach to isolate and quantify the contributions of these different mechanisms. They first measured the FMR signals in a CoFeB single-layer system and then subtracted these signals from the measurements of the CoFeB/Pt bilayer system. This allowed them to eliminate the unwanted contributions from the CoFeB layer and focus on the pure inverse spin Hall effect (ISHE) signal, which is directly related to the dynamical spin injection.
Unveiling the Thickness Dependence
By systematically varying the thickness of the CoFeB layer, the researchers were able to investigate the thickness dependence of the dynamical spin injection. They found that the thermal contributions from SSE and SdSE were the dominant factors in determining the thickness dependence, while the spin pumping effect remained relatively constant.
Fig. 3
Separating the Contributions of SSE and SdSE
To further understand the role of thermal effects, the researchers separated the contributions of SSE and SdSE by leveraging their different diffusion properties. They determined that the magnon diffusion length in the CoFeB layer is around 7.7 nanometers, while the electron diffusion length is approximately 4.5 nanometers. This analysis revealed that the SSE contribution is larger than the SdSE contribution in the CoFeB/Pt system.
Implications and Future Directions
The findings of this study represent a significant advancement in the understanding of dynamical spin injection and its underlying mechanisms. By elucidating the interplay between spin pumping and thermal effects, the researchers have provided crucial insights that can guide the development of more efficient spintronic devices. Future research directions may involve exploring the influence of interfacial properties and investigating alternative material systems, such as those incorporating insulating layers, to further refine the understanding of spin current generation and transport.
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This article is based on research by Sora Obinata, Troy Dion, Riku Iimori, Takashi Kimura.
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