Experimental test of the spin mixing interface conductivity concept (1306.5012v1)

Abstract: We perform a quantitative, comparative study of the spin pumping, spin Seebeck and spin Hall magnetoresistance effects, all detected via the inverse spin Hall effect in a series of over 20 yttrium iron garnet/Pt samples. Our experimental results fully support present, exclusively spin current-based, theoretical models using a single set of plausible parameters for spin mixing conductance, spin Hall angle and spin diffusion length. Our findings establish the purely spintronic nature of the aforementioned effects and provide a quantitative description in particular of the spin Seebeck effect.

• The paper demonstrates that spin mixing conductance reliably predicts spintronic phenomena across diverse experimental conditions using over 20 YIG/Pt samples.
• It employs FMR techniques to measure spin current density, spin Hall angle (0.11), and spin diffusion length (1.5 nm), aligning results with established theoretical models.
• The findings reinforce the spintronic basis of phenomena like spin pumping, the spin Seebeck effect, and SMR, paving the way for advanced device engineering.

Analyzing the Spin Mixing Interface Conductivity Concept: Insights from Experimental Evaluations

This paper presents a comprehensive experimental investigation aimed at validating the concept of interface spin mixing conductivity through the examination of various spin-related phenomena, including spin pumping, the spin Seebeck effect, and spin Hall magnetoresistance (SMR), all observed via the inverse spin Hall effect. The research utilizes over 20 yttrium iron garnet (YIG)/Pt samples for a thorough comparative analysis.

The authors provide a quantitative alignment of their experimental findings with existing theoretical models that rely on spin current mechanisms, employing a consistent set of parameters: spin mixing conductance, spin Hall angle, and spin diffusion length. Notably, the empirical data substantiate the spintronic nature of the examined phenomena, offering a solid basis for the spin Seebeck effect.

Methodology and Results

1. Spin Pumping: Utilizing ferromagnetic resonance (FMR) techniques, spin pumping was investigated by subjecting YIG/Pt bilayers to microwave radiation, resulting in the generation of a spin current. The spin current, identified through the inverse spin Hall effect, confirmed the theoretical predictions using the established models. The paper determined the spin current density $J_s$ derived from the relationship $J_s = \frac{g_{\uparrow \downarrow}}{2 \pi} E$, with $E$ representing relevant excitation energy sources.
2. Spin Seebeck Effect: This effect was examined using a thermal gradient across YIG/Pt interfaces. The experimental outcomes supported the description of $J_s$ again being proportional to an associated energy parameter, evidencing that pure spin currents are responsible for the thermal excitations observed.
3. Spin Hall Magnetoresistance: The SMR effect was characterized by measuring changes in electrical resistance induced by the alignment of applied spin currents in Pt. The results were consistent with spin-polarized currents affecting magnetoresistance, thus validating existing theories around the SMR mechanism.

The paper highlights the effective spin mixing conductance, $g_{\uparrow \downarrow}$, as consistent across experimental conditions, averaging $1 \times 10^{19} \, \text{m}^{-2}$. The spin Hall angle $\alpha_{SH}$ and the spin diffusion length $\lambda_{SD}$ were found to be 0.11 and 1.5 nm respectively, which align with previously reported data, providing further credence to the results.

Implications and Future Directions

The findings emphasize the robustness of the spin mixing conductance model as a unified descriptor for spintronic phenomena across different experimental settings. The demonstration that spin pumping, spin Seebeck effect, and SMR can be quantitatively described using singular, consistent parameters solidifies their foundation in pure spin current physics. Furthermore, this paper refutes possible alternate explanations, such as static proximity polarization in Pt, cementing the spintronic basis of these effects.

The nuanced understanding gained through these experiments enhances the potential for practical applications, especially in the design and development of spintronic devices utilizing interface phenomena. Furthermore, the paper opens pathways for future research into hybrid systems where interfacial properties could be engineered for optimized spintronic performance.

Conclusion

This research provides a vital experimental confirmation of the theoretical frameworks governing spin currents, emphasizing the central role of interface spin mixing conductance. The ability to use a unified parameter set across varied experimental manipulations of spin dynamics strengthens the conceptual underpinnings of spintronics and paves the way for further explorations and technological advancements in this domain.