Antiferromagnonic Spin Transport from Y$_3$Fe$_5$O$_{12}$ into NiO (1509.04337v1)

Abstract: We observe highly efficient dynamic spin injection from Y$3$Fe$_5$O${12}$ (YIG) into NiO, an antiferromagnetic (AF) insulator, via strong coupling, and robust spin propagation in NiO up to 100-nm thickness mediated by its AF spin correlations. Strikingly, the insertion of a thin NiO layer between YIG and Pt significantly enhances the spin currents driven into Pt, suggesting exceptionally high spin transfer efficiency at both YIG/NiO and NiO/Pt interfaces. This offers a powerful platform for studying AF spin pumping and AF dynamics as well as for exploration of spin manipulation in tailored structures comprising metallic and insulating ferromagnets, antiferromagnets and nonmagnetic materials.

Insights into Spin Transport in Antiferromagnetic Insulators

The research conducted by Hailong Wang and colleagues offers a significant examination of spin transport phenomena in antiferromagnetic (AF) insulators, specifically focusing on NiO. By exploring the dynamic spin injection from Y$_3$Fe$_5$O$_{12}$ (YIG) into NiO and subsequently into Pt, the paper challenges preconceptions about AF materials' capabilities in supporting spin transport. Notably, this paper investigates the interplay between ferromagnetic (FM) YIG, AF NiO, and nonmagnetic Pt, establishing a robust framework for understanding spin dynamics in heterogeneous magnetic structures.

Numerical Findings and Observations

The results highlight the high efficiency of spin transport across NiO up to a thickness of 100 nm, enhanced by AF spin correlations within NiO. Critical to understanding spin transfer efficiency, the paper reports enhanced spin currents at the YIG/NiO and NiO/Pt interfaces. Specifically, the introduction of a thin NiO layer significantly amplifies the spin pumping signals compared to direct YIG/Pt interfaces, with observed increases in the Inverse Spin Hall Effect (ISHE) voltages by factors of 1.55, 1.99, and 7.05, for different YIG samples.

The detailed paper of the dependency of spin current generation as a function of NiO thickness reveals several key findings. Firstly, ISHE voltages initially increase with NiO thickness, peaking at around 2 nm before exhibiting an exponential decay, suggestive of diffusive spin transport mechanisms within the AF insulator. The diffusion lengths of spin magnons or AF-mediated spin fluctuations within NiO are estimated to be approximately 8.8 nm to 11 nm. This decay regime hints at the role of AF magnons or dynamic AF correlations in facilitating spin transport.

Furthermore, the exchange coupling at YIG/NiO induces notable effects on damping within YIG, as evidenced by the increase in full-width at half-maximum (FWHM) linewidths with NiO thickness. This finding is consistent with the theoretical understanding of exchange coupling-induced damping in FM/AF bilayer systems.

Implications for Spintronics and Future Research

This research provides crucial insights into the mechanisms of spin transport in heterogeneous structures involving AF insulators. The findings have significant implications for spintronics, particularly in the development of devices that leverage high-efficiency spin transport mechanisms without relying solely on ferromagnetism. The reported spin transport efficiency via AF magnons or fluctuations unlocks new pathways for integrating AF materials in spintronic devices, enhancing their performance.

The paper also prompts further research into the engineering of heterostructures with FM, AF, and nonmagnetic (NM) materials. Understanding the interfacial dynamics and spin conversion efficiencies at these interfaces suggests future work could focus on optimizing materials and interfaces for specific applications in spintronic technology.

In conclusion, the work by Wang et al. contributes significantly to the understanding of spin transport in antiferromagnetic insulators. By demonstrating spin transfer efficiencies in complex magnetic heterostructures, it paves the way for novel approaches in designing advanced spintronic devices that utilize the peculiar properties of antiferromagnetic materials. Future studies could focus on exploring other AF materials and even hybrid systems to further generalize and apply these findings in practical applications.