Spin‐Thermoelectric Generation Associated with Magnetization Dynamics in the Insulator‐Based Generators Fabricated from Liquid Phase Epitaxial Yttrium Iron Garnet, Bi‐Substituted YIG and Bi‐ and Al‐Substituted YIG Films

• Published in: IEEJ transactions on electrical and electronic engineering 2024-11, Vol.19 (11), p.1770-1780
• Main Authors: Imamura, Masaaki, Asada, Hironori, Matsuda, Ryota, Tashima, Daisuke, Kitagawa, Jiro
• Format: Article
• Language: English
• Subjects: Damping; domain magnetization processes of YIG; Electric potential; Energy transfer; Epitaxial growth; Ferromagnetic materials; Ferromagnetic resonance; Generators; Hall effect; Induced magnetic anisotropy; Iron; Liquid phase epitaxy; Liquid phases; Magnetization; single crystal YIG films; Single crystals; spin caloritronics; Spin dynamics; Spin exchange; Spin-orbit interactions; spin‐thermoelectric generation; Substitutes; Thermal energy; Thermoelectricity; Voltage; Yttrium-iron garnet
• ISSN: 1931-4973; 1931-4981
• DOI: 10.1002/tee.24137

An insulator‐based spin‐thermoelectric (STE) generator is composed of a thin paramagnetic metal (PM: Pt) layer for generating the STE voltage VSTE via the inverse spin Hall effect and a ferrimagnetic insulator (FMI) film or slab used for producing spin‐wave spin currents due to a temperature gradient ∇T$$ \nabla T $$. Yttrium iron garnet (YIG) is a key material used for the FMI of STE generators. We examined in detail the ferromagnetic resonance (FMR) properties of YIG (Y3Fe5O12), Bi‐substituted YIG (Y3‐xBixFe5O12) and Bi‐ and Al‐substituted YIG (Y3‐xBixFe5‐yAlyO12) films grown by liquid phase epitaxy (LPE). Bi‐substituted YIG films exhibited the large FMR damping and high STE voltage when the films were incorporated in the STE generator. The LPE‐grown Y2.35Bi0.65Fe5O12 film exhibited the FMR linewidth ΔH of 30 mT and the VSTE of 70 μV for the ∇T of 90×10−3°C/μm$$ 90\times {10}^{-3{}^{\circ}}C/\upmu \mathrm{m} $$. This paper comprehensively presents the origin of the STE generation in the insulator‐based generators on the basis of the results of FMR and STE measurements. To clarify the origin of STE generation in the generators fabricated from single crystal YIG (YIG, Bi‐substituted YIG and Bi‐ and Al‐substituted YIG) films grown by LPE, three principal factors are explained: (a) thermal energy transfer from the phonon system to the spin system, which strengthens the heat excitation of spin precession, through the spin–orbit coupling enhanced by the growth‐induced magnetic anisotropy of LPE‐grown YIG films, (b) in the YIG films incorporated in the STE generators, the generation of spin‐wave spin currents owing its origin to the ferromagnetic spin exchange interaction acting between neighboring spins due to ∇T$$ \nabla T $$, and (c) how the spin currents pumped into the Pt layer from the YIG film at the Pt/YIG bilayer interface are affected by the magnetization processes of single crystal YIG films. It is concluded that the STE generation of insulator‐based STE generators can be explained from a viewpoint of the spin dynamics under the effect of ∇T$$ \nabla T $$ in the Pt/YIG bilayer structure. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.