Robust longitudinal spin-Seebeck effect in Bi-YIG thin films

Abstract

In recent years, the coupling of magnetic insulators (bismuth-doped yttrium iron garnet, Bi-YIG) with platinum has garnered significant interest in spintronics research due to applicability as spin-current-driven thermoelectric coatings. These coatings bridge the gap between spintronics technologies and thermoelectric materials, providing a novel means of transforming waste heat into electricity. However, there remain questions regarding the origins of the spin-Seebeck effect (SSE) as well as claims that observed effects are a manifestation of magnetic proximity effects, which would induce magnetic behavior in platinum. Herewith we provide support that the voltages observed in the Bi-YIG/Pt films are purely SSE voltages. We reaffirm claims that magnon transport theory provides an ample basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed-laser deposition, as these Bi-YIG films possess large SSE voltages (even in absence of an external magnetic field), as much as twice those of films fabricated via solution-based methods.

Observation of longitudinal spin-Seebeck effect in cobalt-ferrite epitaxial thin films

“…In contrast, the nearly closed V LSSE -H curve for the Pt/CFO sample B results in large reduction of the TE output at H = 0 kOe. The above experimental results demonstrate that the external-field-free TE generation based on the LSSE can be realized by applying strain to MIs without the aid of undulated film surfaces 29 or particular crystal axis. 14 This feature may further expand the versatility of MI-based TE devices.…”

“…Consequently, this highly-anisotropic spinel ferrite exhibits high squareness in voltage-field hysteresis loops and relatively large TE outputs even at zero external field with the help of the strain, but without the undulation of film surfaces 29 or particular crystal axes. 14 The processes of sample preparation are as follows.…”

Thermodynamic transport theory of spin waves in ferromagnetic insulators

“…In the LSSE a spin current is generated by a temperature gradient in a ferrimagnetic insulator like yttrium iron garnet (YIG) and it is detected by the inverse spin Hall effect in an adjacent Pt layer [5][6][7][8][9] . This effect has been interpreted as the consequence of the presence of a spin current carried by non equilibrium spin waves (or magnons) in the ferrimagnetic insulator which is converted into a spin current carried by electrons in the metal 3,10,11 . The source of this conversion is the interaction between the d electrons in the ferromagnet and the s electrons in the metal which gives rise to an absorption of a magnon in the insulator and the corresponding generation of an electron spin flip in the metal [12][13][14][15][16][17][18] .…”

Picosecond Spin Seebeck Effect

“…The symmetry of the resulting voltage signal with respect to the direction of the applied magnetic field is used as an indication of the ISHE. ISHE-based LSSE measurements have been reported for various insulators, e.g., ferrimagnetic garnets such as Y 3 Fe 5 O 12 (YIG) [14], Bi-substituted YIG [15] [24]. The experiments are typically reported as observations of the LSSE.…”