Length Scale of the Spin Seebeck Effect

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• The spin Seebeck effect (SSE) is a key phenomenon in spintronics, converting heat gradients into spin currents.
• Understanding the origin of SSE, whether interfacial or bulk, is crucial for device applications.
• Yttrium iron garnet (YIG) is a promising material for SSE studies due to its low damping and insulating properties.

Purpose of the Study:

• To investigate the origin of the longitudinal spin Seebeck effect (LSSE) in yttrium iron garnet (YIG).
• To determine the influence of film thickness and temperature on LSSE amplitude.
• To differentiate between interfacial and bulk contributions to the SSE in YIG.

Main Methods:

• Fabrication of YIG films with thicknesses ranging from 20 nm to 50 μm.
• Measurement of LSSE at room temperature and 50 K.
• Comparison of experimental results with numerical simulations of thermal magnonic spin currents.

Main Results:

• LSSE amplitude increases with YIG film thickness, saturating at a critical thickness.
• The critical thickness for saturation increases with decreasing temperature.
• Observed thickness dependence aligns with simulations of bulk magnonic spin currents, not interface effects.

Conclusions:

• The spin Seebeck effect in YIG predominantly originates from bulk magnonic spin currents.
• The finite magnon propagation length governs the thickness dependence of LSSE.
• This study provides insights into the thermal transport of magnons in insulating ferrimagnets.