Thickness dependence on dynamical spin injection driven by thermal effects in CoFeB/Pt bilayer

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Dynamical spin injection in ferromagnetic metal (FM)/non-magnetic metal (NM) bilayers is typically explained by spin pumping at the interface.
• Thermal effects, including the spin (dependent) Seebeck effect (S(d)SE) driven by ferromagnetic resonance (FMR) heating, are also proposed contributors, especially within the FM layer away from the interface.

Purpose of the Study:

• To investigate the detailed mechanism of dynamical spin injection in CoFeB/Pt bilayer films.
• To accurately evaluate the CoFeB thickness dependence of the inverse spin Hall voltage by isolating contributions.
• To differentiate and quantify the roles of the spin Seebeck effect (SSE) and spin-dependent Seebeck effect (SdSE) in CoFeB/Pt bilayers.

Main Methods:

• Fabrication of CoFeB/Pt bilayer films with varying CoFeB thicknesses.
• Measurement of inverse spin Hall voltage.
• Subtraction of signals from single CoFeB layers to isolate bilayer interface effects.
• Analysis of diffusion properties to separate SSE and SdSE contributions.

Main Results:

• Dynamical spin injection and FMR heating effects exhibit significant dependence on CoFeB layer thickness.
• The contribution of the spin Seebeck effect (SSE) was found to be larger than that of the spin-dependent Seebeck effect (SdSE) in the studied CoFeB/Pt bilayer films.
• Accurate evaluation of thickness-dependent inverse spin Hall voltage was achieved by accounting for single-layer signals.

Conclusions:

• Both spin pumping and thermal effects contribute to dynamical spin injection in CoFeB/Pt bilayers.
• The spin Seebeck effect plays a more dominant role than the spin-dependent Seebeck effect in generating spin currents within these specific bilayer structures.
• Understanding these contributions is crucial for optimizing spintronic devices that utilize spin current generation and detection.