Spin Injection Enhancement via Normal Metal Funneling
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Solution Overview
Problem
Current technologies using high spin-orbit coupling materials for magnetization switching are limited by the maximum spin current density, which is constrained by the spin Hall angle, making it challenging to effectively switch ferromagnetic material polarity with smaller charge current density.
Innovation Solution
Incorporating a normal metal layer between the spin-orbit coupling and ferromagnetic layers, or a pure spin conductor layer between the spin-orbit coupling and ferromagnetic layers to funnel spins from a larger area into a smaller area, thereby reducing charge current shunting and enhancing spin current density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a spin-orbit coupling layer is used to induce transverse spin current density, then magnetization switching can be achieved, but the spin current density is limited by the spin Hall angle and cannot be sufficiently increased
Solution Approach 1:
The patent introduces a normal metal layer with larger in-plane area than the spin-orbit coupling layer, creating a geometric configuration where spin currents can diffuse laterally from the SOC layer into the NM layer and then be funneled into the FM layer. This dimensional expansion allows spin currents to accumulate and concentrate beyond the limitations imposed by the spin Hall angle in the original SOC layer configuration.
Solution Approach 2:
The normal metal layer serves as an intermediary between the spin-orbit coupling layer and the ferromagnetic layer. It receives spin currents from the SOC layer through spin-charge conversion, allows lateral diffusion and accumulation of spins, and then funnels them into the FM layer. This intermediary structure enables enhanced spin current density without being constrained by the spin Hall angle of the SOC material alone.
2Power
If the spin-orbit coupling layer area is reduced to concentrate spin current, then spin current density increases, but charge current shunting increases and reduces switching efficiency
Solution Approach 1:
The patent utilizes the normal metal layer's larger in-plane area to collect spin currents from a broader region of the spin-orbit coupling layer. This geometric arrangement allows spin currents to be gathered from multiple locations and funneled into a concentrated stream toward the ferromagnetic layer, achieving high spin current density at the FM interface without reducing the effective area for spin generation in the SOC layer.
Solution Approach 2:
The patent separates the functions of spin generation, spin transport, and spin injection into distinct layers. The spin-orbit coupling layer is dedicated to spin generation via the spin Hall effect, the normal metal layer handles spin transport and concentration through lateral diffusion, and the ferromagnetic layer receives the funneled spin current. This functional segmentation allows each layer to be optimized for its specific role without compromising overall efficiency.
3Power
If a normal metal layer is added to funnel spins, then spin current density is enhanced, but device complexity increases
Solution Approach 1:
The normal metal layer performs multiple functions simultaneously: it serves as a spin transport medium, a spin concentration reservoir, and a spin funneling channel. By making the NM layer serve these multiple purposes, the patent achieves enhanced spin current density without adding additional functional components, thereby limiting the increase in device complexity.
Solution Approach 2:
The patent merges the spin transport and spin concentration functions into a single normal metal layer rather than using separate layers for each function. This consolidation reduces the total number of interfaces and simplifies the device structure while still achieving the desired spin current enhancement through the combined effects of spin diffusion and geometric funneling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly increases the spin current density relative to the charge current density, achieving a higher effective spin Hall angle and improved switching efficiency, with the pure spin conductor layer providing up to 7 times enhancement in spin current density.
Implementation Method 1
a longitudinal charge current density (Jc) induces a transverse spin current density which if large enough can switch magnetization direction of a ferromagnet (FM)
Implementation Method 2
λg is the spin diffusion length
Data Source
AI summary
A switching device is disclosed. The switching device includes a spin-orbit coupling (SOC) layer, a pure spin conductor (PSC) layer disposed atop the SOC layer, a ferromagnetic (FM) layer disposed atop the PSC layer, and a normal metal (NM) layer sandwiched between the PSC layer and the FM layer. The PSC layer is a ferromagnetic insulator (FMI) is configured to funnel spins from the SOC layer onto the NM layer and to further provide a charge insulation so as to substantially eliminate current shunting from the SOC layer while allowing spins to pass through. The NM layer is configured to funnel spins from the PSC layer into the FM layer.