Optically generated spin currents in platinum/magnetic insulator bilayer structures*

The generation and detection of pure spin current provides a pathway for solid-state devices to avoid Joule heating losses arising in electrical architectures.
Despite the promise of loss-free, spin-based devices, integrated spin current technology into real-world applications has proven difficult.
Here, we use a Pt/Y$_3$Fe$_5$O$_{12}$ (YIG) bilayer device to detect light from 390 nm to 2200 nm using the spin Seebeck effect (SSE).
We find that the nanometer-thick platinum layer is crucial for both spin current generation and detection.
We use a phase-sensitive, field-modulation technique to determine the temperature gradient across the YIG, $\nabla T$, created by optical illumination, $I$, to be $\nabla T/I = 0.0975 ^{\circ}$C$\cdot$m/W.
From our measured values of $\nabla T$ and $\nabla V$, we obtain the SSE coefficient of YIG to be $S_{\rm spin} = -\nabla V/\nabla T = -1.1$ nV/K; this value is consistent with reported literature values for other SSE materials.
This work reveals the possibility of using spin current generation and detection for broadband light optoelectronics.