Enhancement of Spin Injection in Metallic Nonlocal Spin Valves on Silicon Nitride Membranes*

Nonlocal spin valves (NLSVs) are an important tool for both applied and fundamental research in nanomagnetism due to their unique ability to separate charge and spin currents.[1,2] Previous research shows that changes to the composition of the NLSV substrate can have a marked effect on the background nonlocal resistance by changing the substrate thermal conductance,[3] and our research demonstrates enhancement of nonlocal spin resistance by the anomalous Nernst effect (ANE).[4]

We present dramatically lowered thermal conductance in NLSVs fabricated on SiN membranes as evidenced in large background signals compared to substrate devices. We also present evidence of increased ANE due to geometric confinement of the thermal gradient. 2D finite-element analysis shows a Nernst coefficient of 0.5, nearly 4 times the literature value. This implies that our assumption of a Seebeck coefficient for permalloy of -12 microV/K at 200 K may be incorrect. Finally, we present evidence that the sign of the nonlocal spin resistance changes at higher temperatures, indicating the need for further thermal simulations.

[1] Jedema, et al. Nature 410, 345 (2001)
[2] Ji, et al. APL 88, 052509 (2006)
[3] Kasai, et al. APL 104, 162410 (2014)
[4] Hojem, et al. (in preparation)