Thermal spin injection and interface insensitivity in permalloy/aluminum metallic non-local spin valves

We present measurements of thermal and electrical spin injection in nanoscale metallic non-local spin valve (NLSV) structures. Informed by measurements of the Seebeck coefficient and thermal conductivity of representative films made using a micromachined Si-N thermal isolation platform, we use simple analytical and finite element thermal models to determine limits on the thermal gradient driving thermal spin injection and calculate the spin dependent Seebeck coefficient to be $-0.5\ \mu\mathrm{V}/\mathrm{K}< S_{s}<-1.3\ \mu\mathrm{V}/\mathrm{K}$. This is comparable in terms of the fraction of the absolute Seebeck coefficient to previous results, despite dramatically smaller electrical spin injection signals. Since the small electrical spin signals are likely caused by interfacial effects, we conclude that thermal spin injection is less sensitive to the FM/NM interface, and possibly benefits from a layer of oxidized ferromagnet, which further stimulates interest in thermal spin injection for applications in sensors and pure spin current sources

Track A Basic Science

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd

Thermal Spin Injection and Interface Insensitivity in Permalloy/Aluminum Metallic Nonlocal Spin Valves

We present measurements of thermal and electrical spin injection in nanoscale metallic nonlocal spin valve structures. Informed by measurements of the Seebeck coefficient and thermal conductivity of representative films made using a micromachined Si-N thermal isolation platform, we use simple analytical and finite-element thermal models to determine limits on the thermal gradient driving thermal spin injection and calculate the spin-dependent Seebeck coefficient to be −0.5μV/K\u3eSs\u3e−1.6μV/K. This is comparable in terms of the fraction of the absolute Seebeck coefficient to previous results, despite dramatically smaller electrical spin injection signals. Since the small electrical spin signals are likely caused by interfacial effects, we conclude that thermal spin injection is less sensitive to the ferromagnetic/nonmagnetic interface, and possibly benefits from the presence of oxidized ferromagnets, which further stimulates interest in thermal spin injection for applications in sensors and pure spin current sources

Thermal Gradients and Anomalous Nernst Effects in Membrane-supported Nonlocal Spin Valves

Metallic nonlocal spin valves (NLSVs) are important in modern spintronics due to their ability to separate pure spin current from charge current. These metallic nanostructures, often constructed from features with widths in the deep submicron regime, generate significant thermal gradients in operation, and the heat generated has important consequences for spin injection and transport. We use e-beam nanolithography to manufacture NLSVs with Ni-Fe alloy ferromagnetic nanowires and aluminum spin channels on 500-nm silicon nitride (Si-N) membranes to lower the thermal conductance of the substrate dramatically. While this extreme example of thermal engineering in a spintronic system increases the background nonlocal signals in ways expected based on earlier work, it also enhances thermoelectric effects, including the anomalous Nernst effect, and reveals a previously unknown thermally assisted electrical spin injection that results from a purely in-plane thermal gradient. We examine these effects as a function of temperature and, by careful comparison with 2D finite element models of the thermal gradients calculated at a single temperature, demonstrate that the anomalous Nernst coefficient of the 35-nm-thick Ni-Fe alloy, RN=0.17 at T=200K, is in line with the few previous measurements of this effect for thin films