Temperature dependence of the anomalous Nernst coefficient for Ni80Fe20 determined with metallic nonlocal spin valves

Abstract

The anomalous Nernst effect, which generates an out-of-plane charge voltage in response to a thermal gradient perpendicular to the magnetization of a ferromagnet, can play a significant role in many spintronic devices where large thermal gradients exist. Since they typically include features deep within the submicron regime, nonlocal spin valves can be made very sensitive to this effect by lowering the substrate thermal conductance. Here, we use nonlocal spin valves suspended on thin silicon nitride membranes to determine the temperature dependence of the anomalous Nernst coefficient of 35 nm thick permalloy (Ni80Fe20) from 78 K to 300 K. In a device with a simple ferromagnet geometry, the transverse Seebeck coefficient shows a weak temperature dependence, with values at all T near 2.5 μV/K. Assuming previously measured values of the Seebeck coefficient for permalloy, which has a near-linear dependence on T, leads to a low temperature upturn in the anomalous Nernst coefficient RN. We also show that the temperature dependence of this coefficient is different when a constricted nanowire is used as the ferromagnetic detector element.

Magneto-thermoelectric effects mapping using tip-induced temperature gradient in atomic force microscopy

“…We estimate the magnitude of the ANE S ANE in the Py from the experimental results shown in Figure 2B and the simulation. Interestingly, the reported values of S ANE for Py vary significantly between 0.005-2.6 μV/K in the literature [7,[23][24][25][26][27]. Figure 3C shows the spatial distribution of the simulated vertical temperature gradient using the parameters G c = 20 μW/K, r c = 30 nm.…”

Thermal effects in spintronic materials and devices: An experimentalist’s guide

“…In such a case even the small thermal gradients I calculate here can drive large voltage contributions if the thin film is a conducting ferromagnet. I demonstrate this with the column labeled V ANE using values for the anomalous Nernst effect for Py, [34], which I will discuss in more detail in section 3.…”

“…The metallic ferromagnet that has the most measurements of the ANE coefficient (still only a handful) is permalloy, the Ni-Fe alloy with ∼ 80% Ni. Most values for S N fall near −2−3 µV/K, [34,[95][96][97][98][99], though some authors report much smaller values [100]. There are two more common approaches to measure the ANE for metals, one a variation of the experiment used to probe the longitudinal spin Seebeck effect (described in more detail below), and the second using nanoscale metallic devices called non local or lateral spin valves.…”

“…This effect adds a voltage signal proportional to the hysteresis of the FM (odd in field), and has been demonstrated many times and used to measure the ANE in several FM nanowires. [34,95,99,143,207] In addition to this field-dependent background effect, there are (in the simplest view) field-independent background contributions to the total measured voltage that arise from interaction of the induced thermal gradients and the Seebeck and Peltier effects. Figs.…”

Nanoscale Magnetization and Current Imaging Using Time-Resolved Scanning-Probe Magnetothermal Microscopy

“…To experimentally access these effects, we apply a pulsed laser, either directly focused or nanoconfined by the near-field tip, to create a transient local temperature increase, Δ T , and a corresponding local gradient ∇ T . The local magnetization m subjected to ∇ T generates an electric field E ANE through the anomalous Nernst effect (ANE), − with coefficient N . On the basis of the prior finite-element modeling for our materials and configuration, the vertical component of the thermal gradient dominates over the lateral component of the thermal gradient .…”