Observation of the Planar Nernst Effect in Permalloy and Nickel Thin Films with In-Plane Thermal Gradients
Matthew R. Pufall, Azure Avery, Barry L. Zink
We present experimental evidence of a transverse thermopower, or planar Nernst effect, in ferromagnetic metal thin films driven by thermal gradients applied in the plane of the films. Samples of 20 nm thick Ni and Ni80-Fe20 were deposited on 500 nm thick suspended Si-N thermal isolation platforms with integrated platinum strips designed originally to allow measurement of thermally generated spin currents (the spin Seebeck effect). The low thermal conductivity of the thin supporting Si-N structure results in an essentially 2-D geometry that approaches the zero substrate limit, dramatically reducing the contribution of thermal gradients perpendicular to the sample plane typically found in similar experiments on bulk substrates. The voltage on the platinum strips generated transverse to the applied thermal gradient (VT ) is linear with increasing 4T and exhibits a sign reversal on hot and cold sides of the sample. However, VT is always even in applied magnetic field and shows a sin✓cos✓ angular dependence, both key indicators of the planar Nernst effect. The upper limit on the spin Seebeck coefficient, which would cause a signal with a cos ✓ angular dependence, in our experiment is on the order 10−12 V/K, at least an order of magnitude smaller than reported in experiments on similar samples on bulk substrates.
, Avery, A.
and Zink, B.
Observation of the Planar Nernst Effect in Permalloy and Nickel Thin Films with In-Plane Thermal Gradients, Physical Review Letters, [online], https://doi.org/10.1103/PhysRevLett.109.196602
(Accessed September 29, 2023)