Magneto-thermal transport behavior in freestanding Ni80Fe20/Au bilayer thin films

Abstract

Spin polarization, when induced in a non-ferromagnetic material, can change the underlying material behavior especially if the spin diffusion length is of the same order as the sample dimension such as thickness. In this study, we experimentally demonstrate thermal hysteretic behavior induced by spin polarization in Ni80Fe20 (10 nm)/Au (100 nm) bilayer freestanding sample. The thermal hysteresis behavior is uncovered using magneto thermal characterization based on self-heating 3ω method. The third harmonic voltage shows diverging behavior and thermal hysteresis during cooling and heating of the sample under an applied magnetic field, which is attributed to the spin accumulation. The spin accumulation and thermal hysteresis in Au occurs due to ferromagnetic proximity polarization from Ni80Fe20 layer. The observed hysteresis behavior is also attributed to freestanding thin film structure and absence of substrate effects leading to longer spin diffusion length. This study demonstrates experimental evidence of ferromagnetic proximity polarization and resulting changes in thermal transport behavior in Au thin films.