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Description
Spin pumping is the transfer of angular momentum across interfaces
into a non-ferromagnetic material driven by the precessing magnetization
of an adjacent ferromagnet. Using ferromagnetic resonance
(FMR) the presence of spin pumping can be evidenced by an increase
of the Gilbert damping parameter 𝛼 [1]. Here we study Platinum-
Permalloy (Pt/Py) heterostructures using temperature-dependent
broadband FMR. A clear increase of 𝛼 is seen in a temperature
range from 10-300 K when Pt and Py are in direct contact. The
temperature dependence of the spin-pumping contribution can be
derived by comparing with an Al-sandwiched Py reference film from
[2]. Surprisingly, upon insertion of a thin Al spacer layer between
Pt and Py the increase in 𝛼 is suppressed. X-ray magnetic circular
dichroism at the Pt L$_3$-edge reveals a clear magnetic polarization in
Pt/Py whereas it is absent when a spacer layer of only 2 nm of Al is
inserted. The induced polarization of Pt can thus be associated with
spin pumping, while non-polarized Pt in proximity to Py shows an
almost identical 𝛼(𝑇) behavior as the Py reference sample in [2].
[1] Y. Tserkovnyak Phys. Rev. Lett. 88, 117601 (2002)
[2] V. Ney et al. Phys. Rev. Materials 7, 124403 (2023)