Reproducible low Gilbert damping yttrium iron garnet by magnetron sputtering

Abstract

Reproducible growth of single-crystalline (111) yttrium iron garnet (YIG) with very low Gilbert damping (α) has been reported by the use of several techniques, and continues to attract the attention of many groups in sprintronics and magnonics. We report on the growth of YIG thin films onto GGG (111) substrates by magnetron sputtering, followed by an ex-situ oxygen flow heat treatment. The magnetic properties were studied by ferromagnetic resonance, and the structural and morphological properties by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. The annealing parameters and thickness dependency on the magnetic properties was systematically investigated. A decrease in α for almost ten times was found preventing the YIG growth at the edges of the substrate by the use of lithography. For YIG 60 nm thick α were measured as (1.72 ± 0.08) × 10−4, Ms = 179 ± 2 emu cm−3, and surface roughness as 0.23 nm. To quantify the growth as being of good quality, we measured the spin current injection via spin pumping to an adjacent bismuth-doped copper layer with spin mixing conductance g↑↓ = 2.16 × 1018 m−2, for a platinum layer g↑↓ = 2.17 × 1018 m−2, with the detection of a 7 μV in the inverse spin Hall effect voltage, quantities which are in good agreement with the best values reported so far.