Temperature dependent relaxation of dipole-exchange magnons in yttrium iron garnet films

TL;DR

This study investigates how the relaxation rates of magnons in yttrium iron garnet (YIG) films vary with temperature, revealing a significant increase in relaxation rate below 150 K due to impurities and substrate effects, which impacts magnonic applications.

Contribution

It provides the first detailed experimental analysis of temperature-dependent magnon relaxation in YIG films across a wide temperature range, highlighting impurity effects.

Findings

Magnon relaxation rate increases significantly below 150 K in YIG films.

Impurities and substrate coupling contribute to relaxation behavior at low temperatures.

Bulk YIG crystal shows different relaxation characteristics compared to films.

Abstract

Low energy consumption enabled by charge-free information transport, which is free from ohmic heating, and the ability to process phase-encoded data by nanometer-sized interference devices at GHz and THz frequencies are just a few benefits of spin-wave-based technologies. Moreover, when approaching cryogenic temperatures, quantum phenomena in spin-wave systems pave the path towards quantum information processing. In view of these applications, the lifetime of magnons$-$spin-wave quanta$-$is of high relevance for the fields of magnonics, magnon spintronics and quantum computing. Here, the relaxation behavior of parametrically excited magnons having wavenumbers from zero up to $6\cdot 10^5 \mathrm{rad~cm}^{-1}$ was experimentally investigated in the temperature range from 20 K to 340 K in single crystal yttrium iron garnet (YIG) films epitaxially grown on gallium gadolinium garnet (GGG) substrates as well as in a bulk YIG crystal$-$the magnonic materials featuring the lowest magnetic damping known so far. As opposed to the bulk YIG crystal in YIG films we have found a significant increase in the magnon relaxation rate below 150 K$-$up to 10.5 times the reference value at 340 K$-$in the entire range of probed wavenumbers. This increase is associated with rare-earth impurities contaminating the YIG samples with a slight contribution caused by coupling of spin waves to the spin system of the paramagnetic GGG substrate at the lowest temperatures.