Effect of Grain Size on the Microwave Properties of Polycrystalline Yttrium Iron Garnet
- 15 March 1970
- journal article
- research article
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 41 (4), 1637-1641
- https://doi.org/10.1063/1.1659084
Abstract
Data on the parallel pump and subsidiary absorption threshold at 9.1 GHz and effective linewidth ΔHeff at 9.9 GHz have been obtained for polycrystalline YIG materials with an average grain diameter a0 from 1 to 30 μ. The fine‐grain samples (1–10 μ) were made by hot pressing. The parallel pump spin‐wave line‐widths extrapolated to zero wavenumber, ΔHk→0, vary as a0−1, with ΔHk→0=25 Oe at a0=1 μ. The ΔHk for the fine‐grain samples (a0 ≈ 1 μ) show an inverse k‐dependence. A simple model in which the spin‐wave transit time across individual grains limits ΔHk appears to explain the a0−1 dependence but not the observed k‐dependences for ΔHk. The high‐field ΔHeff is 5.5 Oe for a0=1 μ and varies as a0−1/2. The low‐field values are slightly larger, due to a small two‐magnon contribution arising from coupling to degenerate short‐wavelength spin waves. Even though the high‐field ΔHeff contains no two‐magnon contribution, it is significantly larger than linewidths in single crystals. A recently proposed magnetostriction mechanism is consistent with the a0−1/2 dependence, but the predicted magnitude of ΔHeff is much smaller than observed.Keywords
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