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Damped surface modes in thick YIG epilayers which appear at low fields close to the Damon-Eshbach limit in microwave spectra with the dc magnetic field parallel to the surface have been investigated. The results are explained in terms of the De Warnes-Wolfram model, when a surface anisotropy energy due to the effect of a diffusion layer on the spins at the substrate/film interface is taken into account. In accordance with the experimental results, the above theoretical assumption leads to a low value of the parallel wave vector ky for which those modes can be excited ( S 10 3 cm -I ). PACS numbers: 68.90. + g, 68.30. + z, 75.1O.Dg [This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 65.39.42.160 On: Mon, 08 Dec 2014 23:23:45

Ca-doped YIG films having composition Y3−x3+ Cax2+ Fe3+5−x Fex4+ O1 2 have been grown with a value of x = 0.25 and thickness 1.15 μm. Upon annealing in saturated FeCl2 solution, oxygen vacancies are introduced, which compensate for Ca2+ ions and reduce Fe4+ ions to Fe3+ ions. The uniaxial anisotropy constant changed from −5.89×103 erg/cm3 to −17.0×103 erg/cm3, which is consistent with a change in the crystal field effects reduction as proposed by Stacy and Rooymans. The exchange stiffness coefficient changed from 3.19×10−7 erg/cm to 3.66×10−7 erg/cm. The exchange stiffness parameter and the anisotropy energy have been studied as a function of temperature and oxygen vacancy concentration.

Longitudinal imaginary susceptibilities ∥χ″ in the spin-wave instability region were measured in YIG samples having bimodally distributed grain sizes. The samples were prepared by hot pressing mixtures of powders having grain sizes x of 1 and 10 μ. Two threshold fields exist for such samples: the low and high one, respectively, due to the coarse and fine grains. Two saturation levels are found for ∥χ″, approximately proportional to the respective volume fractions of fine and coarse grains. An expression for continuously x-distributed polycrystals is worked out on the basis of the single grain scattering mechanism, which compares favorably to experimental results.

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