No abstract

We have used “trapped spin wave” or edge modes of magnetic precession to probe the magnetic environment near magnetic film edges magnetized perpendicular to the edge. Micromagnetic models of dynamics in stripes reveal that the edge mode frequency-field relationship depends on whether the edge surface is vertical or tapered, while the “bulk” modes are nearly unaffected. The models show the edge-mode frequency going to zero at the edge saturation field. This critical field becomes much less distinct for applied fields misaligned from the edge normal by as little as 1°. Ferromagnetic-resonance and Brillouin light-scattering measurements of the edge modes in an array of 480-nm-wide×12-nm-thick Ni80Fe20 stripes have a lower edge saturation field than the vertical edge models, but agree well with the model of 45°-tapered edges.

Maximization of the quality factors Q of langasite (LGS) and langatate (LGT) is necessary for optimal performance of acoustic resonators of these materials in frequency-control and hightemperature sensing applications. In this report, measurements and least-squares analysis of Q À1 as a function of ultrasonic frequency and temperature of undoped LGS (100 K to 750 K) and LGT (300 K to 760 K) reveal a superposition of physical effects, including point-defect relaxations and intrinsic phonon-phonon loss. In LGS, these effects are superimposed on a large temperature-dependent background with weak frequency dependence that is interpreted as arising from a relaxation process with a distribution of activation energies. This distributed relaxation is suggested to be a result of anelastic kink migration. No evidence for a significant background of this form is found in the LGT specimen, consistent with the lower measured dislocation etch-pit density of this crystal. The analysis of the dependence of Q À1 of LGT on frequency and temperature indicates that, at near-ambient temperatures, the damping in this specimen is close to the intrinsic limit determined by phononphonon interactions. Piezoelectric=carrier relaxation, which must occur at sufficiently elevated temperatures, is found not to be a significant contribution to Q À1 , relative to defect-related contributions, in either LGS or LGT in the measured range of temperatures. V

No abstract

The advancement of imprint lithography as a method for fabricating nanostructures is impeded by a lack of effective tools for characterizing mechanical properties and geometry at the nanoscale. This paper describes progress in establishing methods for determining elastic moduli and cross sectional dimensions of imprinted nanolines from Brillouin light scattering (BLS) measurements using finite-element (FE) and Farnell-Adler models for the vibrational modes. An array of parallel nanoimprinted lines of polymethyl methacrylate (PMMA) with widths of ~65 nm and heights of ~140 nm served as a model specimen. Several acoustic modes were observed with BLS in the low-gigahertz frequency range, and the forms of the vibrational displacements were identified through correlation with calculations using measured bulk-PMMA moduli and density as input. The acoustic modes include several flexural, Rayleigh-like, and Sezawa-like modes. Fitting of Farnell-Adler calculations to the measured dispersion curves was explored as a means of extracting elastic moduli and nanoline dimensions from the data. Some of the values obtained from this inversion analysis were unrealistic, which suggests that geometric approximations in the model introduce significant systematic errors. In forward calculations, the frequencies determined with the FE method were found to more closely match experimental values, which suggests that this method may be more accurate for inversion analysis. Initial estimates of uncertainties in the FE calculations support this conclusion.