[en] Using Brillouin scattering, we have determined the complete set of elastic constants of the technologically important β-Si₃N₄. Availability of single crystals has allowed us to measure all five independent c_ij, which (in units of GPa) are: c₁₁=433(3), c₃₃=574(3), c₁₃=127(5), c₄₄=108(2), c₆₆=119(4), and c₁₂=c₁₁-2c₆₆=195(8), giving a bulk modulus of 259. Our values are compared with existing calculations and c_ij determined from nano-indentation results combined with empirical relations and trends in related materials. (c) 2000 American Institute of Physics

[en] We have observed the field dependence and enhancement of the intensity of polarized elastic light scattering, from ultrathin magnetic films with perpendicular magnetic anisotropy (PMA). High-resolution Brillouin spectroscopy elucidates that this enhancement reaches its maximum at a critical field (H_crit) where the magnetization starts to incline toward out-of-plane due to the strong PMA. We attribute this new effect to the microscopic instability due to random fluctuations of the magnetization near H_crit, since this elastic scattering has no frequency shift from the excitation light and thus the correlation of each spin decays monotonically. The enhancement factor depends on the PMA strength as well as the film thickness, and we obtain an enhancement as large as a factor of 20 at room temperature with a low external field of 0.18 kOe. (c) 2000 American Institute of Physics

[en] We have observed spin-wave Brillouin light scattering from ultrathin Co/Au/Cu(111) films with Co thicknesses t_Co down to 1 monolayer (ML) and with a 1-ML Au interlayer. The detection of a well-defined spin-wave spectrum and the field dependence of its frequency show directly long-range collective and ferromagnetic ordering in these films at room temperature. From the field dependence of the spin-wave frequency, we derive uniaxial perpendicular magnetic anisotropy constants as a function of t_Co with various overlayer materials, including Cu, Pd, and Au. With a Cu overlayer, we observe that the first-order perpendicular anisotropy K_u⁽¹⁾ obeys well a linear relation between K_u⁽¹⁾t_Co and t_Co for t_Co≥1.5 ML, which indicates a constant contribution of the interface anisotropy of 0.16 mJ/m2 in addition to the volume anisotropy of 0.73 MJ/m3. With an Au or a Pd overlayer, we find that both the interface and volume anisotropies are significantly larger than those with the Cu overlayer. We quantify magnetic inhomogeneities from the field dependence of the spectrum width. With the Au or Pd overlayer, K_u⁽¹⁾ shows a steep decrease with decreasing t_Co for t_Co<3.0 ML, which agrees well with a significant increase in the structure-related magnetic inhomogeneity. We show directly that long-ranged ferromagnetic ordering exists, with the perpendicular anisotropy, in our quasimonatomic Co films thinner than 1.5 ML. K_u⁽¹⁾ for each overlayer tends to be zero at 1 ML of Co, accompanied by heavy damping of the spin wave. In addition, we find the second-order perpendicular anisotropy is still maintained with a comparable value to K_u⁽¹⁾ in such quasimonatomic Co films, indicating significant deformation of the uniaxial anisotropy. (c) 2000 The American Physical Society

[en] A spin-wave Brillouin scattering study of a CoPt-SiO₂ granular magnetic recording medium was made. This film contains ferromagnetic CoPt particles in a SiO₂ matrix, and has an extremely low medium noise property due to little exchange coupling between magnetic grains. Spin waves of both the propagating surface mode and standing wave mode were found to be excited in granular magnetic films with various microstructures. A possible origin of the spin wave is a magnetostatic coupling between regularly ordered CoPt grains, as reported for artificially patterned magnetic thin films. This result shows two promising features of the CoPt-SiO₂ granular film for high density recording medium: It is an ordered media obtained in a self-organizing manner, and it is less influenced by the thermal fluctuation effect, which is a serious problem for current high density magnetic recording. (c) 2000 American Institute of Physics