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We have studied the magnetization reversal processes in polycrystalline CoPt magneto-optic recording alloys with perpendicular magnetic anisotropy. Thin films of composition with total thicknesses in the range 5 nm to 30 nm were investigated with Kerr contrast imaging. Depending on the film deposition parameters we find domain wall motion or domain nucleation dominated processes. Numerical simulations of the magnetization reversal processes were carried out within a two-dimensional array model of interacting mesoscopic single domain particles. Including dipolar fields and domain wall contributions, we find that the demagnetizing fields dominate the reversal mechanisms and strongly affect the shape of the hysteresis loops. Additional microstructural analysis reveals that the typical grain sizes of the (111) textured polycrystalline alloy films are of the order of about 20 nm which coincides with the typical cell size representing a single domain particle in the micromagnetic numerical simulations.

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An improved thermal model of bulk acoustic wave quartz resonators, which is different from the ‘‘infinite plate’’ model, is proposed. It takes into account the actual boundary conditions and energy trapping. Inside the resonator, three parts are distinguished: an internal source part, a transfer part, and an exchange part. The thermal steady state is studied, the model validity limits being pointed out. Three typical parameters are proposed to specify the resonator thermal state. Principal results for coated and electrodeless quartz resonators are given. Especially, the value of thermal radial gradient is computed and its share in the oscillator’s frequency shifts due to transient thermal phenomena is pointed out.