Physics teachers have long employed video clips to study moving objects in their classrooms and instructional labs. A number of approaches exist, both free and commercial, for tracking the coordinates of a point using video. The main characteristics of the method described in this paper are: it is simple to use; coordinates can be tracked using any standard Internet navigator; it can be used with examples available on our webserver or with a modified example in the user's own computer; the web pages with new sequences of images are easy to upload to a web server; it is possible to track and analyze any complex one- or two-dimensional motion of objects; and the code is open source. The setup is very simple, intuitive, and can easily be scaled up.
Yttrium iron garnet is widely investigated for its suitability in applications ranging from magneto-optical and microwave devices to magnonics. However, in the fewnanometer thickness range, epitaxial films exhibit a strong variability in magnetic behavior that hinders their implementation in technological devices. Here, direct visualization and spectroscopy of the atomic structure of a nominally stoichiometric thin film, exhibiting a small damping factor of 3.0 • 10 À 4 , reveals the occurrence of Y-excess octahedral antisite defects. The two-magnon strength is very small, Γ 0 � 10 À 6 Oe, indicating a very low occurrence of scattering centers. Notably, the saturation magnetization, 4πM s = 2.10 (� 0.01) kOe, is higher than the bulk value, in consistency with the suppression of magnetic moment in the minority octahedral sublattice by the observed antisite defects. Analysis of elemental concentration profiles across the substrate-film interface suggests that the Y-excess is originated from unbalanced cationic interdiffusion during the early growth stages.
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