Subsidiary-absorption butterflycurves of the spin-wave-instability threshold microwave-fieldamplitude versus static field H, for an in-plane magnetized 1.1 mm X2.0 mm, 7-pm-thick yttrium iron garnet film rectangle at 9.4 6Hz, and with the linearly polarized microwave field perpendicular to the static field H and also in-plane, are found to show significant changes when H is changed from along the long edge to along the short edge of the rectangle. This effect is explained by a theory for the first-order spin-wave-instability threshold in magnetic films, which takes into acocunt the coupled standing spinwave modes across the lateral dimensions of the film. This theory is a modification of a previous theory, which considered the standing modes across the film cross section only. The theory is able to reproduce the orientation effect found experimentally and give good fits to the butterfly-curve data. In contrast with previous results, it is not necessary to introduce ad hoc spin-wave angle Oz terms into the spin-wave linewidth to obtain these fits. The theory also yields critical-mode wave numbers in the kink region which are in the 5 X 10 cm ' range, which agree with previous fine-structure and Brillouin lightscattering measurements. A key parameter in the analysis is a mode spacing parameter Acoz, which contains a factor of the form sin(20&)/K, where K is the mode wave number and 19~is the mode in-plane angle relative to H. These dependences are the key to the match with experiment. They are also general, and not limited to the thin-film geometry.
In SmB6 single crystals we observe a very anomalous ESR spectrum of Gd below 5 K. As far as we know, this is the first Gd spectrum, which cannot be explained by the electronic configuration Gd3+ 4f7. We discuss the appearance of the anomalous spectrum below 5 K by a trapped conduction electron, forming a formal divalent Gd 4f7 5d1 ground state. Above 6 K, where the conduction band of SmB6 becomes populated, we observe the usual Gd3+ Dysonian resonance as in conventional metals. The Hamiltonian of the 4f7 5d1 configuration, including a dynamic Jahn-Teller effect of the 5d electron, describes the complicated Gd spectrum reasonably well. The question, why SmB6, until now, seems to be the only host in which Gd3+ attracts a further electron, remains open.
A fine structure in the parallel pumping spin wave instability absorption has been observed. The data were obtained at 9.4 GHz on a narrow linewidth in-plane magnetized yttrium iron garnet film with a magnetic layer thickness of 15.9 pm. The standard butterfly curve of the spin wave instability threshold microwave field amplitude h Ctit versus external static magnetic field H,, was constructed from h,si, determinations obtained by sweeping the static field at different microwave power levels and measuring the change in microwave loss. For values of Hex* below the minimum, hCtit position, the loss versus Hext profiles showed a characteristic fine structure previously observed only in spheres. The fine structure spacing was on the order of 5 Oe and the square of the spacing decreased linearly with increasing static field. These fine structure results are in accord with predictions from theory for critical modes at one-half the pump frequency, with the critical mode wave vectors aligned perpendicular to the film plane, and with the wave numbers for these modes quantized as standing spin wave modes for a thin film. Analysis of the fine structure data gives a spin wave exchange stiffness parameter Dfr= (6.010.9) x lo-' Oe cm2, which agrees within experimental error with the value D= (5.4AO.2) x lo-' Oe cm-' obtained from Brillouin light scattering measurements on YIG spheres. The standing wave critical modes are explained in terms of cooperative volume dipole-dipole and shape demagnetizing induced ellipticity for the modes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.