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Excitation and Amplification of Propagating Spin Waves by Spin Currents
Published in Sergej O. Demokritov, Spin Wave Confinement, 2017
Vladislav E. Demidov, Sergej O. Demokritov
An alternative approach to the implementation of STT devices that avoids these shortcomings utilizes pure spin currents—flows of spin not accompanied by directional transfer of electrical charge. This approach does not require the flow of electrical current through the active magnetic layer, resulting in reduced Joule heating and electromigration effects. One can also eliminate the electrical leads attached to the magnetic layer to drain the electrical current, enabling novel geometries of the STT devices. Additionally, it becomes possible to use insulating magnetic materials [27] such as yttrium iron garnet (YIG) [28]. The main advantage of this material is its exceptionally low dynamic magnetic damping. Since the expected density of the driving current necessary for the current-induced auto-oscillations is proportional to damping, YIG-based STT devices can be significantly more efficient than the traditional devices based on the transition-metal ferromagnets.
The Dynamics of Instrumentation Mechanisms
Published in S.T. Smith, D.G. Chetwynd, Foundations of Ultraprecision Mechanism Design, 2017
Stand-alone dampers, that is dissipating mechanisms, are effective for many conventional applications, but may require more relative motion than can be tolerated in our context. Magnetic damping, for example through eddy-currents, tends to fall in this category. Magnetoelastic materials (see also Section 7.1.6) provide a single material equivalent that may be better at small amplitudes. Strain results in their magnetic domains being irreversibly distorted, causing a net energy loss that provides mechanical damping. Nivco (72% Ni, 23% Cr) is of particular interest. It has a loss coefficient that increases linearly with applied stress, is significantly higher than almost all metals at low amplitude and, for the majority of engineering applications, can be considered independent of frequency, Harris and Crede, 1961.
Silicon Materials
Published in Robert Doering, Yoshio Nishi, Handbook of Semiconductor Manufacturing Technology, 2017
Figure 3.28 shows models proposed by Hoshi et al. [77] for the magnetic damping of the melt flow for VMCZ and HMCZ. In view of the model for VMCZ, the melt flow from outer to center regions of the melt (flow perpendicular to the vertical magnetic flux) are retarded. Under this condition, the forced convection induced by the crystal rotation is an effective transport for the oxygen-rich melt from the crucible bottom to the growing crystal. As the melt aspect ratio is reduced during the crystal growth, at some transition point, the forced convection would take over as the dominant transport mechanism and the incorporation level is sharply increased. The occurrence of this “transition” seems to depend on the crystal rotation used, the higher the crystal rotation, the sooner this transition occurs during the growth. It is interesting to note that the observed “transition” in incorporation level for the VMCZ growth is similar to that discussed earlier for normal CZ growth under high crystal rotation (30 rpm) with the crucible in iso-rotation mode (2 rpm) (see Figure 3.14). In both cases, the behavior is attributed to strong crystal-rotation-induced convection. In the case of HMCZ, the model of Hoshi et al. shows that the transverse magnetic flux damps the vertical melt flow near the wall, due to thermal convection and crucible rotation, resulting in retarded oxygen transport and therefore, a low level of oxygen incorporation. The forced convection induced by the crystal and crucible rotations is more effective in the transverse direction, parallel to the magnetic flux. Thus, the increased crucible rotation would help crucible dissolution and transport of the oxygen-rich melt follow flow path delineated in the model.
Design of a tuned vibration absorber for a slender hollow cylindrical structure
Published in Mechanics Based Design of Structures and Machines, 2020
Tuğrul Aksoy, Gökhan Osman Özgen, Bülent Acar
For the needed damping, use of magnetic damping mechanism is selected. Magnetic damping, also called as eddy-current damping, is a damping mechanism caused by the motion of a conductor in a magnetic field. As a result of this motion, eddy currents circulate in the conductor body, thus this current causes energy dissipation in the conductor body because of the electrical resistance of conductor. This energy dissipation results in a viscous like damping mechanism since the resistance force against the eddy currents is proportional to the relative velocity between conductor and magnetic field (Kienholtz et al. 1994). Advantages of magnetic damping over other common damping mechanisms such as viscoelastic damping and friction damping are its independence from temperature (Maly and Napolitano 1993), linear viscous characteristics (Maly and Napolitano 1993; Kienholtz et al. 1994) and convenience for the adjustment of the amount of damping added to the structure. In the literature, there are numerous studies on magnetic damping. Bae et al. (2009), Hahn et al. (1998) and Ebrahimi et al. (2008) investigated the use of eddy current damping to introduce damping directly into mechanical structures. Bae et al. (2012), Sharma et al. (2011), Sodano et al. (2005) and Kienholtz et al. (1994) specifically examined the use of magnetically damped TVAs to suppress the vibrations in different mechanical structures.