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Magnetic Insulator-Based Spintronics
Published in Xiaobin Wang, Krzysztof Iniewski, Metallic Spintronic Devices, 2017
It should be noted that thanks to the absence of Fe2+ ions, magnetic garnets generally have slower ferromagnetic relaxation than other ferrimagnetic materials.7 Moreover, in the family of magnetic garnets, YIG and substituted-YIG have the lowest relaxation rates. Indeed, YIG materials have a lower relaxation rate than any other magnetic materials, with an intrinsic damping constant α of about 3 × 10–5 only. Because of this extremely small damping, YIG materials have found rather broad current and potential applications in microwave devices.8–10 YIG sphere-based oscillators and filters, for example, are core devices in many microwave generators and analyzers.
Quantization of magnetoelectric fields
Published in Journal of Modern Optics, 2019
When analysing the scattering of EM waves by MDM disks in microwave waveguides and energy quantization of the field in a microwave cavity, it is relevant also to dwell on some basic problems of magnon-photon interaction and bound states in the microwave continuum. We are witnesses that long-standing research in coupling between electrodynamics and magnetization dynamics noticeably reappear in recent studies of magnon-photon interaction (88–93). In a structure of a microwave cavity with a YIG sphere inside, the avoided crossing in the microwave reflection spectra verifies the strong coupling between the microwave photon and the magnon (88). In these studies, the Zeeman energy is defined by a coherent state of the macrospin/photon system when a magnetic dipole is in its antiparallel orientation to the cavity magnetic field. It is worth noting however, that for our case of MDMs on a small ferrite disk, characterizing by non-uniform magnetization dynamics, the above model of coherent states of the macrospin/photon system in a ferrite sphere, is not applicable.
Magnetic dipolar modes in magnon-polariton condensates
Published in Journal of Modern Optics, 2021
In microwaves, we are witnesses that long-standing research in coupling between electrodynamics and magnetization dynamics noticeably reappear in recent studies of strong magnon-photon interaction [15–19]. In a small ferromagnetic particle, the exchange interaction can lead to the fact that a very large number of spins to lock together into one macrospin with a corresponding increase in oscillator strength. This results in strong enhancement of spin-photon coupling. In a structure of a microwave cavity with a yttrium iron garnet (YIG) sphere inside, the avoided crossing in the microwave reflection spectra verifies strong coupling between the microwave photon and the macrospin magnon. In these studies, the Zeeman energy is defined by a coherent state of the macrospin-photon system when a magnetic dipole is in its antiparallel orientation to the cavity magnetic field. Along with the analysis of the strong coupling of the cavity electromagnetic modes with the fundamental Kittel modes, coupling with non-uniform modes – the Walker or magnetostatic modes – in a YIG sphere was considered. Based on experimental studies of the effects of cavity quantum electrodynamics with ferromagnetic magnons in a small YIG sphere at both cryogenic and room temperatures, authors in Ref. [20] concluded that the magnetostatic modes are unobservable at room temperature. Nevertheless, in the room-temperature microwave experiments in Ref. [21,22], identification of the Walker modes in the sphere was made successfully based an effect of overlapping between the cavity and spin waves due to relative symmetries of the fields. It should be noted, however, that the experimentally observed effects of strong magnon-photon interaction discussed above cannot be properly described in terms of a macrospin-photon coupling process. In a view of these aspects, the theory based on solving coupled Maxwell and Landau-Lifshitz-Gilbert equations without making the conventional magnetostatic approximation have been suggested [23,24]. Currently, the studies of strong magnon-photon interaction are integrated in a new field of research called cavity spintronics (or spin cavitronics) [25,26].