Magnonics: spin waves connecting charges, spins and photons

Abstract

Spin waves (SW) are the excitation of the spin system in a ferromagnetic condensed matter body. They are collective excitations of the electron system and, from a quasiclassical point of view, can be understood as a coherent precession of the electrons' spins. Analogous to photons, they are also referred to as magnons indicating their quasi-particle character. The collective nature of SWs is established by the shortrange exchange interaction as well as the non-local magnetic dipolar interaction, resulting in coherence of SWs from mesoscopic to even macroscopic length scales. As one consequence of this collective interaction, SWs are "charge current free" and, therefore, less subject to dissipation caused by scattering with impurities on the atomic level. This is a clear advantage over diffusive transport in spintronics that not only uses the charge of an electron but also its spin degree of freedom. Any (spin) current naturally involves motion and, thus, scattering of electrons leading to excessive heating as well as losses. This renders SWs a promising alternative to electric (spin) currents for the transport of spin information -one of the grand challenges of condensed matter physics.The possibilities of SWs being a new means of information carriers stimulated the emerging research eield called "magnonics". Its name -inspired by the terms "spintronics" and "photonics" -indicates the main driving force behind magnonics: exploiting SWs for information processing to supersede electronics. For frequencies ranging from gigahertz to terahertz, the SW wavelengths can be as small as only a few nanometers, orders of magnitude smaller compared to electromagnetic waves. In addition, their transport properties exhibit a strong dependence on the magnetization coneiguration that can be non-volatile and still reconeigurable on a sub-nanosecond timescale.The eield of modern magnonics is very wide and covers a variety of emerging physical phenomena. Some of the magnonics research directions are brieely summarized in Fig. 1. We present the directions that are already well established as well as the directions that are just at their initial state of their development but show large potential. In addition, one can see in the eigure that the material science,

Ultralow Magnetic Damping in Co2Mn -Based Heusler Compounds: Promising Materials for Spintronics

“…For continued progress, magnetic materials with specific and dedicated properties are needed, such as a high Curie temperature and an appropriate magnetic anisotropy for thermal stability [9], a high spin polarization at the Fermi energy to obtain fully spin-polarized currents, and a small magnetic damping to easily generate magnetization precession. All of these properties are desirable for STT, SOT and AOS based devices [9] but also in spin-wave-based devices, an emergent research field called magnonics [10].…”

Co25Fe75Thin Films with Ultralow Total Damping of Ferromagnetic Resonance

“…Emerging applications in magnonics [1], spin-orbitronics [2] as well as fundamental studies in linear and non-linear magnetization dynamics [3] rely on materials that exhibit low values of the magnetic damping parameter. Insulating ferromagnets and ferrites -lacking a significant electronmagnon relaxation channel -have historically exhibited the lowest magnetic dissipation at room temperature.…”

“…Indeed, two recent studies reported the growth of Co25Fe75 on MgO and MAO resulting in values of the damping parameters around 0.001 [11,12]. Removing the constraint of epitaxial growth on single crystalline substrates while maintaining low magnetic damping and high film uniformity may enable integration of this material in a wide range of spintronic and magnonic devices [1,2].…”

Anomalous Behaviors of Spin Waves Studied by Inelastic Light Scattering

“…Magnonics, a young and evolving field, has received extensive research interests in the modern magnetism research community [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Similar to spintronics, which deals with electron spin, magnonics utilizes magnon (the quanta of spin wave) to carry and process information.…”