Nonlocal damping of spin waves in a magnetic insulator induced by normal, heavy, or altermagnetic metallic overlayer: A Schwinger-Keldysh field theory approach

Abstract

Understanding spin wave (SW) damping, and how to control it to the point of being able to amplify SW-mediated signals, is one of the key requirements to bring the envisaged magnonic technologies to fruition. Even widely used magnetic insulators with low magnetization damping in their bulk, such as yttrium iron garnet, exhibit 100-fold increase in SW damping due to inevitable contact with metallic layers in magnonic circuits, as observed in very recent experiments [I. Bertelli et al., Adv. Quantum Technol. 4, 2100094 (2021)] mapping SW damping in spatially-resolved fashion. Here, we provide microscopic and rigorous understanding of wavevector-dependent SW damping using extended Landau-Lifshitz-Gilbert equation with nonlocal damping tensor, instead of conventional local scalar Gilbert damping, as derived from Schwinger-Keldysh nonequilibrium quantum field theory. In this picture, the origin of nonlocal magnetization damping and thereby induced wavevector-dependent SW damping is interaction of localized magnetic moments of magnetic insulator with conduction electrons from the examined three different types of metallic overlayers -- normal, heavy, and altermagnetic. Due to spin-split energy-momentum dispersion of conduction electrons in the latter two cases, the nonlocal damping is anisotropic in spin and space, and it can be dramatically reduced by changing the relative orientation of the two layers when compared to the usage of normal metal overlayer.

7 pages, 4 figures

References in corpus (24)

• Spin Transfer Torques
• Roadmap on Spin-Wave Computing
• Giant and tunneling magnetoresistance effects from anisotropic and valley-dependent spin-momentum interactions in antiferromagnets
• Identification of the dominant precession damping mechanism in Fe, Co, and Ni by first-principles calculations
• Spontaneous Magnon Decays
• Electronic control of the spin-wave damping in a magnetic insulator
• Nonmagnetic Ground State in RuO${}_2$ Revealed by Muon Spin Rotation
• Andreev reflection at the altermagnet-superconductor interface
• Predictable gate-field control of spin in altermagnets with spin-layer coupling
• Fragility of the magnetic order in the prototypical altermagnet RuO${}_2$
• Large-amplitude coherent spin waves exited by spin-polarized current in nanoscale spin valves
• Spin-orbit-torque magnonics
• Transverse spin diffusion in ferromagnets
• Inhomogeneous Gilbert damping from impurities and electron-electron interactions
• Magnon damping in the zigzag phase of the Kitaev-Heisenberg-$\Gamma$ model on a honeycomb lattice
• Imaging spin-wave damping underneath metals using electron spins in diamond
• Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe${}_3$
• Integration and characterization of micron-sized YIG structures with very low Gilbert damping on arbitrary substrates
• Stimulated amplification of propagating spin waves
• Spin Waves in Ferromagnetic Insulators Coupled via a Normal Metal
• Quantum many-body states and Green functions of nonequilibrium electron-magnon systems: Localized spin operators vs. their mapping to Holstein-Primakoff bosons
• Gilbert damping in metallic ferromagnets from Schwinger-Keldysh field theory: Intrinsically nonlocal and nonuniform, and made anisotropic by spin-orbit coupling
• Influence of non-local damping on magnon properties of ferromagnets
• Universal spin wave damping in magnetic Weyl semimetals

Cited by in corpus (2)

• Magnon spectrum of altermagnets beyond linear spin wave theory: Magnon-magnon interactions via time-dependent matrix product states vs. atomistic spin dynamics
• Optically induced magnetic inertia and magnons from non-Markovian extension of the Landau-Lifshitz-Gilbert equation