from Section IV - Spin-based devices
Published online by Cambridge University Press: 05 February 2015
Introduction
A spin wave is a collective oscillation of spins in a spin lattice around the direction of magnetization. Similar to lattice waves (phonons) in solid systems, spin waves appear in magnetically ordered structures, and a quantum of a spin wave is called a “magnon.” Magnetic moments in a magnetic lattice are coupled via the exchange and dipole–dipole interaction. Any local change of magnetization (disturbance of magnetic order) results in the collective precession of spins propagating through the lattice as a wave of magnetization – a spin wave. The energy and impulse of the magnons are defined by the frequency and wave vector of the spin wave. Similar to phonons, magnons are bosons obeying Bose–Einstein statistics. Spin waves (magnons) as a physical phenomenon have attracted scientific interest for a long time [1, 2] and a variety of experimental techniques including inelastic neutron scattering, Brillouin scattering, X-ray scattering, and ferromagnetic resonance have been applied to the study of spin waves [3, 4]. Over the past two decades, a great deal of interest has been attracted to spin wave transport in artificial magnetic materials (e.g., composite structures, so-called “magnonic crystals” [5, 6]) and magnetic nanostructures [7–9]. New experimental techniques including time-domain optical and inductive techniques [7] have been developed to study the dynamics of spin wave propagation. In order to comprehend the typical characteristics of the propagating spin wave, we will refer to the results of the time-resolved measurement of propagating spin waves in a 100 nm thick NiFe film presented in [8]. In this experiment, a set of asymmetric coplanar strip (ACPS) transmission lines was fabricated on top of permalloy (Ni81Fe19) film. The strips and magnetic layer are separated by an insulating layer. One of the transmission lines was used to excite a spin wave packet in the ferromagnetic film, and the rest of the lines located 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm away from the excitation line were used for detection of the inductive voltage. When excited by the 100 ps pulse, spin waves produce an oscillating inducting voltage, which reveals the local change of magnetization under the line caused by the spin wave propagation.
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