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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  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 . 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.
We analyze spin wave-based logic circuits as a possible route to building reconfigurable magnetic circuits compatible with conventional electron-based devices. A distinctive feature of the spin wave logic circuits is that a bit of information is encoded into the phase of the spin wave. It makes possible to transmit information as a magnetization signal through magnetic waveguides without the use of an electric current. By exploiting sin wave superposition, a set of logic gates such as AND, OR, and Majority gate can be realized in one circuit. We present experimental data illustrating the performance of a three-terminal micrometer scale spin wave-based logic device fabricated on a silicon platform. The device operates in the GHz frequency range and at room temperature. The output power modulation is achieved via the control of the relative phases of two input spin wave signals. The obtained data shows the possibility of using spin waves for achieving logic functionality. The scalability of the spin wave-based logic devices is defined by the wavelength of the spin wave, which depends on the magnetic material and waveguide geometry. Potentially, a multifunctional spin wave logic gate can be scaled down to 0.1μm2. Another potential advantage of the spin wave-based logic circuitry is the ability to implement logic gates with fewer elements as compared to CMOS-based circuits in achieving same functionality. The shortcomings and disadvantages of the spin wave-based devices are also discussed.
We investigate spin wave propagation and interference in conducting ferromagnetic nanostructures for potential application in spin wave based logic circuits. The novelty of this approach is that information transmission is accomplished without charge transfer. A bit of information is encoded into the phase of spin wave propagating in a nanometer thick ferromagnetic film. A set of “AND”, “NOR”, and “NOT” logic gates can be realized in one device structure by utilizing the effect of spin wave superposition. We present experimental data on spin wave transport in 100nm CoFe films at room temperature obtained by the propagation spin wave spectroscopy technique. Spin wave transport has been studied in the frequency range from 0.5 GHz to 6.0 GHz under different configurations of the external magnetic field. Both phase and amplitude of the spin wave signal are sensitive to the external magnetic field showing 60Deg/10G and 4dB/20G modulation rates, respectively. Potentially, spin wave based logic circuits may compete with traditional electron-based ones in terms of logic functionality and power consumption. The shortcomings of the spin wave based circuits are discussed.
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