Spin-wave Packets Research Articles

Spin waves interference from rising and falling edges of electrical pulses

The authors have investigated the effect of the electrical pulse width of input excitations on the generated spin waves in a NiFe strip using pulse inductive time domain measurements. The authors have shown that the spin waves resulting from the rising- and the falling-edges of input excitation pulses interfere either constructively or destructively and have provided conditions for obtaining spin wave packets with maximum intensity at different bias conditions.

Variable damping and coherence in a high-density magnon gas

We report on the fast relaxation behavior of a high-density magnon gas created by a parametric amplification process. The magnon gas is probed using the technique of spin-wave packet recovery by parallel parametric pumping. Experimental results show a damping behavior which is in disagreement with both the standard model of exponential decay and with earlier observations of non-linear damping. In particular, the inherent magnon damping is found to depend upon the presence of the parametric pumping field. A phenomenological model which accounts for the dephasing of the earlier injected magnons is in good agreement with the experimental data.

Optimum design consideration for interferometric spin wave logic operations

In the present study, the operational modes and the structural design are optimized to realize potential performance in the interferometric spin wave logic circuits. Successive functional operations, such as generation, propagation, and inductive detection of spin wave packets are numerically studied by using micromagnetic simulations. The logic input is coded with the phase of pulsed microwave currents applied through the generators. Among the various kinds of the investigated spin wave (SW) modes, the backward volume mode exhibits superior performance. Various structural and operational parameters, including the pulsed microwave frequency and the film thickness of the magnetic strip, were optimized by taking the inductive output voltage (Vout) as a quantitative criterion. The several orders of difference obtained in the Vout for the different logic inputs demonstrates the successful exclusive-not-OR operation.

Nonreciprocal emission of spin-wave packet in FeNi film

We report a time-resolved propagating spin wave spectroscopy for Fe19Ni81 film. We show that the amplitude of the spin-wave packet depends on the direction of magnetization and that its phase can be controlled by the polarity of pulsed magnetic field for the excitation. The nonreciprocal emission of spin-wave packet can be utilized for the binary spin-wave input into the spin-wave logic circuit.

Formation of Random Dark Envelope Solitons from Incoherent Waves

This Letter reports experimental results on random temporal dark solitons. One excites an incoherent large-amplitude propagating spin-wave packet in a ferromagnetic film strip with a repulsive, instantaneous nonlinearity. One then observes the random formation of dark solitons from this wave packet. The solitons appear randomly in time and in position relative to the entire wave packet. They can be gray or black. In spite of the randomness of the initial wave packets and the random formation processes, the solitons show signatures that are found for conventional coherent dark solitons.

Formation of envelope solitons of spin-wave packets propagating in thin-film magnon crystals

The formation of light envelope solitons has been experimentally observed under the pulsed excitation and propagation of radio-frequency spin-wave packets in a magnon crystal, a periodic magnetic film structure. The magnon crystal has been fabricated from a thin single-crystal yttrium iron garnet (YIG) film. The envelope solitons have been excited at frequencies corresponding to the edges of the Bragg-resonance-induced band gaps of the spin-wave spectrum of the magnon crystal. A theoretical explanation of the observed phenomenon has been proposed with the use of the numerical simulation of the formation of solitons based on the nonlinear Schrodinger equation.

Quantum Transport through a Tonks-Girardeau Gas

We investigate the propagation of spin impurity atoms through a strongly interacting one-dimensional Bose gas. The initially well localized impurities are accelerated by a constant force, very much analogous to electrons subject to a bias voltage, and propagate as a one-dimensional impurity spin wave packet. We follow the motion of the impurities in situ and characterize the interaction induced dynamics. We observe a very complex nonequilibrium dynamics, including the emergence of large density fluctuations in the remaining Bose gas, and multiple scattering events leading to dissipation of the impurity's motion.

Generation of spin-wave pulse trains by current-controlled magnetic mirrors

The evolution of a packet of long-wavelength, dipole-dominated spin waves trapped between two direct current-carrying wires placed on the surface of a ferrite film is observed by Brillouin light scattering. The wires act as semitransparent mirrors confining the packet. Because the spin-wave energy partially passes through these mirrors, trains of spin-wave packets are generated outside the trap. A numerical model is presented and applied to the case when the current in the wires is dynamically controlled. The dynamic control of the mirror reflectivity provides new functionalities interesting for the field of spin-wave logic like that of a spin-wave memory cell.

Emission of noise-like spin wave packets in the presence of three-magnon decay processes and the kinetic instability of waves in a ferromagnetic film

The features of spin wave emission from a ferromagnetic film in the direction of the propagation of a surface magnetostatic wave have been experimentally investigated at various input signal powers. Radiation in the form of two noise-like spin wave packets has been detected near the frequency corresponding to half the pump frequency. This radiation is caused by three-magnon processes of the decay of a surface magnetostatic wave and by the kinetic instability of spin waves.

Notes on <I>Hymenoscyphus</I> — 3: On the nomenclature of <I>Hymenoscyphus subcarneus</I> (<I>Ascomycota, Helotiales</I>)

Spin waves—the elementary excitations of magnetic materials—are prime candidate signal carriers for low-dissipation information processing. Being able to image coherent spin-wave transport is crucial for developing interference-based spin-wave devices. We introduce magnetic resonance imaging of the microwave magnetic stray fields that are generated by spin waves as a new approach for imaging coherent spin-wave transport. We realize this approach using a dense layer of electronic sensor spins in a diamond chip, which combines the ability to detect small magnetic fields with a sensitivity to their polarization. Focusing on a thin-film magnetic insulator, we quantify spin-wave amplitudes, visualize spin-wave dispersion and interference, and demonstrate time-domain measurements of spin-wave packets. We theoretically explain the observed anisotropic spin-wave patterns in terms of chiral spin-wave excitation and stray-field coupling to the sensor spins. Our results pave the way for probing spin waves in atomically thin magnets, even when embedded between opaque materials.

Space–time evolution of spin-wave packets

Using the transfer matrix method and the multi-channel scattering approach, we solve analytically the Schrödinger equation for spin 12 electrons moving through a homogeneous semiconductor wave guide subject to an external magnetic field, acting on alternating stripes. We study the space–time evolution of Gaussian spin-wave packets inside and outside of the homogeneous magnetic superlattices (MSL) for different tilting angles. We discuss interfering processes of spin-wave packets, defined in the band gap and in the resonant energy regions of homogeneous MSL based on an InSb semiconductor. We show also that the time spent inside the MSL is in good agreement with the phase time predictions.

Formation of Guided Spin-Wave Bullets in Ferrimagnetic Film Stripes

The formation of quasi-2D nonlinear spin-wave eigenmodes in longitudinally magnetized stripes of a ferrimagnetic film, the so-called guided spin-wave bullets, was experimentally observed by using time- and space-resolved Brillouin light scattering spectroscopy and confirmed by numerical simulation. They represent stable spin-wave packets propagating along a waveguide structure, for which both transversal instability and interaction with the side edges of the waveguide are important. The experiments and the numerical simulation of the evolution of the spin-wave excitations show that the shape of the formed packets and their behavior are strongly influenced by the confinement conditions. The discovery of these modes demonstrates the existence of quasistable nonlinear solutions in the transition regime between one-dimensional and two-dimensional wave packet propagation.

Observation of the propagation and interference of spin waves in ferromagnetic thin films

We have observed the propagation of spin waves and spin-wave packets in 20-nm-thick Permalloy films upon microwave excitation by means of time-resolved scanning Kerr microscopy. Spin waves can be detected up to $80\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{m}$ away from the driving coplanar strip line. In doing so, we were able to directly determine the phase velocities, dispersion relations and group velocities for different geometries of an externally applied in-plane magnetic field. In addition, we report on the direct optical observation of spin-wave interference with lateral and time (phase) resolution.

Parametrically Stimulated Recovery of a Microwave Signal Stored in Standing Spin-Wave Modes of a Magnetic Film

We demonstrate that a microwave signal carried by a packet of dipolar spin waves propagating in a tangentially magnetized magnetic film can be stored in the form of standing dipole-exchange spin-wave modes of the film and can be recovered by means of a double-frequency parametric pumping mechanism. This mechanism is based on the parametric amplification of the standing (thickness) modes of the film by external pumping. The time of recovery, duration, and power of the recovered pulse signal are controlled by the power of the pumping signal.

Resonant Tunneling of Spin-Wave Packets via Quantized States in Potential Wells

We have studied the tunneling of spin-wave pulses through a system of two closely situated potential barriers. The barriers represent two areas of inhomogeneity of the static magnetic field, where the existence of spin waves is forbidden. We show that for certain values of the spin-wave frequency corresponding to the quantized spin-wave states existing in the well formed between the barriers, the tunneling has a resonant character. As a result, transmission of spin-wave packets through the double-barrier structure is much more efficient than the sequent tunneling through two single barriers.

Interaction between large and small signals in a resonant transmission line based on magnetostatic waves

The influence of a large signal on the characteristics of a small signal near the frequency of the former is experimentally studied for the case of their simultaneous propagation through a resonant transmission line based on backward volume magnetostatic waves. The effects observed are caused by the excitation of spin waves in a ferromagnetic film at different large-signal frequencies and by the back influence of excited spin-wave packets on the amplitude and phase characteristics of the small signal.

Connecting the timescales in picosecond remagnetization experiments

In femtosecond demagnetization experiments, one gains access to the elementary relaxation mechanisms of a magnetically ordered spin system on a time scale of $100\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$. Following these experiments, we report a combined micromagnetic and experimental study that connects the different regimes known from all-optical pump-probe experiments by employing a simple micromagnetic model. We identify spin-wave packets on the nanometer scale that contribute to the remagnetization process on the intermediate time scale between single-spin relaxation and collective precession.

Phase-sensitive Brillouin light scattering spectroscopy from spin-wave packets

The authors report on the implementation of phase sensitivity into Brillouin light scattering spectroscopy from propagating spin-wave packets. In order to access phase information, interference between the light inelastically scattered by the spin-wave and a frequency shifted coherent reference beam is used. This approach allows for access to quantities such as the space- and time-resolved phase profile and the wave front of spin-wave packets and beams. The authors apply the developed method to investigations of the phase profiles of linear and nonlinear (soliton) spin-wave pulses. In particular, the constant phase profile characteristics for an envelope spin-wave soliton are demonstrated.

Interaction of microwave signals in a resonance transmission line based on magnetostatic waves

Interaction between two (small and large) regular microwave signals that simultaneously pass through a resonance transmission line based on backward volume magnetostatic waves is studied experimentally in different frequency ranges. It is found that the amplitude-frequency response of the small signal near the frequency of the large one depends on the frequency of the latter; namely, the amplitude of the small signal is affected by spin-wave packets parametrically excited by magnetostatic and electromagnetic pumps.

Random Generation of Coherent Solitary Waves from Incoherent Waves

The random generation of coherent solitary waves from incoherent waves in a medium with an instantaneous nonlinearity has been observed. One excites a propagating incoherent spin wave packet in a magnetic film strip and observes the random appearance of solitary wave pulses. These pulses are as coherent as traditional solitary waves, but with random timing and a random peak amplitude.