Spin Wave Resonance Research Articles

Magnetic and Ferromagnetic Resonance Studies in Amorphous Co–Zr Films

The magnetic properties of amorphous Co[Formula: see text]Zrx films prepared by co-evaporation have been studied by means of vibrating sample magnetometry and ferromagnetic resonance. The temperature dependence of spontaneous magnetization [Formula: see text] in the low temperature range can be described using Bloch’s law. In addition, the spin wave stiffness constant, the distance between nearest magnetic atoms and the exchange interaction between cobalt and its nearest neighbors were calculated from the experimental results for [Formula: see text]. Spin-wave resonance modes were obtained and the change of the resonant field as a function of the mode number [Formula: see text] obeys the so-called [Formula: see text] law perpendicular to the film plane at 300[Formula: see text]K.

Probing edge condition of nanoscale CoFeB/MgO magnetic tunnel junctions by spin-wave resonance

We investigate spin-wave resonance in nanoscale CoFeB/MgO magnetic tunnel junctions (MTJs) with a perpendicular easy axis and various free-layer sizes. Two types of MTJs are fabricated by different process conditions, and the spin-wave resonance is measured with homodyne-detected ferromagnetic resonance. We focus on the distance between resonance frequencies of the uniform and spin-wave modes as a function of the free-layer size in order to examine the effect of the edge state of MTJs. A marked difference is observed between the two types of MTJs, and the result is consistently reproduced by a model assuming free- or fixed-edge boundary conditions with or without reduced magnetic properties near the pattern edge for each MTJ. The obtained results indicate that the edge state of nanoscale MTJs is crucially affected by the process condition, and spin-wave resonance can serve as a sensitive probe for the edge condition.

Non-reciprocal Pumping of Surface Acoustic Waves by Spin Wave Resonance

We predict that surface acoustic waves are generated preferentially in one direction in a heterostructure of a thin magnetic film on a non-magnetic substrate. The non-reciprocity arises from magnet...

Highly nonlinear frequency-dependent spin-wave resonance excited via spin-vorticity coupling

A nonuniform vorticity of lattice deformation in a surface acoustic wave (SAW) can generate a spin current (SC) in nonmagnetic metals via spin-vorticity coupling (SVC). We demonstrated a strong enhancement of SVC-derived SC generated in Cu and Pt films with increasing the frequency of the SAW by observing the spin-wave resonance (SWR) in an adjacent NiFe film. The comparative amplitudes and high-order frequency variations of SWR in NiFe/Cu and NiFe/Pt bilayers imply that the amplitude of the SC generated via SVC in a SAW is robust against the strength of spin-orbit interaction in nonmagnetic metals.

Spin Wave Resonance in the [(Co0.88Fe0.12)/Cu]N Synthetic Antiferromagnet

The [(Co0.88Fe0.12)/Cu]N synthetic antiferromagnet has been investigated by the spin wave resonance method over the entire range of angles of an external dc magnetic field to the film surface normal. The investigations have shown that the superlattice under study consists of two exchange-coupled magnetic subsystems, each manifested in the recorded spectra as a series of spin-wave modes. The dependence of the linear region of propagation of a standing spin-wave mode on the sample orientation in an external magnetic field has been established.

Magnetic anisotropy and exchange paths for octahedrally and tetrahedrally coordinated Mn2+ ions in the honeycomb multiferroic Mn2Mo3O8

We investigated the static and dynamic magnetic properties of the polar ferrimagnet Mn$_2$Mo$_3$O$_8$ in three magnetically ordered phases via magnetization, magnetic torque, and THz absorption spectroscopy measurements. The observed magnetic field dependence of the spin-wave resonances, including Brillouin zone-center and zone-boundary excitations, magnetization, and torque, are well described by an extended two-sublattice antiferromagnetic classical mean-field model. In this orbitally quenched system, the competing weak easy-plane and easy-axis single-ion anisotropies of the two crystallographic sites are determined from the model and assigned to the tetra- and octahedral sites, respectively, by ab initio calculations.

Spin-Wave Resonance in One-Dimensional Magnonic Crystals by an Example of Multilayer Co–P Films

Layered magnetic films of Co–P alloy, which are sets of laminates with certain atomic and chemical structures, have been investigated by spin-wave resonance. Coatings of two types were synthesized: a magnonic crystal (amorphous Co(P)/fcc Co(P))N and gradient Co(P) films. They exhibit two different modifications of the spin-wave resonance (SWR) spectrum. In the first case, the SWR spectrum is described as Hn(n) ~ n2 with a modification caused by the formation of the first stop band of the magnonic crystal. In the second case, the dependence of resonance fields Hn of the spin-wave modes on mode number n has the form of Hn(n) ~ n2/3. Thermal annealing leads to crystallization (amorphous alloy → fcc) and causes transformation of the layered films to the films of single-phase Co–P alloys, which is accompanied by a change in the shapes of the SWR spectra and occurrence of a “exchange kink” spectral modification.

Возбуждение спин-волнового резонанса в тонких магнитных пленках в отсутствие поверхностной анизотропии.

Возбуждение спин-волнового резонанса в тонких магнитных пленках в отсутствие поверхностной анизотропии.

Spin-torque oscillation in a magnetic insulator probed by a single-spin sensor

Coherent, self-sustained oscillation of magnetization in spin-torque oscillators (STOs) is a promising source for on-chip, nanoscale generation of microwave magnetic fields. Such fields could be used for local excitation of spin-wave resonances, control of spin qubits, and studies of paramagnetic resonance. However, local characterization of fields emitted by an STO has remained an outstanding challenge. Here, we use the spin of a single nitrogen-vacancy (NV) defect in diamond to probe the magnetic fields generated by an STO in a microbar of ferromagnetic insulator yttrium-iron-garnet (YIG). The combined spectral resolution and sensitivity of the NV sensor allows us to resolve multiple spin-wave modes and characterize their damping. When damping is decreased sufficiently via spin injection, the modes auto-oscillate, as indicated by a strongly reduced linewidth, a diverging magnetic power spectral density, and synchronization of the STO frequency to an external microwave source. These results open the way for quantitative, nanoscale mapping of the microwave signals generated by STOs, as well as harnessing STOs as local probes of mesoscopic spin systems.

Microwave Giant Magnetoresistance and Ferromagnetic and Spin-Wave Resonances in (CoFe)/Cu Nanostructures

The microwave phenomena that occur in magnetic multilayer (CoFe)/Cu nanostructures, which have a giant magnetoresistance, are studied. The transmission of waves through a nanostructure is used to investigate the microwave giant magnetoresistance effect. The changes in the transmission coefficient at frequencies of 29–38 GHz are found to exceed the relative magnetoresistance, which distinguishes the system under study from the nanostructures studied earlier. Ferromagnetic and spin-wave resonances are used to study the angular dependences of the microwave absorption spectra of a multilayer (CoFe/Cu)n nanostructure. The following parameters are determined: the critical angle that determines the boundaries of the ranges of excitation of uniform and nonuniform spin modes, the type of boundary conditions describing the pinning of spins on the outer nanostructure surfaces, and the surface anisotropy and exchange interaction constants.

Tunable Magnon-Magnon Coupling Mediated by Dynamic Dipolar Interaction in Synthetic Antiferromagnets.

We report an experimental observation of magnon-magnon coupling in interlayer exchange coupled synthetic antiferromagnets of FeCoB/Ru/FeCoB layers. An anticrossing gap of spin-wave resonance between acoustic and optic modes appears when the external magnetic field points to the direction tilted from the spin-wave propagation. The magnitude of the gap (i.e., coupling strength) can be controlled by changing the direction of the in-plane magnetic field and also enhanced by increasing the wave number of excited spin waves. We find that the coupling strength under the specified conditions is larger than the dissipation rates of both the resonance modes, indicating that a strong coupling regime is satisfied. A theoretical analysis based on the Landau-Lifshitz equation shows quantitative agreement with the experiments and indicates that the anticrossing gap appears when the exchange symmetry of two magnetizations is broken by the spin-wave excitation.

Single-ion anisotropy driven splitting of spin wave resonances in BiFeO3 at low temperature**This paper is dedicated to Dr C S Sundar, Senior Professor, HBNI and J C Bose Fellow.

The spin wave resonances of BiFeO3 ceramics have been followed at low temperature through far-infrared reflectance measurements. Following the scheme of Fishman et al (2015 Phys. Rev. B 92 094422) we have been able to assign all the spin wave modes observed. A complete lifting of the degeneracies of all these modes is seen at 250 K concomitant with the increase in single-ion anisotropy. For the first time, all the spin wave modes have been observed in the infrared spectra of BiFeO3. Correlated changes in the strength and frequencies of spin wave excitations with the reported magnetic transitions at low temperature are observed. A simultaneous increase in anharmonicity of the magnetic cycloid and single-ion anisotropy with decreasing temperature results in a partial suppression of the spin wave excitations. An increase in the magnetoelectric coupling is also observed below 150 K.

Observation of Gyromagnetic Spin Wave Resonance in NiFe Films.

This Letter demonstrates spin wave resonance (SWR) owing to the gyromagnetic effect by propagating a Rayleigh-type surface acoustic wave (R-SAW) through ferromagnetic thin films. The SWR amplitude in a NiFe film shows a higher-order frequency variation than in a magnetoelastic Ni film. This frequency dependence is well understood in terms of the presence of a gyromagnetic field attributable to the local lattice rotation in the R-SAW. From the frequency dependence of the SWR amplitude, the gyromagnetic SWR could be separated from another SWR caused by a magnetoelastic effect of the ferromagnet.

Hybrid nanophotonic-nanomagnonic SiC-YiG quantum sensor: II/dark spins quantum sensing with V2 spins and fiber based OP-PELDOR/ODMR

First experiments like optically detected (OD) electron paramagnetic resonance (ODMR), photoluminescence detected RABI oscillations, and optical pumping (OP) assisted pulsed EPR measurements of T2 and T1 of V2 spins in bulk SiC, which were previously demonstrated on various home build EPR spectrometers with free space optics, are here all demonstrated for the first time using a commercial X band pulsed EPR spectrometer combined with a single optical fiber and a standard external photoluminescence setup. Quantum sensing of bulk dark spins dipolar coupled to V2 spins in SiC is also demonstrated here for the first time using single fiber based OP assisted pulsed electron electron double resonance spectroscopy (PELDOR). A spin wave resonance study of model permalloy nanostripes is also presented allowing to check the ferromagnetic nanostripes design. These experiments are first key steps towards the fiber-based integration of the recently proposed SiC-YiG quantum sensor device [J. Tribollet, Eur. Phys. J. Appl. Phys.90, 20102 (2020)], to a commercially available and worldwide used pulsed EPR spectrometer, with important applications expected in structural biology, surface chemistry, and quantum computing.

Effect of interface magnetization depinning on the frequency shift of ferromagnetic and spin wave resonance in YIG/GGG films**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674187 and 51871127) and Technology on Electronic Test & Measurement Laboratory (Grant No. 6142001180103).

Nowadays the yttrium iron garnet (Y3Fe5O12, YIG) films are widely used in the microwave and spin wave devices due to their low damping constant and long propagation distance for spin waves. However, the performances, especially the frequency stability, are seriously affected by the relaxation of the interface magnetic moments. In this study, the effect of out-of-plane magnetization depinning on the resonance frequency shift (Δfr) was investigated for 3-μm YIG films grown on Gd3Ga5O12 (GGG) (111) substrates by liquid-phase epitaxy. It is revealed that the ferromagnetic resonance (FMR) and spin wave propagation exhibit a very slow relaxation with relaxation time τ even longer than one hour under an out-of-plane external magnetic bias field. The Δfr span of 15.15–24.70 MHz is observed in out-of-plane FMR and forward volume spin waves. Moreover, the Δfr and τ depend on the magnetic field. The Δfr can be attributed to that the magnetic moments break away from the pinning layer at the YIG/GGG interface. The thickness of the pinning layer is estimated to be about 9.48 nm to 15.46 nm according to the frequency shifting. These results indicate that Δfr caused by the pinning layer should be addressed in the design of microwave and spin wave devices, especially in the transverse magnetic components.

Spin Wave Resonance Frequency in Ferromagnetic Homogeneous Bilayers with Next Nearest Neighbor Interaction

The effects of next nearest neighbor interaction, interface coupling, surface anisotropy, film thickness and symmetry on spin wave resonance (SWR) frequency in the ferromagnetic homogeneous bilayer...

Spin-wave resonance in gradient ferromagnets with concave and convex variations of magnetic parameters

The theory of spin-wave resonance in gradient ferromagnetic films with magnetic parameters varying in space described by both concave and convex quadratic functions is developed. Gradient structures such as a potential well, a potential barrier, and a monotonic change in potential between the film surfaces for both quadratic functions are considered. The waveforms of oscillations mn(z), the laws of the dependence of discrete frequencies ωn, and relative susceptibilities χn/χ10 of spin-wave resonances on the resonance number n are studied. It is shown that the law ωn∝n for n<nc, where nc is the resonance level near the upper edge of the gradient inhomogeneity, which is well known for a parabolic potential well, is also valid for the potential barrier and for the monotonic change in potential, if these structures are formed by a concave quadratic function. It is shown that the law ωn∝(n−1/2)1/2, which we numerically derived and approximated by the analytical formula, is valid for all three structures formed by a convex quadratic function. It is shown that the magnetic susceptibility χn of spin-wave resonances for n<nc is much greater than the susceptibility of resonances in a uniform film. An experimental study of both laws ωn(n) and χn(n) would allow one to determine the type of quadratic function that formed the gradient structure and the form of this structure. The possibility of creating gradient films with different laws ωn(n) and the high magnitude of the high-frequency magnetic susceptibility χn(n) at n<nc make these metamaterials promising for practical applications.

Reservoir Computing Using a Spin-Wave Delay-Line Active-Ring Resonator Based on Yttrium-Iron-Garnet Film

The authors demonstrate the use of a propagating spin waves for implementing a reservoir computing architecture. The proposed concept utilises an active ring resonator comprising a magnetic thin film delay line integrated into a feedback loop. These systems exhibit strong nonlinearity and delayed response behaviour, two important properties required for an effective reservoir computing implementation. In a simple design, we exploit the nonlinear damping of spin waves at different feedback gains to inject input data into the active ring resonator and use a microwave diode to read out the amplitude of the spin waves circulating in the ring. We employ two baseline tasks, namely the short term memory and parity check tasks, to evaluate the suitability of this architecture for processing time series data.

Investigation of Left-Handed Behavior in Ferromagnetic Cobalt Magnetic Vortex Structure Using Spin-Wave Resonances

Terahertz spintronics is an emerging field that bridges the boundary between magnetism and photonics, which make the magnetic material suitable for photonic applications. In this article, terahertz spin-wave resonances are used to investigate the effective permeability of left-handed behavior in an array of cobalt nanomagnetic vortices. The ultrafast magnetization and the toroidal moment of the cobalt nanomagnetic vortices play a major role in reducing losses in the left-handed metamaterial. The ultrafast magnetization dynamics of an array of cobalt nanomagnetic vortices are studied both analytically and numerically, and the results are used to study the variation of permeability as a function of frequency in the terahertz range.

Spin-wave oscillations in gradient ferromagnets: Exactly solvable models

The method of searching for the profiles of the gradient dependence of the material parameters of matter on the coordinates that allow the exact solution of wave equations, developed previously for electromagnetic and elastic waves, was generalized to spin waves in gradient ferromagnets. Such profiles were found and exact solutions of the wave equations for a ferromagnet with uniaxial magnetic anisotropy β(z) or exchange α(z) varying in space were obtained. The obtained solutions were used to develop the theory of spin-wave resonance in gradient thin magnetic films. The dependences of the eigenfunctions mn(z), the frequencies of the discrete spectrum ωn, and the high-frequency susceptibility χn on the number of spectral levels n were found. The cardinal differences between the spin-wave spectra of films with gradients β(z) and α(z) are shown. The variable anisotropy β(z) changes the shape of the energy potential of the magnetic film and leads to a change in the discrete spectrum for frequencies ωn(n) lower than the frequency of the gradient potential well or potential barrier ωc. The variable exchange α(z) does not change the shape of the energy potential. Spin-wave oscillations occur in a rectangular potential well created by the surfaces of the film, regardless of profile α(z). The discrete frequency spectrum ωn(n) is quadratic on n, or has negligible deviations from the quadratic, for all n. An analytical expression for the effective exchange parameter is obtained. Exact solutions of the Schrödinger equation with spatially dependent effective mass m(z) were found for the profile of m(z) inverse to the function of α(z).