Spin Wave Resonance Research Articles

Ferromagnet/Superconductor Hybridization for Magnonic Applications

AbstractIn this work, a new hybridization of superconducting and ferromagnetic orders is demonstrated, promising for magnonics. By measuring the ferromagnetic and spin wave resonance absorption spectra of a magnetostatically coupled permalloy/niobium bilayer at different temperatures, magnetostatic spin wave resonances with unconventional dispersion are observed. The mechanism behind the modified dispersion, confirmed with micromagnetic simulations, implies screening of the alternating magnetostatic stray fields of precessing magnetic moments in the ferromagnetic layer by the superconducting surface in the Meissner state.

Magnetic Properties and Electronic Structure of Co/Zr Multilayers

We investigate the magnetic and electronic properties of Co/Zr multilayers with an emphasis on the interfacial effects. The saturation magnetization, coercivity, and uniaxial anisotropy depend significantly on Co thickness. Spin-wave resonance modes were observed, and the change of resonant field as a function of mode number (n) obeys the so-called n2 law. The interlayer coupling constant was determined. The electronic properties of the interfacial alloys were studied using the WIEN2k code, employing the density functional theory. Calculations describe satisfactorily the observed magnetic behaviour. The influence of pressure on the magnetic properties of the interfacial Co1−xZrx alloys was investigated in which we demonstrate that the ferromagnetism is altered by pressure.

Spin-Wave Resonance in Ge : Mn Thin Films with Percolation Magnetic Ordering

The mechanism of excitation and propagation of spin waves in Ge: Mn thin films with different nominal manganese concentrations (2, 4, and 8 at % Mn) with percolation magnetic ordering is explored. Concentration dependencies of Curie temperature TC(n) and spin wave rigidity D(n) are determined, which enables to find the index of correlation distance. An exotic percolation magnetic state of samples of Ge: Mn thin films is confirmed by rectifying experimental dependences D(n) and D/TC(n) in coordinates accepted in the percolation theory.

Spin wave resonance in symmetrical/asymmetrical bilayer ferromagnetic films

The dependence of spin wave resonance (SWR) frequency on the surface anisotropy, the interlayer coupling, the ferromagnetic layer thickness and the external magnetic field in the bilayer ferromagnetic film have been investigated by using the linear spin wave approximation and Green’s function technique. We find that the SWR frequency of the ferromagnetic bilayer film are shifted to higher values corresponding to those of above factors, respectively. The lowest four modes can be controlled by the surface anisotropy of A, B layer and the symmetry of the film. The SWR frequency of the energetically lowest mode is no affected except for applied magnetic field. A notable rapidly increasing behavior appears in frequency with the increasing of interlayer coupling.

Shape anisotropy in patterned ferromagnetic GaMnAsP films with perpendicular anisotropy

We investigate the effects of physical dimensions on the behavior of magnetic anisotropy in lithographically-fabricated nanoscale squares of the ferromagnetic semiconductor GaMnAsP using SQUID magnetometry and ferromagnetic resonance (FMR). Both measurements show that perpendicular magnetic anisotropy is strongly affected by the size of the ferromagnetic nano-scale elements, while their Curie temperature and their in-plane anisotropy remain unchanged in the range studied. In addition to uniform-mode FMR, we observe a series of spin-wave resonances, whose analysis suggests that surface anisotropy plays an important role in determining the properties of nanoscale magnets.

Spin-wave resonances in bismuth orthoferrite at high temperatures

Spin-wave resonances in pelletized powder of bismuth orthoferrite (${\mathrm{BiFeO}}_{3}$) were studied in transmission spectroscopy at frequencies of 0.1--0.75 THz and in the temperature range of 300--650 K. A vector network analyzer with frequency extenders was used in conjunction with temperature scans. We extended the experimental coverage of spin-wave resonances in ${\mathrm{BiFeO}}_{3}$ up to almost the N\'eel temperature. We observed that ${\mathrm{\ensuremath{\Psi}}}_{1}^{(1)}$ and ${\mathrm{\ensuremath{\Psi}}}_{1}^{(2)}$ modes are degenerate around 420 K due to the temperature dependences of the magnetic anisotropy and the Dzyaloshinskii-Moriya interaction.

Spin-Wave Resonance in Chemically Deposited Fe-Ni Films: Measuring the Spin-Wave Stiffness and Surface Anisotropy Constant

Single-layer Fe x Ni1 - x thin magnetic films have been investigated by the spin-wave resonance technique in the entire concentration range. The surface anisotropy and exchange stiffness constants for the films with a Ni content from 30 to 80 at % have been measured from the experimental standing spin wave spectra. The surface exchange spin wave penetration depth δ C = 20–30 nm has been determined from the dependences of the surface anisotropy and exchange coupling constants on the Fe20Ni80 film thickness in the range of 250–400 nm.

Effects of Symmetry Breaking in Resonance Phenomena

We show that resonance phenomena can be treated as nonequilibrium phase transitions. Resonance phenomena, similar to equilibrium phase transitions, are accompanied by some kind of symmetry breaking and can be characterized by order parameters. This is demonstrated for spin-wave resonance, helicon resonance, and spin-reversal resonance.

INVESTIGATION OF ANGULAR AND TEMPERATURE DEPENDENCE OF SPIN-WAVE RESONANCE SPECTRA IN MULTILAYER MAGNETIC FILMS

In this letter we study the dependences of the resonance field Hn and the linewidth 2ΔHn of the spin-wave resonance (SWR) modes in two-layer ferrite-garnet films with dissipative and mixed spinpinning mechanisms. It is established that for films with a dissipative mechanism of spin pinning, the increase in the linewidth at ΘH = 35° is associated with the maximum misorientation between the external magnetic field and the direction of the equilibrium magnetization of the sample. For films with a mixed spin-pinning mechanism, an increase in the linewidth 2ΔHn with increasing angle ΘH is associated with an increase in the depth of penetration of the spin wave into the pinning layer for such films. On the temperature dependence of the linewidth 2ΔHn for samples with a mixed fixation mechanism at a perpendicular orientation, an increase in the width of the absorption peak lines is observed. And with an increase in the peak number, the maximum of the linewidth shifts to the low-temperature region. With parallel orientation, the linewidth 2ΔHn in a wide temperature range from 20°C to 200°C remains practically unchanged.

Спин-волновой резонанс в химически осажденных Fe-Ni пленках: измерения спин-волновой жесткости и константы поверхностной анизотропии

AbstractSingle-layer Fe_ x Ni_1 - x thin magnetic films have been investigated by the spin-wave resonance technique in the entire concentration range. The surface anisotropy and exchange stiffness constants for the films with a Ni content from 30 to 80 at % have been measured from the experimental standing spin wave spectra. The surface exchange spin wave penetration depth δ_ C = 20–30 nm has been determined from the dependences of the surface anisotropy and exchange coupling constants on the Fe_20Ni_80 film thickness in the range of 250–400 nm.

Ferromagnetic resonance and spin-wave resonances in GaMnAsP films

A series of Ga1-xMnxAs1-yPy films grown by MBE on GaAs (100) substrates was systematically studied by ferromagnetic resonance (FMR). Magnetic anisotropy parameters were obtained by analyzing the angular dependence of the FMR data. The results clearly show that the easy axis of the films shifts from the in-plane [100] direction to the out-of-plane [001], indicating the emergence of a strong tensile-strain-induced perpendicular anisotropy when the P content exceeds y ≈ 0.07. Multiple resonances were observed in Ga1-xMnxAs1-yPy films with thicknesses over 48 nm, demonstrating the existence of exchange-dominated non-propagating spin-wave modes governed by surface anisotropy.

Investigation of Magnetic Properties of Multilayer Thin Films with Spin-Wave Resonance

A theory has been developed to simulate spin-wave resonance (SWR) modes in the multilayer systems consisting of alternate magnetic and nonmagnetic layers. An equation of motion of magnetization with Gilbert-type damping parameter for simulating SWR modes was used. It has been realized that the theory developed for the magnetic multilayer films is suitable to study the spin dynamics and extract various magnetic parameters. It has been shown that SWR modes strongly depend on an effective magnetic anisotropy constant (K eff), interlayer exchange coupling constant (A 12) and effective magnetization (M eff). The nature of the effective magnetic anisotropy and interlayer exchange coupling constants has been investigated by using the developed SWR theory in detail. The separation between optic and acoustic modes strongly depends on the magnitude of the interlayer exchange coupling constant, whereas the relative position of the acoustic and optic modes depends on the sign of $A_{12}$ . With increasing the interlayer exchange coupling constant, the resonance field of the optic mode decreases (increases) for ferromagnetic (antiferromagnetic) coupling. When the effective magnetic anisotropy constant increases, the resonance field of the acoustic and optic modes increases for both the ferromagnetic and antiferromagnetic couplings. The increasing of the effective magnetization results in decreasing of the resonance field of SWR mode at parallel geometry, whereas that of SWR mode increases at the perpendicular geometry. The results are compatible to the other theories and experimental results.

Measurement of shot noise in magnetic tunnel junction and its utilization for accurate system calibration

This work presents a technique to calibrate the spin torque oscillator (STO) measurement system by utilizing the whiteness of shot noise. The raw shot noise spectrum in a magnetic tunnel junction based STO in the microwave frequency range is obtained by first subtracting the baseline noise, and then excluding the field dependent mag-noise components reflecting the thermally excited spin wave resonances. As the shot noise is guaranteed to be completely white, the total gain of the signal path should be proportional to the shot noise spectrum obtained by the above procedure, which allows for an accurate gain calibration of the system and a quantitative determination of each noise power. The power spectral density of the shot noise as a function of bias voltage obtained by this technique was compared with a theoretical calculation, which showed excellent agreement when the Fano factor was assumed to be 0.99.

Topological spin dynamics in cubic FeGe near room temperature

Understanding spin-wave dynamics in chiral magnets is a key step for the development of high-speed, spin-wave based spintronic devices that take advantage of chiral and topological spin textures for their operation. Here, we present an experimental and theoretical study of spin-wave dynamics in a cubic B20 FeGe single crystal. Using the combination of waveguide microwave absorption spectroscopy (MAS), micromagnetic simulations, and analytical theory, we identify the resonance dynamics in all magnetic phases (field polarized, conical, helical, and skyrmion phases). Because the resonance frequencies of specific chiral spin textures are unique, a quantitative agreement between our theoretical predictions and experimental findings for all resonance frequencies and spin wave modes enables us to unambiguously identify chiral magnetic phases and to demonstrate that MAS is a powerful tool to efficiently extract a magnetic phase diagram.

Magnetically tunable high-Q spin-wave optoelectronic single-loop resonator

Resonant properties of a spin-wave optoelectronic single-loop resonator are experimentally investigated. The resonator is composed of a spin-wave delay line and a microwave photonic delay line based on a single-mode optical fiber. This circuit is equivalent to a comb filter. The microwave photonic delay line provides the main contribution to the delay time and defines mostly the free spectra range (FSR). The spin-wave delay line realizes the reconfiguration of resonator bandwidth and its frequency tuning. Influences of delay time and amplifier gain coefficient on quality-factor are analyzed.

Localized spin-wave resonance modes of ferromagnetic microstrips in the field of a magnetic probe

Some results of the micromagnetic modeling of forced magnetization oscillations in planar microstrips of NiFe with easy plane anisotropy and Co/Pt with perpendicular easy axis anisotropy in the field of a magnetic spherical probe are considered. It has been shown that the probe field provokes the appearance of a hedgehog–antivortex coupling state in the NiFe strips, due to its lateral components and a skyrmion magnetization state in the Co/Pt layer. These effects destroy spatial magnetization oscillations in the microstrips and lead to the appearance of additional resonances in the spectrum of oscillations corresponding to the modes localized in the probe field.

Spin-Current Manipulation of Photo-Induced Magnetization Dynamics in Heavy Metal/Ferromagnet Double Layer-Based Nanostructures

Spin currents offer a way to control static and dynamic magnetic properties, and therefore they are crucial for next-generation MRAM devices or spin-torque oscillators. Manipulating the dynamics is especially interesting within the context of photo-magnonics. In typical $3d$ transition metal ferromagnets like CoFeB, the lifetime of light-induced magnetization dynamics is restricted to about 1 ns, which e.g. strongly limits the opportunities to exploit the wave nature in a magnonic crystal filtering device. Here, we investigate the potential of spin-currents to increase the spin wave lifetime in a functional bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum (Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer generates a transverse spin current when a lateral charge current passes through the strip. Using time-resolved all-optical pump-probe spectroscopy, we investigate how this spin current affects the magnetization dynamics in the adjacent CoFeB layer. We observed a linear spin current manipulation of the effective Gilbert damping parameter for the Kittel mode from which we were able to determine the system's spin Hall angles. Furthermore, we measured a strong influence of the spin current on a high-frequency mode. We interpret this mode an an exchange dominated higher order spin-wave resonance. Thus we infer a strong dependence of the exchange constant on the spin current.

Magnetic phases in thin films of Ni–Fe(Co)–Ga ferromagnetic shape memory alloy

1 µm-thick polycrystalline thin films of the ferromagnetic shape memory alloy, Ni49.7Fe17.4Co4.2Ga28.7 (at.%), were sputter-deposited on MgO(0 0 1) substrates heated at 773 K. The films’ structure, magnetic properties and transformation behavior have been characterized. They exhibit both forward and reverse martensitic transformations at 218 K and 232 K, respectively. Ferromagnetic resonance and x-ray diffraction measurements discerned three ferromagnetic phases: cubic L21-ordered austenite, tetragonal martensite and disordered cubic γ-phase. The latter phase showed a unique spin-waves resonance spectrum, enabling estimation of the value of the exchange stiffness constant equal to A = 0.7 × 10−6 erg cm−1.

Ferromagnetic resonance of 2D array of magnetic nanocaps

Nanostructured Co and permalloy films are fabricated on top of a polymethyl methacrylate (PMMA) colloidal crystals by magnetron sputtering. The influence of the geometry of the samples on the ferromagnetic resonance spectra is studied. A number of spin-wave resonances are found in the nanostructured system, while only a single resonance is observed in the spatially uniform flat film. The number of the observed resonance peaks increases with both the period of the colloidal crystal (120÷340nm) and the film thickness (20÷90nm). The micromagnetic simulations of the system show that the excited spin-wave modes are nonreciprocal because of nonzero toroidal momentum of the magnetization of the system.

Spin-wave resonance frequency in ferromagnetic thin film with interlayer exchange coupling and surface anisotropy

We have investigated the dependence of spin-wave resonance(SWR) frequency on the surface anisotropy, the interlayer exchange coupling, the ferromagnetic layer thickness, the mode number and the external magnetic field in a ferromagnetic superlattice film by means of the linear spin-wave approximation and Green's function technique. The SWR frequency of the ferromagnetic thin film is shifted to higher values corresponding to those of above factors, respectively. It is found that the linear behavior of SWR frequency curves of all modes in the system is observed as the external magnetic field is increasing, however, SWR frequency curves are nonlinear with the lower and the higher modes for different surface anisotropy and interlayer exchange coupling in the system. In addition, the SWR frequency of the lowest (highest) mode is shifted to higher (lower) values when the film thickness is thinner. The interlayer exchange coupling is more important for the energetically higher modes than for the energetically lower modes. The surface anisotropy has a little effect on the SWR frequency of the highest mode, when the surface anisotropy field is further increased.