Magnetoacoustic Interaction Research Articles

Highly sensitive surface acoustic wave magnetic field sensor based on the loss mechanism

Currently, the surface acoustic wave (SAW) magnetic field sensing technique utilises the SAW velocity/frequency mechanism of magnetoacoustic interaction as an indicator of the magnetic sensitivity mechanism. However, this method has low sensitivity and poor stability. To address this problem, a dynamic magnetoelastic coupling theoretical model is constructed to theoretically simulate the influence of the ΔE effect of magnetically sensitive thin films on SAW propagation attenuation. This study describes a high-sensitivity SAW magnetic field sensing mechanism based on magnetoacoustic attenuation. The simulation results show a clear relationship between the acoustic propagation loss and external magnetic field, indicating a structure-property relationship. An amorphous soft magnetic material (Fe90Co10)78Si12B10 was used as a magnetically sensitive thin film due to its high permeability, low coercivity (Hc), low hysteresis, ease of magnetisation and demagnetisation. SAW magnetosensitive device operating on a frequency of 200 MHz has been experimentally developed using a standard semiconductor photolithography process. A SiO2 layer was deposited on a 36° YX-LiTaO3 substrate as a waveguide, and a (Fe90Co10)78Si12B10 layer was on the top of the propagation area as a magnetosensitive film. The experimental results showed that the acoustic loss change due to the magnetic field variation was 4.63 dB within a magnetic field range of 0 Oe to ±10 Oe, which agreed with the theoretical results. The sensor had a sensitivity of 0.7546 dB Oe−1 within the range of 0–4 Oe and the lower detection limit of magnetic fields was 0.272 Oe, low hysteresis error of 0.54%, multiple repeatability error of 0.13%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

Acoustic Waves Induced by Einstein-de Haas Effect in the Ultrafast Core Reversal of Magnetic Vortex.

The interaction between acoustic wave and magnetization in ferromagnetic thin films has attracted great attention due to its interesting physics and potential applications. However, up to now, the magneto-acoustic interaction has mainly been studied on the basis of magnetostriction. In this Letter, we develop a phase field model of magneto-acoustic interaction based on the Einstein-de Haas effect, and predict the acoustic wave during the ultrafast core reversal of magnetic vortex in a ferromagnetic disk. Because of the Einstein-de Haas effect, the ultrafast change of magnetization at the vortex core leads to a large mechanical angular momentum, which induces a body couple at the vortex core and excites a high-frequency acoustic wave. Moreover, the displacement amplitude of the acoustic wave is highly dependent on the gyromagnetic ratio. The smaller the gyromagnetic ratio is, the larger the displacement amplitude is. The present work not only provides a new mechanism for dynamic magnetoelastic coupling but also sheds new insights on the magneto-acoustic interaction.

Coupling of Lamb Waves and Spin Waves in Multiferroic Heterostructures

In this work, we investigate magneto-acoustic attenuation in thin film multiferroic Lamb wave delay lines. By leveraging magneto-acoustic interactions, multiferroics have potential to realize passive chip-scale alternatives to bulky ferrite devices. For the first time, magnetic field dependence of magneto-acoustic interactions in multiferroic Lamb wave devices is characterized. Multiferroic heterostructures of aluminum nitride and cobalt iron boron are fabricated into Lamb wave delay lines operating at 7.492 GHz to study the effect of strain nonuniformity on the multiferroic coupling. The attenuation of the Lamb waves is characterized as a function of the magnitude and angle of an applied in-plane bias magnetic field. It is found that the bias magnitude for peak attenuation is a strong function of angle, indicating that it is due to coupling between the Lamb waves and spin wave modes. This is in contrast with current models of attenuation in multiferroic SAW delay lines, where the uniform surface strains couple to ferromagnetic resonance, which has no angular dependence on the in-plane bias field magnitude. These results are the first steps towards passive chip-scale alternatives to ferrite devices utilizing Lamb wave devices, which have better coupling and scalability than their SAW counterparts. [2020-0114]

ChemInform Abstract: Ultrafast Magnetization Dynamics of Nanostructures

AbstractReview: 122 refs.

ChemInform Abstract: Spin Wave Acoustics of Antiferromagnetic Structures as Magnetoacoustic Metamaterials

AbstractReview: 247 refs.

Tunneling and inversion symmetry in single-molecule magnets: The case of theMn12wheel molecule

We present a detailed study of the influence of various interactions on the spin quantum tunneling in a Mn12 wheel molecule. The effects of single-ion and exchange (spin-orbit) anisotropy are first considered, followed by an analysis of the roles played by secondary influences, e.g. disorder, dipolar and hyperfine fields, and magnetoacoustic interactions. Special attention is paid to the role of the antisymmetric Dzyaloshinski-Moriya (DM) interaction. This is done within the framework of a 12-spin microscopic model, and also using simplified dimer and tetramer approximations in which the electronic spins are grouped in 2 or 4 blocks, respectively. If the molecule is inversion symmetric, the DM interaction between the dimer halves must be zero. In an inversion symmetric tetramer, two independent DM vectors are allowed, but no new tunneling transitions are generated by the DM interaction. Experiments on the Mn12 wheel can only be explained if the molecular inversion symmetry is broken, and we explore this in detail using both models, focussing on the asymmetric disposition and rounding of Berry phase minima associated with quantum interference between states of opposite parity. A remarkable behavior exists for the `Berry phase zeroes' as a function of the directions of the internal DM vectors and the external transverse field. A rather drastic breaking of the molecular inversion-symmetry is required to explain the experiments; in the tetramer model this requires a reorientation of the DM vectors on one half of the molecule by nearly 180 degrees. This cannot be attributed to sample disorder. These results are of general interest for the quantum dynamics of tunneling spins, and lead to some interesting experimental predictions.

Magnetoacoustic SAW interaction in YIG films

The magnetoacoustic SAW interaction has been experimentally investigated for yttrium-iron garnet films placed on gallium gadolinium garnet substrates. In this paper, we propose a new approach to the analysis of hysteresis dependencies which consist of two branches for different directions of magnetic field variation. For each of the branches, even and odd portions were separated. The even portions were shown to be related to magnetostriction and the odd ones to DeltaE-effect and magnetostriction linearized internal magnetic field of domains.

Acoustic excitation of nuclear spin waves in the easy-plane antiferromagnetic material KMnF3

Ultrasound damping at T=4.2 K in single crystal easy-plane antiferromagnetic KMnF3 is studied experimentally as a function of the magnitude and direction of a constant magnetic field H at frequencies of 640–670 MHz, corresponding to the frequencies of nuclear spin waves. Two experimental situations are examined: in the first, the vector H lies in the easy magnetization plane (001), and in the second, H forms an angle with (001). For longitudinal ultrasound waves propagating along the hard magnetization axis [001], it is found that the damping depends resonantly on the magnitude of the field H. In the first case a single damping maximum is observed, and in the second, two damping peaks that are well resolved with respect to the field. The angular dependence of the resonance damping signals on the direction of the constant magnetic field is found to have a 90° periodicity in all cases. The observed effects are explained by resonant ultrasonic excitation of nuclear spin waves. On the basis of an analysis of the magnetoacoustic interaction energy, it is shown that in the first case, nonzero oscillations of the antiferromagnetism vector L occur only in the basal plane, while in the second, oscillations of L occur both in the basal and a vertical plane, which are associated, respectively, with two branches of the nuclear spin waves. It is also shown that the 90° periodicity in the angular dependence of the damping signals is associated with a fourth order [001] axis.

Frequency Dependence of Magnetoacoustic Interaction under Applied Stress.

Frequency dependence of magnetoacoustic interaction was experimentally investigated for JIS-SS400 low-carbon steel. Velocity of an elastic wave which propagates in a ferromagnetic material slightly varies when an external magnetic field is applied. This is called the magnetoacoustic interaction. This occurs because the elastic properties depend on the magnetic domain structure, which is affected by both the external magnetic field and the stress. Consequently, the magnetoacoustic interaction is dependent on the stress, and it can be applied to nondestructive stress measurements. In this study, the magnetically induced change in the longitudinal wave velocity is measured under various stress levels. The frequency dependence is explained qualitatively in terms of the domain wall motion and the rotational vibration of the domain magnetization. Effects of texture and annealing are also investigated. Discussion is presented on the applicability to the nondestructive residual stress measurement.

Observation of higher-order Floquet modes in magneto-acoustic interactions

The higher-order space-time Floquet harmonics resulting from the scattering of magnetostatic waves by surface acoustic waves have been investigated. Experimental results are reported on the observation of these higher-order modes in magneto-acoustic Bragg interactions in magnetic films. The results are compared to the theoretical predictions based on the coupled-mode analysis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nondestructive residual stress measurement in steel using magnetoacoustic interactions.

In ferromagnetic materials, ultrasonic velocity varies with both stress and external magnetic field. This phenomenon occurs due to the magnetoelastic interactions, and it is called magnetically induced velocity change (MIVC). The behavior of MIVC depends on the stress, magnetic field, ultrasonic mode (longitudinal or shear), and their relative orientation including the polarization direction of the shear wave. Its magnitude is of the order of 10-5, being comparable with the acoustoelastic effects. In the present study, the MIVC for longitudinal and polarized shear waves were first measured with mild steel specimens for the changing magnetic fields applied parallel or perpendicular to uniaxial stresses. The MIVC curves thus obtained showed salient dependence on the stress. They were then used to nondestructively evaluate the thermomechanical residual stress introduced by gas cutting. The results agreed with the strain gage measurements and the conventional acoustoelastic methods, both destructive, showing the usefulness of the MIVC method to measure residual stresses nondestructively. The MIVC was found to be insensitive to the micros-tructures.

Niobium Fermi surface and the magnetoacoustic interaction: Polarization selectivity

The magnetoacoustic interaction for field $\stackrel{\ensuremath{\rightarrow}}{H}$ normal to propagation vector $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$ has been studied in high-purity niobium at frequencies extending to 650 and 430 MHz for longitudinal and transverse waves, respectively. Fermi-surface calipers determined for $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}\ensuremath{\parallel}[100]$ and $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\epsilon}}\ensuremath{\parallel}[010]$ agree within about 2% with the augmented-plane-wave theoretical values for the distorted ellipsoids. Also, an interesting and useful "caliper-selectivity" mechanism operative in the transverse-wave case was observed which, for particular orientations of wave polarization $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\epsilon}}$, served to isolate individual calipers so that the calipers corresponding to a single Fermi sheet were swept out as $\stackrel{\ensuremath{\rightarrow}}{H}$ was rotated through 360\ifmmode^\circ\else\textdegree\fi{}. The corresponding presence of a single period in the oscillations at all field angles permitted relaxation of the number of oscillations required for precise determination of the electron momenta.

Magnetoacoustic Excitation of Radio-Frequency Resonances and Echoes in Magnetic Materials

Continuous spectra of resonances are observed when some ferromagnetic substances are examined with cw or spin-echo rf spectrometers. These resonances have previously been assigned to domain-wall motion; evidence is presented here to show rather that they are magnetically excited acoustic vibrations. An explanation of the manner in which a nonlinear magnetoacoustic interaction allows the production of echoes in an otherwise linear system is presented. A means of suppressing these resonances to facilitate the study of nuclear magnetic resonances in magnetic materials is demonstrated.

Magnetoelastic Coupling Constants of Terbium and Europium Iron Garnets

The purpose of this paper is twofold: (1) to present data on the magnetoelastic constants of rare-earth iron garnets, a subject which for various reasons has been little studied thus far, and (2) to describe a new method for obtaining these constants which is applicable to many ferromagnetic insulators and does not require the use of strain gauges. The new method was developed from a study of the coupling introduced between long wavelength acoustic modes and long wavelength spin-wave modes by ions in which the orbital moment is not quenched, such as rare-earth ions, Co2+, and Fe2+. The effect of the coupling caused by such ions is observed as a magnetic field dependence of the resonant frequency of an acoustic resonator made from the given material, even above dc saturation. The acoustic Q above dc saturation is also field-dependent. A theory has been obtained which explains the observed field dependences of both v(H) and Q(H) as well as other important features of the magnetoacoustic interaction. It will appear elsewhere.1 One of the results of this theory is a relation between the cubic magnetoelastic constants, B1 and B2, and the acoustic resonant frequency v of a thin disk vibrating in a thickness shear mode. For a (110) disk with the external field H0 in the plane along [100] and the rf driving field perpendicular to the disk, we obtain ν=ν∞(1−B222c44MHeff),where Heff=H0+Hanis+4πM, and c44 is the usual shear elastic modulus, which may be obtained directly from v∞ and the thickness of the disk. Equation (1) applies to the mode with displacement along [100]. B1 is obtained similarly, only now H0 is along [110] in the plane, and the shear displacement is along [110]. Here we have ν=ν∞(1−B122c44MHeff). All data thus far have given excellent fits to these equations as Heff is varied, making it easy to obtain the unknown constants. It should be noted that Eqs. (1) and (2) are high-temperature approximations and at low temperatures will not in general be as simple. For TbIG and EuIG at room temperature we find the following (all in ergs cm−3): For TbIG, |B1|≤3.5×106, |B2|=30×106; and for EuIG, |B1|=45×106 and |B2|≤4.2×106. The signs must still be determined from strain gauge measurements. The observed reversal of the magnetoelastic anisotropy (ratio of B1 to B2) is being investigated, as well as the temperature dependences of B1 and B2.