Nonlinear Magnetoelastic Coupling Research Articles

Performance optimization for magnetoelectric antennas based on a multi-field coupling analysis model

This paper presents a multi-field coupling model for magnetoelectric (ME) antennas, encompassing a ME film, electrode layers, and a substrate featuring a cavity structure. This model accounts for the nonlinear magnetoelastic coupling within the radiation layer and employs a combined DC and AC simulation methodology to capture the antenna's radiation mechanism. Leveraging this multi-field coupling model, performance differences between the ME antenna and an ideal ME composite film are analyzed. By exploring optimization schemes based on multi-physics fields, electrode materials, and structural design, the ME antenna's radiation performance is significantly enhanced. The findings demonstrate that the complete antenna structure, with its increased thickness and cavity design, exhibits a lower resonance frequency and a higher converse ME (CME) coefficient compared to the ideal ME film. The optimal CME effect is achieved under proper external stimuli, leading to a broader 3 dB bandwidth. Expanding the cavity dimensions enhances the CME coefficient by 42% and reduces the resonance frequency due to decreased acoustic wave loss. Adopting electrode materials with higher acoustic impedance elevates the CME coefficient, yet narrows the bandwidth. Conversely, using silver (Ag) electrodes promotes a broader bandwidth. Additionally, ME antenna arrays are designed to broaden the bandwidth by 300%.

Analytical solutions for full-field radiations of magnetoelectric antennas with nonlinear magnetoelastic coupling

Analytical solutions for full-field radiations of magnetoelectric antennas with nonlinear magnetoelastic coupling

Magneto-elastic-optical coupling of Terfenol-D based optical fiber magnetic field sensors

A magneto-elastic-optical coupling model for Terfenol-D based single-mode optical fibers is proposed, in which the nonlinear magneto-elastic coupling characteristics of Terfenol-D is taken into consideration. The field-dependent material constants for magnetic coating is predicted and in good agreement with experimental results. The coupling effects of external stimuli (e.g. magnetic field and stress) on magneto-optic (MO) coupling coefficient of optical fibers are investigated for the first time. The results show that the relative phase change is enhanced by changing the thickness or Poisson’s ratio of constituent materials. More importantly, appropriate applied tensile/compressive stress can control the value of optimal bias field as well as enhance MO coupling coefficient of optical fibers under different magnetic fields. This research provides a method to evaluate and improve magnetic performance of the optical fiber magnetic field sensors consisting of giant magnetostrictive materials.

Effect of boundary conditions on magnetocapacitance effect in a ring-type magnetoelectric structure

By considering the nonlinear magneto-elastic coupling relationships of magnetostrictive materials, an analytical model is proposed. The resonance frequencies can be accurately predicted by this theoretical model, and they are in good agreement with experimental data. Subsequently, the magnetocapacitance effect in a ring-type magnetoelectric (ME) structure with different boundary conditions is investigated, and it is found that various mechanical boundaries, the frequency, the magnetic field, the geometric size, and the interface bonding significantly affect the capacitance of the ME structure. Further, additional resonance frequencies can be predicted by considering appropriate imperfect interface bonding. Finally, the influence of an external force on the capacitance is studied. The result shows that an external force on the boundary changes the capacitance, but has only a weak influence on the resonance frequency.

Electric-field-driven magnetization switching and nonlinear magnetoelasticity in Au/FeCo/MgO heterostructures

Voltage-induced switching of magnetization, as opposed to current-driven spin transfer torque switching, can lead to a new paradigm enabling ultralow-power and high density instant-on nonvolatile magnetoelectric random access memory (MeRAM). To date, however, a major bottleneck in optimizing the performance of MeRAM devices is the low voltage-controlled magnetic anisotropy (VCMA) efficiency (change of interfacial magnetic anisotropy energy per unit electric field) leading in turn to high switching energy and write voltage. In this work, employing ab initio electronic structure calculations, we show that epitaxial strain, which is ubiquitous in MeRAM heterostructures, gives rise to a rich variety of VCMA behavior with giant VCMA coefficient (~1800 fJ V−1m−1) in Au/FeCo/MgO junction. The heterostructure also exhibits a strain-induced spin-reorientation induced by a nonlinear magnetoelastic coupling. The results demonstrate that the VCMA behavior is universal and robust in magnetic junctions with heavy metal caps across the 5d transition metals and that an electric-field-driven magnetic switching at low voltage is achievable by design. These findings open interesting prospects for exploiting strain engineering to harvest higher efficiency VCMA for the next generation MeRAM devices.

A General Magnetoelastic Coupling Theory of Deformable Magnetized Medium Including Magnetic Forces and Magnetostriction Effects

From the viewpoint of energy, a general magnetoelastic coupling theory including magnetic forces and magnetostriction effects is proposed for deformable magnetized medium. Firstly, a Taylor series expansion of independent variables of stress and magnetization in the elastic Gibbs free energy function is applied to obtain a polynomial expression; and then based on the magnetoelastic coupling mechanism, appropriate transcendental functions are substituted for some terms in a polynomial constitutive relationship derived by way of substituting the polynomial Gibbs free energy function in thermodynamic equations to achieve a more compact magnetostrictive constitutive relationship. The numerical simulation exhibits that the predicted magnetostrictive strain and magnetization curves under various pre-stresses are in good agreement with the experimental data given by Kuruzar et al (1971) and Jiles et al (1984). Secondly, based on the above magnetization constitutive relationship, a general magnetic forces expression is presented according to the variational principle for the total energy functional of the coupling system of the 3-d deformable magnetized materials. It is found that for the case of linear isotropic ferromagnetic materials, the magnetic forces expression can be degenerated into the Zhou-Zheng Model (1999). Combining the above nonlinear magnetostrictive constitutive relationship and magnetic forces expression, a general nonlinear magnetoelastic coupling theory is presented in this paper for deformable magnetized medium.

Ab-initio modeling of nonlinear magnetoelastic coupling in epitaxial films

Abstract The second-order magnetoelastic effects observed with cantilever-bending-beam experiments on epitaxial cubic films are interpreted within the framework of the nonlinear theory of magnetoelasticity. The corresponding coupling coefficients are calculated ab initio and compared with the available measured data.

Nonlinear magnetoelastic coupling effects in a soft ferromagnetic material with a crack

In this paper, the magnetoelastic coupling effect in an infinite soft ferromagnetic material with a crack is analyzed. The nonlinear effect of magnetic field upon stress and the effect of the deformed crack configuration are taken into consideration. The coupling field is determined in the deformed configuration by regarding the deformed crack as an elliptical cylinder with its geometric coefficients, which are determined from a set of algebraic equations deduced from the displacements. The magnetic and stress fields near the crack tip are discussed for the case where both of the magnetic loading and the mechanical tension are present.

On the magnetoelastic contribution to the magnetic anisotropy of thin epitaxial Permalloy films: an ab initio study

Permalloy films are often used in the magnetic thin film technology. It is expected that in this material the magnetoelastic coupling of the magnetization to the epitaxial film strain does not produce undesired magnetic anisotropy, because the linear magnetoelastic bulk coefficient B 1 of Permalloy is near-zero. It is shown by means of the ab initio density functional electron theory that the nonvanishing nonlinear magnetoelastic couplings also do not lead to a considerable anisotropy. Explicit values for two of the nonlinear magnetoelastic coupling coefficients are given.

Nonlinear magnetoelastic effects in ultrathin epitaxial FCC Co(0 0 1) films: : an ab initio study

Those linear and nonlinear magnetoelastic coupling coefficients which determine the magnetostrictive stress and the strain-induced out-of-plane magnetic anisotropy in epitaxially grown FCC Co(0 0 1) films are calculated by the ab initio density functional electron theory. The nonlinear couplings have a strong effect on the change Δ σ 1 m of the in-plane magnetostrictive stress resulting from a change of the magnetization direction from [0 1 0] to [1 0 0], but a negligibly small effect on the out-of-plane anisotropy e MCA. The calculations confirm the experimental result that the measured out-of-plane anisotropy cannot be totally attributed to volume magnetoelastic effects. Estimates are given for the nonlinear magnetoelastic coupling coefficients m 1 γ,2 and m 2 γ,2 .

Magnetoelastic effects in ultrathin epitaxial Ni films: an ab initio study

The effect of the nonlinear magnetoelastic coupling on the magnetostrictive stress and the magnetic anisotropy of epitaxially grown ultrathin Ni films with large epitaxial strain is investigated by the ab initio density functional electron theory. The nonlinear coupling has a considerable influence on the magnetostrictive stress, in agreement with the experimental results from the optical bending beam technique, but a weaker influence on the stress-induced magnetic anisotropy. Estimates are given for the nonlinear magnetoelastic coupling coefficients m 1 γ,2 and m 2 γ,2 . The results are compared with those for Fe.

Nonlinear magnetoelastic coupling coefficients from simultaneous measurements of magnetostrictive stress and anisotropy in epitaxial magnetic films

The magnetic properties of epitaxially grown magnetic thin films used for magnetic storage, in magnetostrictive sensors or magnetostrictive random access memories are sometimes strongly influenced by the linear and nonlinear magnetoelastic coupling of the magnetization to the epitaxial strains. However, the experimental information on nonlinear magnetoelastic coupling coefficients is extremely scarce. In this letter, the theoretical background is provided as to how to extract this information from a combination of the well-established magnetostrictive stress and anisotropy experiments.

Nonlinear magnetoelastic coupling coefficients in Fe from an ab initio calculation

Based on the nonlinear theory of magnetoelasticity, a general method is developed which allows the determination of first-order and second-order magnetoelastic coefficients of a magnetic material from the ab initio calculation of magnetocrystalline anisotropy energies as functions of various modes of imposed strain. Explicit results are given for BCC Fe. The data confirm the hints from the magnetostrictive stress experiments that nonlinear magnetoelastic coupling effects are essential for the magnetic properties of thin epitaxial magnetic films with large epitaxial strains.

Enhancement of Mode Locking of Spin Waves at Low Temperatures

Investigations of mode locking of spin waves in YIG by nonlinear magnetoelastic coupling have been extended to low temperatures. Due to an increase of the spin-wave linewidth of YIG at low temperature, more spin-wave modes can be excited and, consequently, stronger mode-locking effects are observed. In our experiment more than 10 modes of spin waves have been mode locked. The variation of number of modes as a function of temperature is presented. In addition, a pickup coil is placed near the sample to measure any changes in mz. Since, for small perturbations, mz = 1 − ½ (mx1+my2), beating among different spin-wave modes will cause time variations of mz at the various beat frequencies. An enchancement of the harmonic content is observed upon the application of a mode-locking acoustic wave.