Magnetoelastic Effects Research Articles

Exchange magnetostriction in two-dimensional antiferromagnets.

Magnetostriction, coupling between the mechanical and magnetic degrees of freedom, finds a variety of applications in magnetic actuation, transduction and sensing1,2. The discovery of two-dimensional layered magnetic materials3-8 presents a new platform to explore the magnetostriction effects in ultrathin solids. Here we demonstrate an exchange-driven magnetostriction effect in mechanical resonators made of two-dimensional antiferromagnetic CrI3. The mechanical resonance frequency is found to depend on the magnetic state of the material. We quantify the relative importance of the exchange and anisotropy magnetostriction by measuring the resonance frequency under a magnetic field parallel and perpendicular to the easy axis, respectively. Furthermore, we show efficient strain-tuning of the internal magnetic interactions in two-dimensional CrI3 as a result of inverse magnetostriction. Our results establish the basis for mechanical detection and control of magnetic states and magnetic phase transitions in two-dimensional layered materials.

Extreme Subwavelength Magnetoelastic Electromagnetic Antenna Implemented with Multiferroic Nanomagnets

AbstractAntennas typically have emission/radiation efficiencies bounded by A/λ2(A < λ2) where A is the emitting area and λ is the emitted wavelength. That makes it challenging to miniaturize antennas to extreme subwavelength dimensions without severely compromising their efficiencies. To overcome this challenge, an electromagnetic (EM) antenna is actuated with a surface acoustic wave (SAW) whose wavelength is about five orders of magnitude smaller than the EM wavelength at the same frequency. This allows to implement an extreme subwavelength EM antenna, radiating an EM wave of wavelength λ = 2 m, whose emitting area is ≈10−8 m2 (A/λ2 = 2.5 × 10−9), and whose measured radiation efficiency exceeds the A/λ2 limit by over 105. The antenna consists of magnetostrictive nanomagnets deposited on a piezoelectric substrate. A SAW launched in the substrate with an alternating electrical voltage periodically strains the nanomagnets and rotates their magnetizations owing to the Villari effect. The oscillating magnetizations emit EM waves at the frequency of the SAW. These extreme subwavelength antennas that radiate with efficiencies a few orders of magnitude larger than the A/λ2 limit allow drastic miniaturization of communication systems.

Spin Hall magnetoresistance in antiferromagnetic insulators

Antiferromagnetic materials promise improved performance for spintronic applications as they are robust against external magnetic field perturbations and allow for faster magnetization dynamics compared to ferromagnets. The direct observation of the antiferromagnetic state, however, is challenging due to the absence of a macroscopic magnetization. Here, we show that the spin Hall magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic spin structure via simple electrical transport experiments by investigating the easy-plane antiferromagnetic insulators α−Fe2O3 (hematite) and NiO in bilayer heterostructures with a Pt heavy-metal top electrode. While rotating an external magnetic field in three orthogonal planes, we record the longitudinal and the transverse resistivities of Pt and observe characteristic resistivity modulations consistent with the SMR effect. We analyze both their amplitude and phase and compare the data to the results from a prototypical collinear ferrimagnetic Y3Fe5O12/Pt bilayer. The observed magnetic field dependence is explained in a comprehensive model, based on two magnetic sublattices and taking into account magnetic field-induced modifications of the domain structure. Our results show that the SMR allows us to understand the spin configuration and to investigate magnetoelastic effects in antiferromagnetic multi-domain materials. Furthermore, in α−Fe2O3/Pt bilayers, we find an unexpectedly large SMR amplitude of 2.5×10−3, twice as high as for prototype Y3Fe5O12/Pt bilayers, making the system particularly interesting for room-temperature antiferromagnetic spintronic applications.

Strong phonon interaction between two distant magnetic films inserted into a cavity

Phonon and magnon excitations can be modulated by magnetoelastic and magneto-optical coupling effects, respectively. The photons not only mediate the interaction between two distant magnetic films inserted into a cavity, but also affect the phonon excitations in each film by the magnetoelastic coupling. In this work, an indirect interaction mechanism is presented for the phonons in two distant magnetic films inserted into a cavity. Although the phonons in no way pass through a very long distance from one film to the other in a vacuum environment, they can establish a correlation between two films through the magneto-optical and magnetoelastic couplings in each film. This really corresponds to an indirect interaction. In this work, the relationship between the phonon interaction and the laser intensity is studied using a quantum theory. It is found that when the laser frequency is equal to magnon frequency and the laser intensity is in a certain range, this phonon interaction energy takes very large negative values so as to satisfy the application requirement. According to a generating functional integral approach, a formula for the phonon interaction energy is derived, and an experimental approach to detect this effect is suggested. This indirect interaction effect of phonons not only adds to our understanding of the essence of matter interaction, but also reveals some potential applications to the heat management of electronic devices, long-range transfer of heat energy, and ultrasonic signal transmission in a vacuum environment.

Mechanism of Controllable Force Generated by Coupling Inverse Effect of Piezoelectricity and Magnetostriction

A method based on piezoelectric and magnetostrictive coupling inverse effect to generate precise controllable force is proposed to meet the requirement of manipulation force control in ultra-precision machining and assembly process. According to the principle of magnetic flux continuity, combine with the characteristics of piezoelectric and magnetostrictive inverse effects, the working mechanism of force generation is analyzed, and the theoretical model of the relationship between output force and parameters which include material characteristics, geometric parameters, working voltage of piezoelectric ceramics is established. An experimental device consisting of piezoelectric ceramic driving power supply, strain gauge, static strain tester, micro laser displacement sensor, force sensor, data acquisition card and magnetic force control component is developed. The relationship between output magnetic force and air gap or working voltage are studied by experiment and simulation. The results show that the output force variations of simulation and experiment are close. The output magnetic force fluctuation is small and with good stability. It verifies the consistency and correctness of the theoretical, simulation and experimental results.

Microstructure‐Enhanced Inverse Magnetostrictive Effect in Fe–Co Alloy Wires

Polycrystalline magnetostrictive alloys with a combination of high stiffness and strength and large magnetostriction are desirable for various smart applications, including energy harvesters and microscale sensors and actuators. However, the in‐depth understanding of the microstructure–property relationship in these alloys is still limited due to the complexity of their grain geometry, multi‐objective design requirements, and the few experimental verifications available. Herein, the correlation between the power generation properties and microstructures controlled by heat treatment in Fe29Co71 (at%) alloys is investigated. As a result, the Fe–Co alloy annealed at 893 K for 5 h, exhibiting fine grains with a {110} <001> orientation, shows excellent characteristics, such as an ultimate tensile strength of 832 MPa, magnetostriction of 117 ppm, and an output voltage density of 130 μV/mm3. The enhancement in power generation performance is due to the increase in magnetostriction, accompanying the refinement of crystal grains by recrystallization. The newly demonstrated linear relationship between grain size and magnetostriction (λs = 80.0 D−1/2 + 133) in this study can be a useful design guideline for further improvement in magnetostrictive materials.

Magnetostrictive tactile sensor array for force and stiffness detection

The sense of touch, also known as tactile perception, enables enhanced ambient environment awareness for modern robots. Fe-Ga alloys have demonstrated great potential in tactile sensor applications due to their significant inverse magnetostrictive effect. This study first develops a magnetostrictive sensor unit, consisting of permanent magnets, Fe-Ga wires, and Hall sensors to detect static and dynamic forces, as well as sample stiffness. Numerical models for individual sensor units are derived for force and stiffness detection, respectively. The force measurement range of tactile sensor unit is 0 to 3 N, and the sensitivity is 126 mV/N. A tactile sensor array is then developed and validated on a commercial robotic hand. Parametric studies investigating sensor interference and sensor arrangement are completed using finite element modeling. The tactile sensor array is able to detect stiffness of both monolithic and composite samples with a measurement error less than 8.3%. The magnetostrictive tactile sensor array developed in this study can facilitate precise grasping and intelligent control for future robots.

Villari Effect at Low Strain in Magnetoactive Materials.

Magnetic composites of soft magnetic FeGa particles embedded in a silicone matrix have been synthesized. The Villari effect has been studied depending on the size and concentration of the particles and on the magnetic state of the composite. The results indicate a decrease in the Villari effect when the concentration of the magnetic particles increases. These results suggest a relationship between the Villari effect and the mechanical properties of the composites. The Young’s modulus of the composites has been obtained by microindentation and their values related to the intensity and slope of the Villari signals. The results are explained on the basis that the reduction in the cross section of the composite when submitted to stress is the main origin of the variation of the magnetic flux in the Villari effect in this kind of composite. It has also been obtained that the magnetic state of the composite plays an important role in the Villari signal. When the magnetization of the composite is greater, the magnetic flux across the composite is greater too and, so, the same reduction in the cross section originates a greater Villari signal.

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.

Magnetocaloric Effect, Magnetoresistance of Sc0.28Ti0.72Fe2, and Phase Diagrams of Sc0.28Ti0.72Fe2−xTx Alloys with T = Mn or Co

(Sc,Ti)Fe2 Laves phases present a relatively unique case of first-order ferro-ferromagnetic transition originating from an instability of the Fe moment. In addition to large magnetoelastic effects making them potential negative thermal expansion materials, here, we show that Sc0.28Ti0.72Fe2 and related alloys also present sizable magnetocaloric and magnetoresistance effects. Both effects are found substantially larger at the ferro-ferromagnetic transition (Tt1) than near the Curie temperature TC, yet they remain limited in comparison to other classes of giant magnetocaloric materials. We suggest a strategy to improve these properties by bringing the transition at Tt1 close to TC, and test its possible realization by Co or Mn for Fe substitutions. The structural and magnetic phase diagrams of Sc0.28Ti0.72Fe2−xTx alloys with T = Mn or Co are explored. Substitutions for Fe by adjacent Mn or Co elements give rise to a breakdown of the long-range ferromagnetic order, as well as a swift disappearance of finite moment magnetism.

Strongly Correlated Molecular Magnet with Curie Temperature above 60 K

Summary Two-dimensional crystals with ferromagnetic ordering would lead to unprecedented possibilities for magnetic, magneto-optic, and magnetoelectric applications. However, long-range ferromagnetic ordering in two-dimensional van der Waals materials is strongly diminished by thermal fluctuation, while three-dimensional systems show the stiffness of magnetic ordering temperature to magnetic fields. Here, we report the discovery of intrinsic ferromagnetic ordering temperature of 60 K in an iron/tetracyanoquinodimethane layer via superconducting precursor. In such a molecular ferromagnet, an unprecedented control of ferromagnetic fluctuation temperature by ∼200% improvement is realized through magnetic fields. We demonstrate magnetodielectric coupling with a concomitant transition in magnetic ordering. A small magnetic field of 0.01 T enables an effective route to realize a sizable transition shift in magnetodielectric states. Stimulated by photoirradiation, it manifests a hidden metallic conducting state, declaring a metallic ferromagnet. The molecular ferromagnet and photoirradiation-induced hidden metallic phase present a “holy grail” in the field of molecular conducting magnets.

Extended x-ray absorption fine structure spectroscopy of stretched magnetic films on flexible substrate

This study investigates element-specific atomic distances and strains in ferromagnetic (FM) nano-thin films deposited on a flexible substrate, which can be modulated by stretching the substrate. Extended x-ray absorption fine structure (EXAFS) spectroscopy was used for the experiments. Both in-plane tensile and out-of-plane compressive strains were investigated by applying %-order tensile strains to the substrate. The atomic distance changes induced by stretching the substrate were quantitatively discussed by considering the Poisson compression, crystalline orientations of the FM metals, and polarization in the EXAFS measurement. Consequently, the ratio of strain transfer from the flexible substrate to the FM layers was estimated to be about 30% and 60% in Co and Fe nano-thin films, respectively. The strain transfer in Co films with different Co or Pt underlayer thicknesses was also measured. The results are compared with the thickness dependence of the effective magnetoelastic coupling constant, which represents the magnitude of the inverse magnetostriction effect. Although the strain transfer partially contributes to the thickness dependence, the difference in the Co lattice constant is suggested to have a significant influence on the effective magnetoelastic coupling constant.

Magnetic Properties of Tetragonal Cobalt Manganese Ferrite Particles Prepared Using the Molten Salt Method

Both magnetization and magnetic anisotropy of CoMn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> particles composed of the Jahn-Teller (JT) Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions with an expected large magnetoelastic effect were investigated. CoMn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> particles were prepared by using a molten salt method with KBr as a fluxing agent. A tetragonally distorted spinel structure was confirmed for x = 1.3 or higher. This suggests that an increase in Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions causes JT distortion of c/a > 1. However, Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> doping causes spin canting and decreased magnetization. A large saturation magnetization of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> = 44 emu/g and high coercivity of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> = 4300 Oe were observed for the sample with x = 1.4 at 10 K. In addition, the magnetic anisotropy field, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> , and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> increased with the increasing x from x = 1.3, where JT distortion was first observed.

Large magnetic anisotropy in highly strained epitaxial MgFe2O4 thin films

In order to acquire a soft magnetic film with low conductivity and large magnetic anisotropy, the strain-modulated magnetic anisotropy is studied in epitaxial MgFe2O4 (MFO) films. The MFO films with thicknesses of 25, 48, 75, and 110 nm are grown on the MgAl2O4 (MAO) (100) substrate using a pulsed laser deposition technique. Due to the large lattice-mismatch (3.34%) between MFO and MAO substrates, the interface exhibits a large tetragonal compressive strain. The results of field-dependent magnetization suggest the soft magnetic nature of all the measured MFO films. The analysis of angular dependent ferromagnetic resonance reveals the large uniaxial magnetic anisotropy energy (Ku) of −1.62 × 106 erg/cm3 in the highly strained 25 nm film, and Ku decreases with the increasing thickness due to strain relaxation. The observed large magnetic anisotropy in these highly strained MFO thin films is larger than most of the soft ferrite thin films, which arise due to tetragonal distortion and inverse magnetostriction. The epitaxial MFO thin films with enhanced magnetic anisotropy could be one of the potential candidates for spin filters.

Effect of compressive mechanical stress on the magnetic properties of LiTiZn ferrite ceramics

In the article, it was experimentally determined that compressive mechanical stress affects the parameters of the temperature dependence of the initial permeability. LiTiZn ferrite ceramics were sintered at 1010 °C for 2 h in air. The experimental curves were mathematically processed using the phenomenological expression to describe the initial magnetic permeability according to the Smith-Wijn model. It is shown that the change in the shape of the experimental curves correlates with the calculated data of the increase in the demagnetizing factor with an increase in mechanical stress. It is hypothesized that the change in the shape of the temperature curves is due to the magnetoelastic effect and the temperature dependence of the magnetostriction constant. Also, it was found that mechanical stress does not affect the X-ray microstructural parameters, including the true physical broadening of the reflexes. At the same time, the growth of mechanical stress to the maximum possible level for such type of ferrite ceramics leads to an increase in the coercive force by 10%. The character of the impact of mechanical stress on the shape of the temperature dependence curve of the initial permeability differs from the effect of non-magnetic Al2O3 additives. Thus the character of the change in the shape of the temperature dependence curve of the initial permeability allows monitoring nonmagnetic phases or mechanical stress in a LiTiZn ferrite ceramics production.

Flexible Magnetostrictive Nanocellulose Membranes for Actuation, Sensing, and Energy Harvesting Applications

Magnetostrictive composite known as magnetostrictive nanocellulose membrances (MNMs) were fabricated by embedding Terfeonol-D particles into cellulose nanofibers (CNF). MNMs inherit flexibility and biodegradability from CNF while exhibiting magnetomechanical responses; as such, the valuable rare-earth (Terfenol-D) particles can be recycled. Various orientations of the Terfenol-D particles were induced in the MNMs, and those with in-plane alignment showed the strongest magnetostrictive effect but the lowest Villari effect. Materials with such a unique combination of properties dovetail nicely with Internet of Things that require ubiquitous sensing, actuation and energy harvesting in one package.

Study of Induced Magnetic Anisotropy by Lattice Distortion in Cobalt Ferrite Thin Film Grown on (Mg,Sn)3O4 Buffer Layers

We have investigated structural and magnetic properties of cobalt ferrite (CFO)(001) epitaxial thin films grown by RF magnetron sputtering method on (Mg,Sn) 3 O 4 (MSO) buffer layers to induce large perpendicular magnetic anisotropy (PMA) through the magneto-elastic effect. Tuning of the CFO distortion was demonstrated by changing the film thickness of CFO. Torque measurements revealed that a 5-nm thick CFO thin film showed the PMA constant K u = 25.8±1.3 Merg/cm 3 at room temperature, which is extraordinarily large for a ferromagnetic oxide.

Deterministic magnetic domain wall motion induced by pulsed anisotropy energy

We propose a method to induce deterministic motion of a magnetic domain wall in a nanowire by inducing short strain pulses uniformly along the nanowire. Via inverse magnetostriction, a strain pulse causes the magnetic anisotropy to vary uniformly on a timescale comparable to the magnetisation dynamics. The resultant torque on the magnetic moments within the domain wall cause it to move along the nanowire. Using numerical calculations we analyse in detail the dependence of the domain wall’s motion on the material’s parameters and on the anisotropy pulse profile, and we consider the specific case of the anisotropy induced by voltage pulses applied to a hybrid piezoelectric/ferromagnet device. The method will be applicable to a range of magnetic textures including skyrmions, solitons, and domain walls in antiferromagnets, and is prospective for applications in a range of areas including ultra-energy efficient information storage and processing, communications technologies, position encoding and biomedical science.

Analysis and Modeling of a passive force sensor based on Villari effect

The paper deals with an engineering application of the inverse magnetostrictive Villari effect. This effect is usually modeled through multi-variate relationships, strongly non linear and with hysteresis. Here, the task is to provide a suitable formulation of those relationships aiming at a device able to measure mechanical force profiles with good accuracy. The device is analyzed and modeled by a mapping function, resulting in an algorithm that reconstructs the time profile of the applied force. A preliminary calibration characterization is carried out on a concept device that exploits Galfenol as magnetostrictive material. Finally, some tests performed with the aim of validating the algorithm and to estimate its performance are presented.

Strain-mediated propagation of magnetic domain-walls in cubic magnetostrictive materials

The role played by magnetoelastic effects on the properties exhibited by magnetic domain walls propagating along the major axis of a thin magnetostrictive nanostrip, coupled mechanically with a thick piezoelectric actuator, is theoretically investigated. The magnetostrictive layer is assumed to be a linear elastic material belonging to the cubic crystal classes $$\bar{4}$$3m, 432 and m$$\bar{3}$$m and to undergo isochoric magnetostrictive deformations. The analysis is carried out in the framework of the extended Landau–Lifshitz–Gilbert equation, which allows to describe, at the mesoscale, the spatio-temporal evolution of the local magnetization vector driven by magnetic fields and electric currents, in the presence of magnetoelastic and magnetocrystalline anisotropy fields. Through the traveling-wave transformation, the explicit expression of the key features involved in both steady and precessional regimes is provided and a qualitative comparison with data from the literature is also presented.