Strong Magnetostriction Research Articles

Magneto-mechanically derived diffusion processes in ultra-soft biological hydrogels

Magneto-active hydrogels (MAHs) consist of a polymeric network doped with magnetic particles that enable the material to mechanically respond to magnetic stimuli. This multifunctionality allows for modulation of mechanical properties in a remote and dynamic manner. These characteristics combined with the biocompatibility of hydrogels, make MAHs excellent for drug delivery and biological scaffolds. In this work, ultra-soft biological MAHs with strong magnetostriction are fabricated from human blood plasma (∼20 Pa). The material is experimentally tested using a novel in-house device that allows for a precise control of magnetic actuation conditions, enabling the hydrogel modulation in terms of mechanical deformation and stiffness. We study the impact of magnetic actuation on the solvent expulsion and diffusion dynamics within the polymeric network. To further elucidate the mechanisms driving solvent diffusion processes, a computational framework for modeling the diffusion process of two different species within a magneto-responsive material is proposed. These experimental and computational outcomes open exciting new opportunities for the use of ultra-soft MAHs in bioengineering applications.

Coherent Oscillations in a SrRuO3/BiFeO3 Superlattice.

We investigated the ultrafast dynamics of a SrRuO3/BiFeO3 superlattice grown on a SrTiO3 substrate using a near infrared pump-probe technique at various temperatures. The superlattice exhibits a ferromagnetic order inherited from the SrRuO3 layer. The pump-induced changes in the reflectivity reveal periodic oscillations. We found that the oscillation frequency can be well explained by zone-folded acoustic phonon oscillations, whose dispersion depends on the sound velocity, density, and thickness within the supercell of each constituent layer. It is found that the observed oscillation frequency corresponds to the A1 mode, which suggests that oscillations are excited due to pump-induced expansion of the SrRuO3 layer that absorbs the pump photon. Temperature-dependent measurements reveal significant suppression of the oscillation amplitude in the ferromagnetic state. The suppressed amplitude is proportional to the square of the magnetization, M(T)2. This phenomenon can be attributed to a strong magnetostriction effect of SrRuO3 that suppresses lattice expansion upon pumping.

Effect of magnetic fields on the formation of the neck of a flat aluminum sample with inclusions during stretching

The present study investigates the effect of a constant magnetic field (MF) on the destruction of an aluminum alloy containing ferromagnetic inclusions in the creep regime. The authors found that preliminary exposure (before mechanical load P = 150 … 160 N) of aluminum alloy to a constant MF (with induction B up to 0.7 T and exposure time of at least 30 min) increases the alloy creep (up to 20%) and changes the nature of the formation of a zone of intense plastic deformation (“neck”). The authors associate the observed changes with an increasing role of internal mechanical stresses due to the strong magnetostriction of inclusions.

Interplay of spin, phonon, and lattice degrees in a hole-doped double perovskite: Observation of spin–phonon coupling and magnetostriction effect

Unlike a typical spin–phonon coupling, an exhibition of unconventional spin–phonon coupling, which is mediated via magnetostriction effect, is reported in a hole-doped double perovskite Pr1.5Sr0.5CoMnO6. Various investigations including electronic and crystal structures, spin structure, transport property, lattice dynamics, and theoretical density of states analysis by density-functional theory (DFT) have been performed. A substantial increase in the mean oxidation states of Co ions and a concurrent abrupt decrease in the resistivity upon Sr doping is observed, thus altering its underlying transport mechanism. An insulating and ferromagnetic (FM) ground state is predicted by DFT calculations. The neutron diffraction data analysis reveals a complex crystal structure of Pr1.5Sr0.5CoMnO6, which consists of B-site disordered monoclinic (P21/n) and orthorhombic (Pnma) structures, highlighting the presence of an anti-site disorder in the system. The analysis also suggests an overall FM ordering of Co/Mn spins below 150 K for the monoclinic phase, whereas no such magnetic ordering is found for the orthorhombic phase. More interestingly, the neutron powder diffraction study perceives the presence of a strong magnetostriction effect in the system. Raman spectroscopy unravels the presence of a spin–phonon coupling, which is essentially mediated by the magnetostriction effect.

Spin-induced strongly correlated magnetodielectricity, magnetostriction effect, and spin-phonon coupling in helical magnet Fe3(PO4)O3

Helical magnets are extremely promising, as they have fascinating magnetic, electric, and phononic properties. Here, we report a spectrum of simultaneously occurring and highly entangled intriguing phenomena induced by helical spin ordering in a noncentrosymmetric and spin-frustrated system ${\mathrm{Fe}}_{3}(\mathrm{P}{\mathrm{O}}_{4}){\mathrm{O}}_{3}$. These phenomena include magnetodielectric effect in the form of a frequency-independent pronounced dielectric peak, clear magnetostriction effect manifested as a dramatic downturn in the thermal variation of lattice parameters, and strong spin-phonon coupling (which displays a unique anomalous hardening and softening of various phonon modes) at temperatures as high as ${T}_{N}=163\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The observed dielectric peak is seemingly associated with a structural distortion via the strong magnetostriction effect.

Nanomechanical probing and strain tuning of the Curie temperature in suspended Cr2Ge2Te6-based heterostructures

Two-dimensional magnetic materials with strong magnetostriction are attractive systems for realizing strain-tuning of the magnetization in spintronic and nanomagnetic devices. This requires an understanding of the magneto-mechanical coupling in these materials. In this work, we suspend thin Cr2Ge2Te6 layers and their heterostructures, creating ferromagnetic nanomechanical membrane resonators. We probe their mechanical and magnetic properties as a function of temperature and strain by observing magneto-elastic signatures in the temperature-dependent resonance frequency near the Curie temperature, TC. We compensate for the negative thermal expansion coefficient of Cr2Ge2Te6 by fabricating heterostructures with thin layers of WSe2 and antiferromagnetic FePS3, which have positive thermal expansion coefficients. Thus we demonstrate the possibility of probing multiple magnetic phase transitions in a single heterostructure. Finally, we demonstrate a strain-induced enhancement of TC in a suspended Cr2Ge2Te6-based heterostructure by 2.5 ± 0.6 K by applying a strain of 0.026% via electrostatic force.

Fully reversible magnetoelectric voltage controlled THz polarization rotation in magnetostrictive spintronic emitters on PMN-PT

THz polarization control upon generation is a crucially missing functionality. THz spintronic emitters based on the inverse spin Hall effect (ISHE) allow for this by the strict implicit orthogonality between their magnetization state and the emitted polarization. This control was until now only demonstrated using cumbersome external magnetic field biasing to impose a polarization direction. We present here an efficient voltage control of the polarization state of terahertz spintronic emitters. Using a ferromagnetic spin pumping multilayer exhibiting simultaneously strong uniaxial magnetic anisotropy and magnetostriction in a crossed configuration, an emitter is achieved where, in principle, the stable magnetization direction can be fully and reversibly controlled over a 90° angle span only by an electric voltage. To achieve this, an engineered rare-earth based ferromagnetic multilayer is deposited on a piezoelectric (1−x)[Pb(Mg0.33Nb0.66)O3]−x[PbTiO3] (PMN-PT) substrate. We demonstrate experimentally a reversible 70° THz polarization rotation by sweeping the substrate voltage over 400 V. This demonstration allows for a fully THz polarization controlled ISHE spintronic terahertz emitter not needing any control of the magnetic bias.

Colossal crystalline anisotropic magnetoresistance in A-type antiferromagnetic film

A colossal crystalline anisotropic magnetoresistance (CAMR) is observed in an epitaxial A-type antiferromagnetic Pr0.5Sr0.5MnO3 (PSMO) thin film, which is 1600% at 20 K under the magnetic field of 50 kOe. This colossal CAMR is associated with an anisotropic switching process between low and high resistivity states. Based on the symmetry of angular dependence of the CAMR, we attribute the origin to the strong anisotropic magnetostriction in PSMO. Our results explored a potential utilization of an A-type antiferromagnetic thin film for CAMR based spintronic devices.

Understanding the importance of local magnetic moment in monolayer FeSe

Local magnetic moment (LMM) and antiferromagnetic (AFM) fluctuation play a critical role in affecting the properties of FeSe superconductor. By constraining the local magnetic moment on Fe atoms using density functional theory, we investigate how LMM in FeSe monolayer alters the total energy, heights of Se atoms, band structure, and the electronic properties, for three different AFM spin arrangements which consist of the checkerboard (CB), collinear (CL), and pair-checkerboard (PC) spin phases. We find that (i) the total energy decreases drastically in all three spin structures when LMM develops, showing that the existence of LMM significantly stabilizes the system. The optimal LMM is found to be 2.23, 2.54, and $2.47\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$, respectively, in the CB, CL, and PC spin phases. (ii) The heights of Se atoms increase markedly (and in a quadratic manner) with LMM, demonstrating a strong magnetostriction effect. Also intriguingly, we find that the Se heights are insensitive to spin ordering, displaying a rather universal dependence on LMM in three different AFM spin phases. (iii) LMM is shown to alter substantially the electron band structures and Fermi surfaces. Near their optimal LMM, while both CB and PC phases possess electron pockets and no hole pockets, the CL phase exhibits neither electron pockets nor hole pockets, and interestingly, it becomes a semiconductor of a small gap of 60 meV. These results reveal that there is a rich and interesting physics to be tuned by LMM in FeSe superconductor.

Spin orientation and strain tuning valley polarization with magneto-optic Kerr effects in ferrovalley VS2 monolayer

Recently, two-dimensional ferrovalley materials have attracted increasing interest due to their intrinsic ferromagnetism and valley polarization. The 2H VS2 monolayer is taken as an example, and our calculations indicate that the spin direction and strain can modify its valley splitting while further leading to a strong dependence of the Kerr signals. Moreover, the strain-tuned magnetocrystalline anisotropic energy and magnetostrictive coefficient provide a strong magnetostriction in the 2H VS2 monolayer. These results provide a theoretical reference for practical applications involving valley polarization and magneto-optic Kerr effects in 2D ferrovalley materials.

A Dynamic Magnetostriction Model of Grain-Oriented Sheet Steels Based on Becker–Döring Crystal Magnetization Model and Jiles–Atherton Theory of Magnetic Hysteresis

Grain-oriented (GO) sheet steels are widely used as the core material in large power transformers. The strong magnetostriction in GO sheet steels, however, causes undesirable vibrations and acoustic noises, and is difficult to estimate in the design optimization of power transformers. This article proposes a new magnetostriction model of GO sheet steels by combining the Becker-Doring crystal model and the dynamic Jiles-Atherton hysteresis model. Incorporated in the finite-element analysis (FEA), the new model can correctly simulate the butterfly loops of magnetostriction in GO sheet steels. The effectiveness and accuracy of the proposed model are verified by the experimental measurement results on a single sheet sample in a free state with no external stress.

Strain-magneto-optics in ferrite-spinel – new magneto-optical phenomena associated with magnetoelastic interactions

The correlation between magnetoreflection, magnetotransmission of unpolarized light in the infrared range and the magnetoelastic properties of magnetics is reported for the ferrimagnetic spinel CoFe2O4 single crystal. The new physical mechanism responsible for the spectral and field-dependent peculiarities of magnetoreflection and magnetotransmission in the ferrite-spinel possessing strong magnetostriction is discussed. The influence of a magnetic field on specular reflection and transmission spectrum is likely to be indirect: magnetic-field-induced strong strains and deformations of the crystal lattice lead to the change in the electron energy structure and, hence, optical properties of CoFe2O4. The revealed mechanism of new infrared magnetooptical effect in magnetostrictive magnetics paves the way towards new research area called as a strain-magneto-optics.

Single Goss grain growth by isothermal annealing in rolled Fe–Al–Ga–NbC sheets

The (Fe82Al13.5Ga4.5)99.9(NbC)0.1 sheets with strong Goss texture and large magnetostriction were prepared by rolling and isothermal annealing processes. Single Goss grain growth was observed in sheets undergoing isothermal annealing at 1050 °C for 1 h using Ar as protecting gas. With annealing time increasing to 8 h at 1050 °C, a largest magnetostriction of 154 × 10−6 is obtained in sheet and a large λ// (the maximum magnetostriction with magnetic field parallel to rolling direction) of 160 × 10−6 along the rolling direction is also observed. The fact that a λ// of 160 × 10−6 along RD can be achieved with only 4.5 at% Ga in the Fe-18 at% (Al, Ga) sheet is of practical importance. Compared with previous studies in Fe–Al and Fe–Ga sheets, this paper provides a more efficient approach to prepare strong Goss textured sheets. In this way, a slow continuous heating process, sulfur-induced surface energy control and high-temperature annealing above 1200 °C are no more necessary. It shows a good prospect for industrial production of high-performance magnetostrictive alloy sheets.

Structure and Phase Transformation in the Giant Magnetostriction Laves-Phase SmFe2.

As one class of the most important intermetallic compounds, the binary Laves-phase is well-known for its abundant magnetic properties. Samarium-iron alloy system SmFe2 is a prototypical Laves compound that shows strong negative magnetostriction but relatively weak magnetocrystalline anisotropy. SmFe2 has been identified as a cubic Fd3̅m structure at room temperature; however, the cubic symmetry, in principle, does not match the spontaneous magnetization along the [111]cubic direction. Here we studied the crystal structure of SmFe2 by high-resolution synchrotron X-ray powder diffraction, X-ray total scattering, and selected-area electron diffraction methods. SmFe2 is found to adopt a centrosymmetric trigonal R3̅m structure at room temperature, which transforms to an orthorhombic Imma structure at 200 K. This transition is in agreement with the changes of easy magnetization direction from [111]cubic to [110]cubic direction and is further evidenced by the inflection of thermal expansion behavior, the sharp decline of the magnetic susceptibility in the field-cooling-zero field-cooling curve, and the anomaly in the specific heat capacity measurement. The revised structure and phase transformation of SmFe2 could be useful to understand the magnetostriction and related physical properties of other RM2-type pseudocubic Laves-phase intermetallic compounds.

Breakdown of antiferromagnet order in polycrystalline NiFe/NiO bilayers probed with acoustic emission

Magnetization reversal of polycrystalline NiFe/NiO bilayers was investigated using magneto-optical indicator film imaging and acoustic emission techniques. Sporadic acoustic signals were detected in a constant magnetic field after the magnetization reversal. It is suggested that they are related to elastic waves excited by sharp shocks in the NiO layer with strong magnetostriction. Their probability depends on the history and number of repetitions of the field cycling, thus testifying the thermal-activation nature of the long-time relaxation of an antiferromagnetic order. These results provide evidence of spontaneous thermally activated switching of the antiferromagnetic order in NiO grains during magnetization reversal in ferromagnet/antiferromagnet (FM/AFM) heterostructures. The respective deformation modes are discussed in terms of the thermal fluctuation aftereffect in the Fulcomer and Charap model which predicts that irreversible breakdown of the original spin orientation can take place in some antiferromagnetic grains with disordered anisotropy axes during magnetization reversal of exchange-coupled FM/AFM structures. The spin reorientation in the saturated state may induce abrupt distortion of isolated metastable grains because of the NiO magnetostriction, leading to excitation of shock waves and formation of plate (or Lamb) waves.

Dynamics of electron density, spin-phonon coupling, and dielectric properties ofSmFeO3nanoparticles at the spin-reorientation temperature: Role of exchange striction

Samarium orthoferrite $(\mathrm{SmFe}{\mathrm{O}}_{3})$ has been the subject of debate on the existence or nonexistence of ferroelectric properties. It has a high spin-reorientation transition temperature ${T}_{\mathrm{SR}}$ (480 K). Detailed synchrotron x-ray diffraction and Raman spectroscopy dielectric investigations in the 300 to 600 K temperature range of $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles $(\ensuremath{\sim}65\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$ have been performed. Raman spectroscopy established the existence of strong spin-phonon coupling and magnetostriction in the system. Magnetic measurements showed a spin-reorientation transition region from 480 to 450 K similar to that of a single crystal. The dielectric constant confirmed a clear anomaly around ${T}_{\mathrm{SR}}$. The signature of unusual relaxor ferroelectric behavior in $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles from 380 to 480 K was observed in the dielectric properties. The electron density plots obtained using Rietveld refinement of the synchrotron x-ray diffraction data showed the displacement of the Sm and Fe ions, which can play a key role in the anomalous behavior at ${T}_{\mathrm{SR}}$. The analysis indicated the presence of magnetoelectric coupling due to the exchange interaction between Sm and Fe spins in $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles.

Strong anisotropy and magnetostriction in the two-dimensional Stoner ferromagnetFe3GeTe2

Computationally characterizing magnetic properies of novel two-dimensional (2D) materials serves as an important first step of exploring possible applications. Using density-functional theory, we show that single-layer ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ is a potential 2D material with sufficiently low formation energy to be synthesized by mechanical exfoliation from the bulk phase with a van der Waals layered structure. In addition, we calculated the phonon dispersion demonstrating that single-layer ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ is dynamically stable. Furthermore, we find that similar to the bulk phase, 2D ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ exhibits a magnetic moment that originates from a Stoner instability. In contrast to other 2D materials, we find that single-layer ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ exhibits a significant uniaxial magnetocrystalline anisotropy energy of $920\ensuremath{\mu}\mathrm{eV}$ per Fe atom originating from spin-orbit coupling. Finally, we show that applying biaxial tensile strains enhances the anisotropy energy, which reveals strong magnetostriction in single-layer ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ with a sizable magneostrictive coefficient. Our results indicate that single-layer ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ is potentially useful for magnetic storage applications.

BaFe(2)Se(3) a high T(C) magnetic multiferroic with large ferrielectric polarization.

The iron selenides are important because of their superconducting properties. Here, an unexpected phenomenon is predicted to occur in an iron-selenide compound with a quasi-one-dimensional ladder geometry: BaFe(2)Se(3) should be a magnetic ferrielectric system, driven by its magnetic block order via exchange striction. A robust performance (high T(C) and large polarization) is expected. Different from most multiferroics, BaFe(2)Se(3) is ferrielectric, with a polarization that mostly cancels between ladders. However, its strong magnetostriction still produces a net polarization that is large (∼0.1 μC/cm(2)) as compared with most magnetic multiferroics. Its fully ferroelectric state, with energy only slightly higher than the ferrielectric, has a giant improper polarization ∼2-3 μC/cm(2).

Understanding strong magnetostriction in Fe100−xGax alloys

Magnetostriction of ferromagnetic materials describes the change of their shape or dimension in response to the reorientation of magnetization under the influence of external magnetic field. Fe100−xGax binary alloys (Galfenol) have large magnetostriction and excellent ductility; and they are very promising rare-earth free materials for applications in sensors, actuators, energy-harvesters and spintronic devices. Here we report results of large-scale ab initio molecular dynamics (AIMD) simulations for Galfenol, especially regarding the mechanism that leads to the sudden drop of tetragonal magnetostriction at x ~ 19, a long-standing puzzle for the community. Based on rigid band analysis, we propose possible ways to further optimize the performance of Galfenol for device applications. For example, we found that the substitution of a small amount of Cu for Ga (1.6%) in certain configuration may double the magnetostriction of Galfenol.

Magnetostriction of the polycrystalline Fe80Al20 alloy doped with boron

The doping of Fe80Al20 polycrystalline alloy with 2% of boron increased the total magnetostriction twofold compared to a sample without boron. A value close to 80ppm was achieved at 300K. The microstructures of the boron-doped alloys show a dendritically solidified matrix with interdendritic α-FeAl and/or Fe3Al and Fe2B eutectic between the grains. The XRD analysis reveals an increase in the volume fraction of α-FeAl and a correspondent decrease of the Fe3Al phase volume fraction as the boron content increases. The increase of the volume fraction of this tetragonal Fe2B phase in the samples doped with boron causes the decrease of the strong volume magnetostriction that was observed in the alloy without boron. There is some evidence that the improvement of the magnetostriction magnitude due to the addition of boron to the Fe80Al20 alloy could reach the maximal magnetostriction if the 1:1 optimal ratio of the volume fractions of the α-FeAl and Fe3Al phases could be reached.