Magnetoelastic Interaction Research Articles

Stress-dependent Magnetization Processes in Co based Amorphous Microwires

Soft magnetic materials with high magnetic susceptibility are sensitive to changing magnetic fields and generate electrical voltage signals whose spectra contain higher harmonics. Magnetic susceptibility and saturation field are largely determined by magnetoelastic interactions in amorphous ferromagnets, respectively, the amplitudes of higher harmonics should depend on external mechanical stresses. In this work, we study the processes of magnetization reversal in amorphous microwires of two compositions: Co71Fe5B11Si10Cr3 and Co66.6Fe4.28B11.51Si14.48Ni1.44Mo1.69 under the action of external tensile stresses. For the first composition, mechanical stresses exceeding a certain limit (more than 350 MPa) lead to the transformation of the magnetic hysteresis from a bistable type to an inclined one. In this case, a sharp change of the harmonic spectrum is observed. In microwires of the second composition with an initially inclined loop, external stresses cause a monotonous increase in the slope of the hysteresis loop (a decrease in susceptibility). In this case, the amplitudes of higher harmonics change significantly at low stresses, less than 100 MPa. The results were obtained by remagnetization of microwire samples using a system of flat coils, which demonstrates the potential of using these materials as wireless sensors of mechanical stresses with remote reading.

Nonreciprocity of surface acoustic waves coupled to spin waves in a ferromagnetic bilayer with noncollinear layer magnetizations

Nonreciprocity of propagation of surface acoustic waves (SAWs) in the microwave frequency band can be achieved using the magnetoelastic interaction of SAWs with spin waves (SWs) propagating in magnetic heterostructures. Recent works have shown that the ultimate isolation of a counterpropagating hybridized SAW/SW is achieved in heterostructures consisting of a synthetic antiferromagnet—a ferromagnetic (FM) bilayer with antiferromagnetic Ruderman-Kittel-Kasuya-Yosida interlayer coupling—placed on top of a piezoelectric acoustic waveguide. In this work, we study in detail a more practical and technologically simpler system based on an FM bilayer, where layers are coupled by only dipole-dipole interaction, and having noncollinear magnetizations of the FM layers. A weak in-plane anisotropy with noncollinear easy axes in the layers is shown to be the only essential factor for the realization of strongly nonreciprocal propagation of a hybridized SAW/SW. We formulate requirements for the relative orientation of the layer’s magnetizations and wave propagation direction necessary to realize an efficient SAW isolator, and demonstrate examples of SAW transmission characteristics which prove the possibility of achieving an isolation exceeding 50 dB for a submillimeter-long FM bilayer with insertion losses of just a few decibels more than those of a pure SAW device. In addition to relative fabrication simplicity, the proposed magnetoelastic heterostructure exhibits a reasonable robustness in respect to deviations in the anisotropy axes and/or bias field directions—an important benefit for device mass production. Published by the American Physical Society 2024

A Novel High Entropy FeCoNi(GaCu)1.0 Alloy with Attractive Soft Magnetic Properties.

The new FeCoNi(GaCu)1.0 alloy has interesting soft magnetic properties at room temperature compared to other high entropy magnetic alloys (HEMAs). It is a single-phase material with high saturation magnetization Ms = 114 Am2⋅kg-1, high relative magnetic permeability 1675, and low coercive field 320 A⋅m-1. In addition, it presents a TC = 591 °C. The spin wave stiffness is D = 85.21 meV Å2. This value is 3 times smaller than in pure Fe, thus exchange interaction among Fe, Co, and Ni atoms is smaller than those between Fe-Fe atoms, causing TC to decrease. The saturation magnetostriction λs is 5.7×10-6 and is as small as others λs values also found in other based FeCoNi HEMAs. Those small λs may be caused by the diffuse distortions of the lattice, a known effect on HEAs, which may be interfering in the magnetoelastic interaction between μ and the lattice.

Investigation of phonons and magnons in [Ni80Fe20/Au/Co/Au] N multilayers

The interaction between phonons and magnons is a rapidly developing area of research, particularly in the field of acoustic spintronics. To discuss this interaction, it is necessary to observe two different waves (acoustic and spin waves) with the same frequency and wavelength. In the Ni80Fe20/Au/Co/Au system deposited on a silicon substrate, we observe the interaction between spin waves and surface acoustic waves using Brillouin light scattering spectroscopy. As a result, we can selectively control (activate or deactivate) the magnetoelastic interaction between the fundamental spin wave mode and surface acoustic waves. This is achieved by adjusting the magnetostrictive layer thickness in the multilayer. We demonstrate that by adjusting the number of layers in a multilayer structure, it is possible to precisely control the dispersion of surface acoustic waves while having minimal impact on the fundamental spin wave mode.

Photoinduced Nonthermal Reduction of the Coercive Field in FePt and FePt0.84Rh0.16 Epitaxial Thin Films in the L10 Phase

The time-resolved magneto-optical Kerr effect in epitaxial thin films of the FePt compound and the FePt0.84Rh0.16solid solution with the perpendicular magnetic anisotropy on MgO (001) substrates has been studied. The evolution of hysteresis loops at short (100 fs–1 ns) and long (1–20 ms) time scales after the excitation by a femtosecond light pulse has been studied. Long-lived nonthermal reduction of the coercive field has been detected. The coercive field is recovered in several milliseconds. It has been proposed to explain the observed phenomenon by the excitation of high-Q-factor acoustic resonances in the substrate/film system and to the strong magnetoelastic interaction in FePt and FePt0.84Rh0.16films.

Вторичный магнитоупругий резонанс в структуре: тонкая магнитная пленка – толстая упругая подложка

The task about excitation of connected magnetic and elastic vibrations in flat-parallel structure consisted of normal magnetized thin magnetic film applied on thick nonmagnetic substrate is considered. As a result of estimated task solution the amplitude-frequency characteristics of magnetic and elastic vibrations are found. It is shown that in conditions when the ferromagnetic resonance frequency is higher then own elastic vibration of the structure on the amplitude-frequency characteristics of magnetic vibrations applied the equidistance net of elastic resonances of structure. For the interpretation of observed resonance net it is proposed the model of phase synchronization between initial excitation and elastic wave which experience two passages along the thickness of structure. It is shown that the frequency of maximum elastic vibrations rounding exceeds frequency of maximum magnetization characteristic. The existence of own rounding elastic vibrations characteristic is named the second elastic system resonance. It is investigated the dependence of maximum second resonance characteristic from value of magnetoelastic interaction constant. It is shown that by increasing of this constant the frequency distance between both characteristic maxima increases. As a hypothesis of this increasing it is proposed the analogy with splitting of amplitude-frequency characteristic of system consisted of two connected resonators. It is investigated the amplitude-frequency characteristics magnetic and elastic vibrations in wide frequency region. On the equidistance elastic resonances net amplitude-frequency characteristic it is found the narrow equidistance disposed resonance depressions which are correspond to decreasing of amplitude more then two orders of value. It is shown that the frequency interval between neighbouring depressions is back proportional to distance between point of elastic vibrations registration and surface of substrate opposite to magnetic film. For the interpretation of depressions formation it is proposed the model which takes into account the phase opposition in registration point between wave which goes out of the excitation point and wave which is reflected from the opposite end of structure. Briefly noted some physical analogies of investigated phenomena.

Modelling domain-wall orientation in antiferromagnets driven by magnetoelastic interactions and volume variations

Modelling domain-wall orientation in antiferromagnets driven by magnetoelastic interactions and volume variations

Generation of imprinted strain gradients for spintronics

In this work, we propose and evaluate an inexpensive and CMOS-compatible method to locally apply strain on a Si/SiOx substrate. Due to high growth temperatures and different thermal expansion coefficients, a SiN passivation layer exerts a compressive stress when deposited on a commercial silicon wafer. Removing selected areas of the passivation layer alters the strain on the micrometer range, leading to changes in the local magnetic anisotropy of a magnetic material through magnetoelastic interactions. Using Kerr microscopy, we experimentally demonstrate how the magnetoelastic energy landscape, created by a pair of openings, enables in a magnetic nanowire the creation of pinning sites for in-plane vortex walls that propagate in a magnetic racetrack. We report substantial pinning fields up to 15 mT for device-relevant ferromagnetic materials with positive magnetostriction. We support our experimental results with finite element simulations for the induced strain, micromagnetic simulations, and 1D model calculations using the realistic strain profile to identify the depinning mechanism. All the observations above are due to the magnetoelastic energy contribution in the system, which creates local energy minima for the domain wall at the desired location. By controlling domain walls with strain, we realize the prototype of a true power-on magnetic sensor that can measure discrete magnetic fields or Oersted currents. This utilizes a technology that does not require piezoelectric substrates or high-resolution lithography, thus enabling wafer-level production.

Photoinduced Nonthermal Reduction of the Coercive Field in FePt and FePt0.84Rh0.16 Epitaxial Thin Films in the L10 Phase

The time-resolved magneto-optical Kerr effect in epitaxial thin films of the FePt compound and the FePt0.84Rh0.16 solid solution with the perpendicular magnetic anisotropy on MgO (001) substrates has been studied. The evolution of hysteresis loops at short (100 fs–1 ns) and long (1–20 ms) time scales after the excitation by a femtosecond light pulse has been studied. Long-lived nonthermal reduction of the coercive field has been detected. The coercive field is recovered in several milliseconds. It has been proposed to explain the observed phenomenon by the excitation of high-Q-factor acoustic resonances in the substrate/film system and to the strong magnetoelastic interaction in FePt and FePt0.84Rh0.16 films.

Thermal and magnetic properties of Fe7Se8 studied on single crystals

Specific heat, thermal expansion and magnetic measurements on single crystalline samples have been employed to study the interplay between the lattice and the magnetic state in the layered iron selenide compound Fe7Se8, which exhibits a ferrimagnetic order below TN ≈ 440 K and a spin reorientation transition upon cooling below Tsr ∼ 115 K. Thermal expansion measurements performed on single-crystal samples revealed significant anisotropic deformations of the crystal lattice with decreasing temperature below TN, an increase in the c/a ratio, and negative volume spontaneous magnetostriction (ωs ∼ −5.3⋅10−3 at 120 K). The first-order spin reorientation transition in Fe7Se8 is found to be accompanied by a hysteretic behavior of the specific heat and thermal expansion, and an anomaly in the ωs vs T dependence. The results obtained are indicative of a strong influence of the magnetoelastic interactions on the properties of Fe7Se8.

Phononic Crystal Cavity Magnomechanics

Phononic crystal (PnC) enables strong confinement of phonons in a wavelength-scale tiny area due to a band gap, which can enhance the interaction with different physical systems. Here, we utilize the PnC to demonstrate local manipulations of magnons by using ultrahigh frequency phonons confined in a phononic cavity, where the tiny and low-loss vibrations excite magnons in a micromagnet via magnetostriction. Moreover, we find that the magnetoelastic interaction is modulated by selectively exciting the cavity resonant modes. The results open up a realm of PnC cavity magnomechanics and will provide universal controls of ultrahigh frequency magnons and phonons with PnC circuits.

Controllable Fano-type optical response and four-wave mixing via magnetoelastic coupling in an opto-magnomechanical system

We analytically investigate the Fano-type optical response and the four-wave mixing (FWM) process by exploiting the magnetoelasticity of a ferromagnetic material. The deformation of the ferromagnetic material plays the role of mechanical displacement, which is simultaneously coupled to both optical and magnon modes. We report that the magnetostrictively induced displacement leads to realization of Fano profiles in the output field and is effectively well-tuned through adjusting the system parameters, such as effective magnomechanical coupling, magnon detuning, and cavity detuning. It is found that the magnetoelastic interaction also gives rise to the FWM phenomenon. The number of the FWM signals mainly depends upon the effective magnomechanical coupling and the magnon detuning. Moreover, the FWM spectrum exhibits suppressive behavior upon increasing (decreasing) the magnon (cavity) decay rate. The present scheme will open new perspectives in highly sensitive detection and quantum information processing.

Motion of a magnetic skyrmionium driven by acoustic wave

A magnetic skyrmionium does not exhibit skyrmion Hall effect due to its special structure with zero topological charge, which has an advantage over a skyrmion in the application of tracetrack memory. With the development of straintronics, acoustic waves could remotely control the topological magnetic structures, including skyrmionium. In this work, the acoustic wave induced dynamics of a skyrmionium on a strip film is studied by means of micromagnetic simulations. The results show that the motion of a skyrmionium is significantly influenced by the magnetic damping, the amplitude, and the frequency of the acoustic wave. The skyrmionium tends to acquire higher velocity at larger amplitude of the acoustic wave and smaller magnetic damping. With the increase in the acoustic wave amplitude, the skyrmionium deforms and moves faster due to stronger magnetoelastic interaction. When the frequency increases from 1 to 15 GHz, the velocity of skyrmionium generally increases except for the velocity fluctuation caused by magnetization resonance at a few frequencies. This work suggests a mechanical way to drive the motion of magnetic skyrmioniums by acoustic waves, offering potential applications in future information memory devices.

On the magnetic-structure origin of giant magnetostrictive effect in MnCoSi-based metallic helimagnets

Giant magnetostrictive effect, the huge volume and/or shape change of a material under an external magnetic field, is recently discovered in helimagnets with large magnetoelastic interactions. Here we revisit this effect in MnCoSi, a helical metamagnet with a unique Lifshitz tricritical point. By introducing minimal amount of Ni, the modified competing exchange interaction simultaneously lowers the tricritical temperature and even critical field of metamagnetism, leading to a giant, reversible, low-field magnetostrictive effect at ambient temperature. When applying a cyclic low field of 0.5 T, a giant reversible magnetostriction of 550 ppm can be achieved and maintained at 300 K. Interestingly, by advanced 3D-vector magnetic field measurement, a strong relation is found between magnetocrystalline anisotropy and the critical field of magnetostrictive effect. In-situ neutron powder diffraction results further reveal that the incommensurate helical antiferromagnetic structure with moment lying in ab plane transits into a ferromagnetic structure along b axis with increasing magnetic fields. During this metamagnetic transition, dramatical spin rotation triggers sharp anisotropic lattice change via strong magnetoelastic coupling, resulting in giant magnetostrictive effect. The saturated magnetostriction value is closely related with the amplitude of spin rotations. These findings not only design of a potential MnCoSi-based magnetostrictive material but also uncover the specific evolution of magnetic structures in the metamagnetic transition and the possible mechanism behind the macroscopic size change.

Fathoming the anisotropic magnetoelasticity and magnetocaloric effect in GdNi

Intermetallic GdNi adopts a CrB type of crystal structure (space group $Cmcm$), and it orders ferromagnetically via a second-order phase transition at 70 K, exhibiting unusually strong spontaneous striction along the three independent crystallographic axes in the ferromagnetically ordered state. We introduce a microscopic model to describe anisotropic changes of lattice parameters and elastic contribution to magnetocaloric effect of GdNi. In the model, results of density functional theory (DFT) calculations are used as inputs into a Hamiltonian that includes elastic energy of an anisotropic crystal lattice, exchange interactions, and Zeeman effect. The magnetic and elastic Hamiltonians are coupled through an anisotropic Bean-Rodbell model of magnetoelastic interactions. This coupling gives rise to anisotropic changes in the lattice parameters observed experimentally, and the model reveals good to reasonable agreements between the current theoretical results and earlier experimental data, thus validating the model within the limits of assumptions made. We also show that DFT calculations with $4f$ electrons of Gd treated as core electrons lead to a more adequate estimate of elastic constants of GdNi in comparison with the $\mathrm{LDA}+U$ method where $4f$ electrons are treated as valence electrons.

Resonant phonon-magnon interactions in freestanding metal-ferromagnet multilayer structures

We analyze resonant magneto-elastic interactions between standing perpendicular spin wave modes (exchange magnons) and longitudinal acoustic phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all metal layers control the frequencies and eigenmodes of acoustic vibrations. The here proposed design allows for achieving and tuning the spectral and spatial modes overlap between phonons and magnons that results in their strong resonant interaction. Realistic simulations for gold-nickel multilayers show that sweeping the external magnetic field should allow for observing resonantly enhanced interactions between individual magnon and phonon modes in a broad range of frequencies spanning from tens of GHz up to several hundreds of GHz, which can be finely tuned through the multilayer design. Our results would enable the systematic study and the deep understanding of resonantly enhanced magneto-elastic coupling between individual phonon and magnon modes up to frequencies of great contemporary fundamental and applied interest.

Strain-induced shape anisotropy in antiferromagnetic structures

We demonstrate how shape-induced strain can be used to control antiferromagnetic order in NiO/Pt thin films. For rectangular elements patterned along the easy and hard magnetocrystalline anisotropy axes of our film, we observe different domain structures and we identify magnetoelastic interactions that are distinct for different domain configurations. We reproduce the experimental observations by modeling the magnetoelastic interactions, considering spontaneous strain induced by the domain configuration, as well as elastic strain due to the substrate and the shape of the patterns. This allows us to demonstrate and explain how the variation of the aspect ratio of rectangular elements can be used to control the antiferromagnetic ground state domain configuration. Shape-dependent strain does not only need to be considered in the design of antiferromagnetic devices, but can potentially be used to tailor their properties, providing an additional handle to control antiferromagnets.

Tunable large spin Nernst effect in a two-dimensional magnetic bilayer

We theoretically investigate topological spin transport of the magnon polarons in a bilayer magnet with two-dimensional square lattices. Our theory is motivated by recent reports on the van der Waals magnets which show the reversible electrical switching of the interlayer magnetic order between antiferromagnetic and ferromagnetic orders. The magnetoelastic interaction opens band gaps and allows the interband transition between different excitation states. In the layered antiferromagnet, due to the interband transition between the magnon-polaron states, the spin Berry curvature which allows the topological spin transport occurs even if the time-reversal symmetry is preserved. We find that the spin Berry curvature in the layered antiferromagnet is very large due to the small energy spacing between two magnonlike states. As a result, the spin Nernst conductivity shows a sudden increase (or decrease) at the phase transition point between ferromagnetic and antiferromagnetic phases. Our results suggest that the ubiquity of tunable topological spin transports in two-dimensional magnetic systems.

Varying critical behaviour of stacked triangular lattice Ising antiferromagnets in the presence of spin–lattice coupling

We perform Monte Carlo simulations on the multilayered triangular-lattice Ising antiferromagnet with six sublattices in the frustrated abab stacking and quantify the impact of spin–lattice coupling on its critical properties in the vicinity of the antiferromagnetic phase transition. By invoking the Einstein site spin–phonon model and by varying the strengths of both antiferromagnetic interlayer exchange interactions and spin–lattice coupling, we compute various thermodynamic observable that characterize how the geometrical frustration and the spin–phonon coupling affect the critical behaviour of the system. Using finite-size scaling, we determine the nature of phase transition and the critical exponents, the latter being found to vary with varying strength of couplings. We find that the transition temperature is more sensitive to the interlayer coupling strength rather than that of magnetoelastic coupling. The variation of critical exponents with the strength of spin–lattice coupling hints to the importance of magnetoelastic interaction in the vicinity of magnetic phase transition in strongly correlated magnetic systems, as already observed in several experiments.

Study of magnetoelastic interaction in MnF2 by the acoustoelectric transformation method

The mechanisms of magnetoelastic interaction in MnF2 are studied using the method of acoustoelectric transformation. The temperature dependence of the piezomagnetic coupling coefficient and its anisotropy were determined in the antiferromagnetic phase. We observe a new effect consisting in the appearance of a non-diagonal component of the magnetic susceptibility tensor, which is proportional to the square of the order parameter, under the action of the shear wave. A phenomenological interpretation of the effect, which takes into account a small-angle rotation of the crystal lattice, is presented. In the paramagnetic state, the effect of acoustic deformation is reduced to the modulation of the diagonal component of the susceptibility tensor.