Ferromagnetic Alloys Research Articles

Magnetostriction of Heusler Ferromagnetic Alloy, Ni2MnGa0.88Cu0.12, around Martensitic Transition Temperature

In this study, magnetostriction measurements were performed on the ferromagnetic Heusler alloy, Ni2MnGa0.88Cu0.12, which is characterized by the occurrence of the martensitic phase and ferromagnetic transitions at the same temperature. In the austenite and martensite phases, the alloy crystallizes in the L21 and D022-like crystal structure, respectively. As the crystal structure changes at the martensitic transition temperature (TM), a large magnetostriction due to the martensitic and ferromagnetic transitions induced by magnetic fields is expected to occur. First, magnetization (M-H) measurements are performed, and metamagnetic transitions are observed in the magnetic field of μ0H = 4 T at 344 K. This result shows that the phase transition was induced by the magnetic field under a constant temperature. Forced magnetostriction measurements (ΔL/L) are then performed under a constant temperature and atmospheric pressure (P = 0.1 MPa). Magnetostriction up to 1300 ppm is observed around TM. The magnetization results and magnetostriction measurements showed the occurrence of the magnetic-field-induced strain from the paramagnetic austenite phase to the ferromagnetic martensite phase. As a reference sample, we measure the magnetostriction of the Ni2MnGa-type (Ni50Mn30Ga20) alloy, which causes the martensite phase transition at TM = 315 K. The measurement of magnetostriction at room temperature (298 K) showed a magnetostriction of 3300 ppm. The magnetostriction of Ni2MnGa0.88Cu0.12 is observed to be one-third that of Ni50Mn30Ga20 but larger than that of Terfenol-D (800 ppm), which is renowned as the giant magnetostriction alloy.

A Terahertz Radiation Linear Polarizer Based on Using a Magnetic Fluid in an External Magnetic Field

A model of a magnetically controlled linear polarizer of terahertz (THz) waves based on a cell filled with a magnetic fluid and controlled by an external magnetic field was proposed. The magnetic fluid consisted of a synthetic oil with high transparency in the THz range and ferromagnetic alloy microparticles. Selection of the ferromagnetic particles size and concentration, and also parameters of the external magnetic field was conducted. It was shown that when using ferromagnetic particles of 10–35 μm size, a concentration of 10 wt.%, and a magnetic field with induction of 6.7–57.2 mT, the created construction works as a linear polarizer of the THz wave in the ranged from 0.3 to 1.5 THz, with the degree of polarization of the initially non-polarized THz wave transmitted through the cell being at least of 80%.

Comparative study of femtosecond laser-induced ultrafast magnetization dynamics in soft ferromagnetic ultra-thin alloy

The typical demagnetization mechanism is applicable in magneto-optic recording systems on a nanoseconds timescale. Interest in this area has expanded rapidly since understanding the physics of ultrafast magnetization processes by experiment are an acutely challenging task. As a result, in order to explain the quenching of magnetization by laser heating in ferromagnetic alloys such as permalloy, we executed a new theoretical study on permalloy, as well as Ni and Fe ultra-thin films with thickness varying from 1 nm to 5 nm. In particular, we demonstrate that the magnetization decays in a timescale of about 0.1 picosecond by the microscopic three-temperature model. Our free electron model-based theoretical model represents that electron–phonon coupling coefficient and demagnetization time in the thin-films are strongly sensitive to film thickness, pulse duration and laser fluence, respectively. In particular, we show that the rapid demagnetization (100 fs) is due to electron-magnon excitation. This feature improves data processing speed in communication systems and the recording industry.

Microstructural and crystallographic characteristics of martensite micro-variants in NiMnGa-based ferromagnetic alloy

A systematic investigation on microstructural and crystallographic characteristics of martensite micro-variants in Ni54Mn25Ga20.9Dy0.1 ferromagnetic shape memory alloy was performed. The alloys exhibited a dual-phase microstructure consisting of self-accommodated tetragonal martensite and hexagonal Dy-rich dispersive precipitates. In each colony, four distinct micro-variants with different crystallographic-orientations existed, where the adjacent variant pairs connected by crossing-interfaces possessed a non-twinned relationship and other pairs connected by extending-interfaces were twin-related to each other. The corresponding twinning planes and directions were {112} and 〈111〉, respectively. Nevertheless, the twinning relationships of these twin-related micro-variant pairs were not perfect, which contained a small rotation. Interface analysis demonstrated that these two types of interface planes coincide with the orientation relationship planes and twinning planes of their connecting micro-variants, respectively.

Prospects to Use Amorphous Fe–Ni–Si–B Ribbons in Contactor Cores

We consider the possibility to use an amorphous Fe–Ni–Si–B material in the core of contactors, which are widely used in connecting and disconnecting electric circuits, instead of the crystalline material of 3% electric steel. Alloys containing Fe–Ni–Si–B have been treated with the use of mechanical, thermomechanical, and magnetic fields, and the material for practical applications has been obtained. The processing modes were chosen so that a change in the performance of ferromagnetic (below the Curie temperature) alloys during the annealing could be controlled. The obtained specimens were annealed in oil at 360 ∘C in a magnetic field of 200 A/m for 200 min. The temperature mode was chosen so that the stress relaxation could occur during the annealing, and the structural changes in the material could be observed.

Revealing magnetic correlations in ferromagnetic alloys with polarized SANS

We search for magnetic correlations at the nanoscale in a ferromagnetic alloy with low critical temperature Tc and reduced magnetic moments. We present a small-angle neutron scattering (SANS) study of the binary alloy Ni0.89 V0.11 close to the quantum critical point where the ferromagnetic order is destroyed towards a paramagnetic phase by sufficient V concentration. We demonstrate the challenge and the advantage of a fully polarized SANS analysis to discriminate the small magnetic components from the dominant nuclear contributions. We focus on the azimuthal angle dependence of selected cross sections, like pure spin-flip and non spin-flip asymmetry, to finally reveal magnetic contributions at different length scales.

On the Possible Half-Metallic Properties of Fe2RhZ (Z = Al, Si, Ga, Ge, In, Sn) Ferromagnetic Heusler Alloys

The possible presence of half-metallic properties in Fe2RhZ (Z = Al, Si, Ga, Ge, In, Sn) ferromagnetic Heusler alloys is ab initio studied. The calculation is carried out taking into account the exchange correlation effects using the generalized and meta-generalized gradient approximations. It is shown that the ground state of most investigated alloys is ferromagnetic ordering in the Тр model lattice. An analysis of the phase stability of the alloys showed that, in the considered approximations, most of them are stable in both the regular and inverse lattice, as well as in the three model lattices belonging to inverse-type Heusler structures with different atomic orders. It was predicted using the strongly constrained and appropriately normed (SCAN) functional that the Fe2RhSi alloy can exhibit the properties of half-metals, since it has an integer magnetic moment, a fairly high degree of polarization, and an energy gap at the Fermi level of spinup electrons.

Regularities of Functional Properties in Stress-Induced Aged Martensite Single Crystals of Ni51Fe18Ga27Co4 Ferromagnetic Alloy

Regularities of Functional Properties in Stress-Induced Aged Martensite Single Crystals of Ni51Fe18Ga27Co4 Ferromagnetic Alloy

Surface Morphology and Exchange Bias Anisotropy Studies in Large Area Deposited Co2FeSi Ir50Mn50 Multi Layers For Spintronic Applications

Surface morphology and magnetic properties of ferromagnetic Heusler alloy Co2FeSi thin films and their multi-layers with anti-ferromagnetic Ir50Mn50, which find applications in spintronic devices were investigated. The sputtering process flow for large area deposition of thin films on 3 inch size thermally oxidized single crystal Si(100)/SiO2 substrates have been developed by optimizing the sputtering geometry and other process parameters. A uniform film composition, thickness, smooth surface, good crystallinity and magnetic properties have been achieved in the films over 3-inch size wafers. The isotropic magnetic properties such as saturation/remanent magnetizations, coercivity were achieved in Co2FeSi films deposited on 3-inch size Si(100)/SiO2 wafers with 15 nm Cr buffer layer. An exchange bias anisotropy has been established in Co2FeSi/IrMn multilayer by magnetic annealing process using in-house made magnetic annealing set up. A maximum exchange bias anisotropy field, Hex of 178 Oe and low coercivity, Hc of 85 Oe has been achieved in the Co2FeSi/IrMn multilayer stacks suitable for magnetic tunnel junctions for spintronic applications.

Current-induced crystallisation in a Heusler-alloy-based giant magnetoresistive junction for neuromorphic potentiation

Recent development in neuromorphic computation allows us to achieve low power and highly efficient calculations better than the conventional von Neumann computation. In order to achieve realistic synaptic operation, potentiation to add weighting to strengthen a selected artificial synapse. Such functionality can be achieved by reducing the electrical resistance of the artificial synapse. Recently, a ferromagnetic Heusler alloy used in a magnetoresistive junction has been demonstrated to crystallise via the layer-by-layer mode by introducing an electrical current pulse. In this study, we have extended the current-induced crystallisation to a junction with epitaxially-grown Heusler alloy after post-annealing for crystallisation. By combining this potentiation functionality with the neuromorphic operation, realistic synaptic computation can be developed.

Influence of magnetic relaxation on magnetoelastic resonance-based detection

The phenomenon of magnetic relaxation in amorphous ferromagnetic alloys can result in an undesired time evolution of the magnetization that produces serious drawbacks in the use of these materials in sensor applications. The present work studies, at room temperature, the influence of magnetic relaxation on the performance of an amorphous ferromagnetic ribbon as the main element of a magnetoelastic resonance (MER)-based sensor. The time evolution was observed through the evolution of the MER signal, in particular through the variation experienced by the resonance frequency , which is the main parameter used for sensing. It is found that, after the bias field is changed to a given value, and under constant excitation conditions, increases with time in a typical relaxation behavior with a relaxation amplitude and a relaxation time that depend on the excitation conditions. The amplitude of the excitation h turned out to be a key factor on the relaxation, since larger excitation field amplitudes (h mOe) result in a considerable decrease of relaxation times ( and a reduction of the variation of the resonance frequency (). The influence of this relaxation on the sensor performance and the possible approaches to overcome this problem are evaluated and applied to the case of a magnetoelastic sensor, operating as mass sensor, for monitoring a chemical precipitation reaction.

Ordering-induced Elinvar effect over a wide temperature range in a spinodal decomposition titanium alloy

Temperature-independent elastic modulus is termed as Elinvar effect, which is available by tuning the continuous spin transition of ferromagnetic alloys via composition optimization and the first-order martensitic transformation of shape memory alloys via plastic deformation. However, these reversible mechanisms are restricted generally in a narrow temperature range of less than 300 K. Here reports, by tuning a spinodal decomposition in a Ti-Nb-based titanium alloy via aging treatment, both the Elinvar effect in a wide temperature range of about 500 K and a high strength-to-modulus ratio of about 1.5% can be obtained by a continuous and reversible crystal ordering mechanism. The results demonstrate that the alloy aged at 723 K for 4 h has a nanoscale plate-like modulated β+α" two-phase microstructure and its elastic modulus keeps almost constant from 100 to 600 K. Synchrotron and in-situ X-ray diffraction measurements reveal that the crystal ordering parameter of the α" phase increases linearly with temperature from 0.88 at 133 K to 0.97 at 523 K but its volume fraction keeps a constant of about 33.8%. This suggests that the continuous ordering of the α" phase toward the high modulus α phase induces a positive modulus-temperature relation to balance the negative relation of the elastically stable β phase. The aged alloy exhibits a high yield strength of 1200 MPa, good ductility of 16% and a high elastic admissible strain of 1.5%. Our results provide a novel strategy to extend the Elinvar temperature range and enhance the strength by tuning the crystal ordering of decomposition alloys.

Evolution of short-range magnetic correlations in ferromagnetic Ni-V alloys

We experimentally study how the magnetic correlations develop in a binary alloy close to the ferromagnetic quantum critical point with small-angle neutron scattering (SANS). Upon alloying the itinerant ferromagnet nickel with vanadium, the ferromagnetic order is continuously suppressed. The critical temperature Tc vanishes when vanadium concentrations reach the critical value of xc=0.116 indicating a quantum critical point separating the ferromagnetic and paramagnetic phases. Earlier magnetization and $\mu$SR data have indicated the presence of magnetic inhomogeneities in Ni(1-x)V(x) and, in particular, recognize the magnetic clusters close to xc, on the paramagnetic and on the ferromagnetic sides with nontrivial dynamical properties [R. Wang et al., Phys. Rev. Lett. 118, 267202 (2017)]. We present the results of SANS study with full polarization analysis of polycrystalline Ni(1-x)V(x) samples with x=0.10 and x=0.11 with low critical temperatures Tc below 50 K. For both Ni-V samples close to xc we find isotropic magnetic short-range correlations in the nanometer-scale persisting at low temperatures. They are suppressed gradually in higher magnetic fields. In addition, signatures of long-range ordered magnetic domains are present below Tc. The fraction of these magnetic clusters embedded in the ferromagnetic ordered phase grows towards xc and agrees well with the cluster fraction estimate from the magnetization and $\mu$SR data. Our SANS studies provide new insights into the nature of the inhomogeneities in a ferromagnetic alloy close to a quantum critical point.

COMPARISON OF MODELS OF MAGNETIZATION CURVES AND HYSTERESIS LOOPS ACCORDING TO THE GILES-ATHERTON MODEL FOR SOFT MAGNETIC AMORPHOUS ALLOYS

The subject of research in the article is ferromagnetic soft magnetic amorphous materials and alloys, which are used in power sources of automated control systems, and in vehicle electrical installations. The aim of the work is an objective comparison of two magnetization models for soft magnetic amorphous alloys - the main magnetization curve using approximation functions and the Giles-Atherton hysteresis loop model. In the study, the least squares method was used to optimize the main magnetization curve and the Giles-Atherton hysteresis loop optimization method with the aim of its maximum coincidence with the experimentally obtained loop. Experimental and reference data for common types of magnetically soft amorphous alloys were used for modeling. As a criterion of model accuracy for both modeling methods, the relative error in determining the magnetic induction value was chosen, and the experimental value obtained from the real hysteresis loop of a magnetically soft amorphous alloy was taken as its exact value, and the approximate value was taken from calculations of the magnetic induction value using the methods of approximating the magnetization curve and simulation of the hysteresis loop using the Giles-Atherton method. As a result of the research, it was revealed that both models of magnetization of magnetically soft amorphous materials give simulation results similar in accuracy. The obtained results of the study can be used to select an appropriate magnetization model for the mathematical description of ferromagnetic devices using magnetically soft amorphous metals and alloys. The final conclusion about the advantages of a particular model can only be made on the basis of the ultimate goals of the analysis.

Development of an Autonomous Magnetic Permeability Sensor

In our days, there is an undeniable need for control over the quality of metals in machines, metal components, tools, and construction materials during production and maintenance. Nondestructive testing sensors have been proven to be the most effective way of determining the quality of the composition of materials since they can detect flaws, not only during their construction but also during maintenance, without interfering with, or obstructing, their use. This article focuses on the measurement of the magnetic permeability of ferromagnetic steels and alloys as a nondestructive method of correlating magnetic properties with residual stresses based on the use of a yoke-shaped sensor. Most importantly, an electromagnetic energy harvesting system has been designed and tested, based on the exploitation of mechanical vibrations. The combination of the sensor and the energy harvesting system can lead to an energy autonomous device, which can be placed in inaccessible locations for remote nondestructive testing where measurements can be taken and transmitted autonomously every 10 min. Said transmission is realized by a network of yoke sensors in multiplex configuration and sent to a central sensor, leading to an Internet of Things usable device.

Measurement of the spin-wave stiffness and energy gap in the magnon spectrum of amorphous ferromagnets by small-angle scattering of polarized neutrons

This work studies the magnetic excitations of amorphous ferromagnetic alloys (Fe40Ni40P14 11B6 and Fe48Ni34P18) by small-angle polarized neutron scattering in the geometry when the magnetic field is inclined towards the neutron beam direction. Polarized neutrons are used in order to extract the scattering arising from the spin waves only. In this case, the energy-integrated neutron cross section contains a component which depends on neutron polarization and has a left–right asymmetry in the plane determined by the directions of the field and the neutron beam. Small-angle polarized neutron scattering measurements on spin waves in amorphous iron–nickel alloys were performed at different values of the external magnetic field H and neutron wavelength λ. The spin-wave spectrum is quadratic in terms of the momentum transfer and contains both a field gap and an inherent gap Δ of a non-field nature: E q = Aq 2 + gμB H + Δ. Only by measuring simultaneously two dependencies of the cut-off angle θc – on the applied magnetic field and on the neutron wavelength – is it possible to obtain reliable information about the spin-wave stiffness and the spin-wave gap in these amorphous ferromagnetic systems.

Enhancement of thermoelectric performances in n-type RbCrZ (Z = S, Se, Te) half-metallic ferromagnetic alloys via charge carrier concentration or chemical potential

We used first-principles simulations to examine the magnetic, elastic, and thermoelectric properties of RbCrZ (Z = S, Se, and Te) half-Heusler alloys. Our results indicate that RbCrZ (Z = S, Se, and Te) alloys are completely spin-polarized half-metallic ferromagnets in the ground state. Elastic constants provide mechanical stability. Unlike RbCrS and RbCrSe, RbCrTe is brittle and unable to withstand thermal shocks. RbCrS is the most anisotropic material, while RbCrSe is the most isotropic. The greatest ZT values in the spin-down channel for RbCrS, RbCrSe, and RbCrTe are 0.81355, 0.62249, and 1.02846, respectively. To attain this value, the charge carrier concentration must be lowered to n = - 3.18119 × 1022 cm−3 for RbCrS, n = - 5.32817 × 1022 cm−3 for RbCrSe, and for RbCrTe, the charge carrier concentration must be enhanced to n = - 4.99321 × 1022 cm−3. The decrease of the chemical potential of RbCrS, RbCrSe, and RbCrTe by 0.02, 0.084, and 0.0329 Ryd, respectively, resulted in identical values.

Prospects for using amorphous ferromagnetic alloy microwire for reinforcement of cement mortar

Traditionally, fibers for fiber-reinforced concrete are made of metal, polypropylene, basalt or glass. На сегодняшний день для строительства актуально использование волокон с уникальными электрофизическими свойствами. The possibilities of using a microwire made of an amorphous ferromagnetic alloy based on cobalt with a shell of borosilicate glass in concrete technologies are studied in this paper. The influence of the content of fibers of different sizes (length 7 and 15 mm) on the rheological and physico-mechanical properties of the solution was established. The deterioration of the workability of mixtures and the average density of the composite with the introduction of the studied fiber is shown. It has been established that the spread diameter of the mortar mixture with a fiber content of 0.5...3.0 % by weight of Portland cement is reduced by 9.8...26.1% compared to the control composition. It is shown that the short fiber (7 mm) at the maximum content (3 %) leads to a more significant decrease in the average density (up to 9.6 %) compared to the long fiber (15 mm) of the same concentration (reduction is no more than 4 %). A positive effect on the flexural strength and crack resistance of the solution was established. The increment of flexural and compressive strength ranges from 1.11 to 1.54 and from 0.99 to 0.78 respectively with increasing fiber concentration. The presence of fiber in the composition of the solution allows you to increase the crack resistance from 0.098 to 0.164. The increase in the crack resistance coefficient for compositions with a fiber 7 mm long is 51...68 % and compositions with a fiber 15 mm long is 22...37 %. The possibility of using such microwire based on a ferromagnetic alloy for dispersed reinforcement of cement solutions opens up prospects for the creation of “smart” materials.

The Magnetic Susceptibility of Alloys Below the Percolation Threshold

Within the theory of random interaction fields, the possibility of determining the Curie point and the paramagnetic Curie point corresponding to the appearance of short-range order is shown. In ferromag-netic alloys, there is a concentration range in which the long-range order is destroyed, but the short-range order persists. This leads to the appearance of a cluster glass phase, which is characterized by a time depen-dence of the magnetic susceptibility and the appearance of viscous magnetization. For an AuFe alloy as an example, the behavior of the initial magnetic susceptibility as a function of temperature and concentration is studied and compared with experimental data.

Anomalous critical supercurrent and half-integer Shapiro steps based on Josephson junction of topological insulator nanowires

Topological insulator-based Josephson junction, as a candidate device for searching for Majorana zero energy modes, has attracted much attention. One of the key issues along this direction is to fabricate Josephson junctions with high-quality interfaces, hoping to searching for 4π-period current-phase relation in topologically non-trivial Josephson junction. In this work, the Josephson junctions based on three-dimensional topological insulator nanowires Bi<sub>2</sub>Te<sub>3</sub> and Bi<sub>2</sub>(Se<sub><i>x</i></sub>Te<sub>1–<i>x</i></sub>)<sub>3</sub> are fabricated to study their superconducting proximity effects, multiple Andreev reflections, and current-phase relations. A number of interesting phenomena are observed, including the anomalous enhancement in junctions’ critical supercurrent with magnetic field, and the appearance of half-integer Shapiro steps in the ac Josephson effect. And, we discuss the possible origins of the observed anomalous behaviors in general, and their relation with the ferromagnetic layer of TiTe alloy formed at the interface between the topological insulator nanowires and the Ti buffer layer of the metallic electrodes, in particular. We provide the experimental evidence for the formation of a ferromagnetic TiTe alloy layer at the interface of our device. And, we believe that the formation of such a layer in our Josephson device breaks the time reversal symmetry, leading to the observed anomalous enhancement of the critical supercurrent with magnetic field, as well as the appearance of half-integer Shapiro steps. Our results suggest that to study the topologically non-trivial behaviors such as 4π-period current-phase relation, one still needs to improve the interface quality of the superconductor-normal metal-superconductor type of Josephson junction devices.