Magnetic Alloys Research Articles

Reverse Pulse Plating of Thick and Crack-Free Magnetic Layers for MEMS Manufacturing

The integration of hard magnetic alloys in the form of thick films is one of the most interesting challenges for the manufacturing of energy efficient magnetic microelectromechanical systems (MEMS) [1]. With respect to current state of the art devices, whose working principle mostly relies on the exploitation of Lorentzian forces, MEMS based on permanent magnets can potentially present lower power consumption, larger displacements and stronger actuation forces. However, despite these attractive advantages, it is generally difficult to integrate thick hard magnetic layers with currently employed MEMS fabrication techniques.Electrodeposition is a technique that is compatible with MEMS fabrication and is characterized by many significant advantages: high deposition rates, no necessity of a vacuum system, low cost, possibility to deposit alloys and composites. Despite of these advantages, electrodeposition methods capable to yield the thick hard magnetic films suitable for MEMS sensors/actuators have not been successfully developed yet. The reason resides in the problems typically encountered in the deposition of hard magnetic alloys: high residual stress, presence of cracks and inadequate surface finishing.In this context, Reverse Pulse Plating (RPP) may constitute a possible solution to address the challenges of hard magnetic alloys electrodeposition [2]. This technique can significantly reduce internal stresses and hydrogen embrittlement, inhibiting thus cracks formation. In addition, it can simplify electrolyte formulation, eliminating the need of excessive amounts of additives. Finally, it can enhance magnetic properties and refine the grain structure of the deposits, resulting in better mechanical properties.In the present work, RPP of thick and crack-free layers of CoNiP and CoPtP is investigated. These two materials are between the most studied for potential MEMS applications [3, 4]. Indeed, whereas CoPtP offers high coercivities (> 3000 Oe) and excellent remanences, CoNiP represents a low cost alternative characterized by good magnetic properties (with HC up to 2000 Oe). Co-rich CoNiP and CoPtP are deposited from a chloride based acidic electrolyte [3] and from a tartrate based bath, respectively, using ultra-fast RPP. The resulting coatings, characterized by thickness up to 20 µm, are characterized to assess their morphology, phase composition and magnetic behavior.[1] N. M. Dempsey, “Hard Magnetic Materials for MEMS Applications” in: Nanoscale Magnetic Materials and Applications, Springer, Boston, MA (2009)[2] S. Pané et al., Electrochim. Acta 56, 8979-8988 (2011)[3] D. Y. Park et al., Electrochim. Acta 47, 2893-2900 (2002)[4] D. Mallick et al., J. Appl. Phys. 125, 023902 (2019)

Heat Treatment Effect on Thermal, Micro-Crystal Structure and Magnetic Behavior of Ni45Mn40Sn10Cu5 Heusler Shape Memory Alloy

Ni-Mn-Sn-based Heusler alloys are important materials that have potential applications as environmentally friendly smart materials with beneficial properties as well as being magnetic. Both the magnetic field-induced reverse martensitic transformation and the high operating temperature are crucial for the applications of Ni-Mn-Sn-based magnetic shape memory alloys. In this study, martensite transformation temperatures were determined by applying different heat treatments (700 °C, 900 °C, 1100 °C) to Ni45Mn40Sn10Cu5 sample produced by Arc Melter melting method. While reverse conversion was observed in T2 (no heat treatment) and 700°C heat treatment, no reverse conversion was observed at 900°C and 1100°C. When the X-ray diffractogram was examined, martensite phase and γ phase were determined. When the magnetic hysteresis of the samples was examined, it was observed that the magnetic saturation went towards zero with the increase in heat treatment and accordingly, there was a decrease in the magnetization effect.

Fe30Co70/Co/CoxFe3−xO4-δ nanocomposite with multiple magnetic exchange resonance mechanisms and large magnetic loss available for microwave absorption application

Soft magnetic alloys are widely studied and reported as a type of important microwave absorption (MA) materials, while their magnetic losses are limited. In this paper, a multiphase composite strategy of the soft magnetic alloys, hard magnetic metals, and hard magnetic ferrites is adopted for increasing the magnetic loss. Then, three-phase Fe50Co50/CoxFe3−xO4-δ/γ-Fe2O3 (FC31), three-phase Fe30Co70/Co/CoxFe3−xO4-δ (FC22), and three-phase CoxFe3−xO4-δ/Co3O4/Co (FC13) nano-composites are prepared by a simple thermal decomposition process of FeC2O4 and CoC2O4 in vacuum. The crystal structure, surface composition, vibration of chemical bonds, morphology, micro-structure, and static magnetism are characterized by XRD, XPS, FTIR, Raman, SEM, TEM, and SQUID, respectively. The electromagnetic (EM) parameters are measured in 2–18 GHz by a vector network analyzer. Based on the measured EM parameters, the calculated magnetic loss tangents (tanδm) are over 0.5 in a wide frequency band of 8–18 GHz for the FC22/paraffin absorber, showing that the tanδm can be increased dramatically through the multiphase composite strategy. Benefiting from the increased tanδm, an effective absorption bandwidth of 7.0 GHz is achieved for the FC22/paraffin absorber at a thin thickness of 1.45 mm, exhibiting great application advantages in the MA field.

Study on magnetic and structural properties of Fe65Co35 soft magnetic alloy prepared by arc melting and subsequent annealing

Fe65Co35 based soft magnetic alloys (SMAs) have been gaining attention for their superior magnetic features and playing significant roles in composite permanent magnets, magnetic storage and automotive electrification technologies. In the present work, the Fe65Co35 alloy were produced by arc melting with subsequent annealing. The effects of arc melting and annealing upon the structural and magnetic properties of the soft magnetic phase of the alloy Fe65Co35 have been investigated. The variation in magnetic and microstructural characteristics with melting and annealing have been observed using the X-ray diffractometer (XRD), scanning electron microscope (SEM), and the vibrating sample magnetometer (VSM). The XRD patterns verified the existence of the Fe65Co35 alloy. After melting and annealing, the alloy surface morphologies were examined using SEM. In this approach, the Fe65Co35 alloy was annealed at 600 °C for 4 h in an argon environment which resulted in the highest saturation magnetization of 237 emu/g and the lowest coercivity of 31 Oe. The rise in saturation magnetization was attributed to the removal of impurities, during the melting and annealing process.

Valence electron concentration and ferromagnetism govern precipitation in NiFeGa magnetic shape memory alloys

Precipitation is one of a few effective ways enabling to reduce the brittleness of NiFeGa magnetic shape memory alloys. However, the physical origin behind precipitation and the key factors deciding precipitation remain unknown. There is still a lack of available methods to control the precipitation of NiFeGa. To this end, the precipitation of Ni2FeGa is systemically studied by combining first-principles calculations and experimental examinations from the following four aspects: the stability of the matrix, the crystal structure and stability of precipitates, the key factors dominating precipitation and the strategy of tailoring precipitation. Results show that the L21 matrix phase possesses weak elastic and dynamic stabilities, which may be linked to the occurrence of precipitation. It is identified theoretically and experimentally that the precipitate has L12 rather than the previously reported FCC structure. The underlying mechanism was clarified from electron density of state and chemical bond. Valence electron concentration e/a and magnetism are found to be the dominant factors affecting the relative stability of precipitate against matrix with sensitivity coefficients of ‒175.1 and 67.4 meV, respectively. The increase of e/a prefers stabilizing the precipitate, but the enhanced magnetism favors the matrix. Conversely, the influence of lattice volume on precipitation is weak from the aspects of both sensitivity and adjustable range. Lastly, an effective strategy of tuning precipitation, i.e., by tailoring e/a and magnetism, is proposed and verified. This work is expected to lay a theoretical foundation for tailoring precipitation and further optimizing the mechanical and functional performances of ferromagnetic Heusler alloys.

Ti‐Doped Nanocomposite Pr2Fe14B/α‐Fe Ribbons with High Coercivity

Nanocomposite permanent magnetic alloys are prepared by the melt‐spinning technique with wheel speed ranging from 21 to 33 ms−1. X‐ray diffraction results show that the as‐spun ribbon is rich of soft α‐Fe, hard Pr2Fe14B magnetic phases, and no other metastable phases are found in our alloy ribbon. Initial magnetization curves reveal that the coercivity mechanism of the ribbons vary with the content of Ti. For x = 2, coercivity is mainly determined by pure pinning; while for x = 1, 3, and 4, it is mainly controlled by the mixture of nucleation of domain and localized pinning at grain boundaries. The coercivity value of 1026 kA m−1, the highest value reported so far, is mainly generated from a pure pinning mechanism in the ribbon with x = 2. The recoil permeability shows a minimum value range from to for x = 2 alloy, suggesting strong exchange coupling between the magnetic grains and then leading to the concurrent reversal of soft and hard phase grains during the demagnetization process. The Henkel plots demonstrate only exchange interaction for x = 1 and exchange interaction with slightly magnetostatic interaction for x = 2, 3, and 4. The exchange interaction exhibits maximum strength for x = 2, which is the reason for high coercivity.

Characterization of Fe-6Si Soft Magnetic Alloy Produced by Laser-Directed Energy Deposition Additive Manufacturing

Commercial electrical steels, Fe-Si alloys with < 4 wt.% Si, are inexpensive and efficient materials for electrical power conversion. Further efficiency improvements require increasing the silicon concentration to 6 wt.%, at which point the material becomes brittle and difficult to form by conventional rolling and sheet fabrication methods. Additive manufacturing stands to overcome challenges with commercial manufacturing techniques by leveraging near-net-shape fabrication. The wide array of process conditions provides additive manufacturing with increased flexibility, enabling control over the microstructure and mechanical properties. This work explores the microstructures and magnetic properties of ring-shaped Fe-Si alloys produced using concentric and cross-hatch tool paths on a laser-directed energy deposition additive manufacturing system. Concentric-built samples exhibit elongated grain structures while cross-hatch-built samples comprise lower aspect ratio grain structures. Thermal finite element analysis simulations model the stress conditions produced by the different scan path geometries. Microhardness measurements probe the mechanical properties as a function of anneal temperature, providing a qualitative understanding of the intergranular defect density. Soft magnetic properties measured under quasistatic and AC conditions show frequency- and microstructure-dependent coercivity and permeability. Finally, analysis of the core loss quantifies how the build strategies and thermal treatments influence efficiency in electrical power conversion applications. Understanding the influences of scan path geometry and thermal treatment provides a pathway towards application of additively manufactured soft magnetic materials.

Development of Soft Magnetics Fe-B-C-Si Amorphous Alloys with High Magnetization and Sufficient Amorphous-Forming Ability

The amorphous-forming ability (AFA) and the magnetic properties of the amorphous Fe-B-C-Si soft magnetic alloys have been investigated. Though the ternary Fe-B-C alloys exhibit high magnetization, their AFA is poor, which has prevented their practical application. It was confirmed that the addition of Si to the Fe-B-C alloys significantly improves AFA. Furthermore, it has been found that the composition range of the Fe-B-C-Si alloys with sufficient AFA can be identified by focusing on the enthalpy of mixing (ΔHmix) and δ, which is related to the ratio of atomic radius between the constituent elements, of the alloys. The Fe-B-C-Si amorphous alloys that combine the high saturation magnetization of 175−177 A m2/kg with sufficient AFA to produce thick sheets whose thickness of 70 μm or more have been successfully developed by using the relationship between ΔHmix, δ and AFA as a guideline. The Fe-B-C-Si amorphous alloys are expected to be applied to core materials for various magnetic components.

Mass Production and Vast Application States of Bulk Metallic Glasses

Since the first synthesis of bulk metallic glasses (BMGs) by copper mold casting in 1990, much effort has been devoted to the searching of new BMG composition, the clarification of fundamental and engineering properties for BMGs and their industrialization. At present, BMGs have been formed in a large number of multicomponent alloy systems where the empirical three component rule is satisfied. Nowadays, commercialized BMGs are classified to Zr-based and Fe-based alloy groups. When we look at the industrialization of Zr-Al-Ni-Cu-based BMGs, the first commercialization was made for golf clubs in Japan in 1998, followed by watch parts etc. Since then, Zr-based BMGs have been used continuously up to 2013, though their application scale was in a limited state. Since 2014, the application scale was significantly extended in collaboration with the rapid developments of smartphones and electric vehicles. At present, the mass production facilities for Zr-based BMGs have been significantly developed and variety of BMG products have been produced. On the other hand, Fe-based soft magnetic BMGs were found in 1995. Their BMGs have also been used on a huge number of pieces in various kinds of electronic-magnetic instruments. These recent application states for Zr- and Fe-based BMGs are introduced together with new nanocrystalline Fe-based soft magnetic alloys developed through the derivation of alloy composition from Fe-based BMGs.

Influence rules of early transition elements on rapid solidified structure and nanocrystallization behaviors of Fe-Si-B-Cu soft magnetic alloys with high Cu content

Unique rapid solidified structure and nanocrystallization mechanism enable the Fe-based nanocrystalline alloys with high Cu content excellent soft magnetic properties and good manufacturability, and also results in unusual phenomena in terms of alloying effects. In the present work, we systematically studied the influence rules of early transition elements on the rapid solidified structure and nanocrystallization behaviors of Fe-Si-B-Cu soft magnetic alloys with high Cu content and explored the related mechanisms. In terms of rapid solidified structure, the additions of early transition elements always inhibit the formation of pre-existing α-Fe crystals even eliminate them, and the additions that could produce larger atomic mismatch parameter (δ) and negative mixing enthalpy (ΔHmix) show stronger effects. In terms of nanocrystallization behaviors, the increases in δ and negative ΔHmix weaken the competitive growth between the pre-existing nanocrystals during annealing and then coarsen the nanostructure of the annealed alloys and deteriorate their magnetic softness, while the excessive increases in δ and negative ΔHmix could significantly suppress the growth of α-Fe crystals by diffusion inhibition during annealing and thus remarkable refine the nanostructure of the annealed alloys and improve their magnetic softness.

Clean production of Fe-based amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore and apatite

Clean production of Fe-based amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore and apatite

Spatially Tuned Properties in a Bulk Fe–Co Soft Magnetic Alloy via Transverse Induction Annealing and Feasibility Study for Motor Applications

Electric vehicle adoption has seen a dramatic upward trend in the last decade. Maximal efficiency of electric motor technology for maximum range, achieved by minimizing losses experienced by motor stator and rotor, is limited by a trade‐off with high strength, as necessary to withstand torque experienced during operation. Spatial tailoring of magnetic and mechanical properties for optimized magnetic performance while retaining sufficient mechanical strength is a desirable pathway toward improved performance. Here, radiofrequency transverse induction annealing is demonstrated as a novel pathway to continuous spatial variation in microstructure of bulk crystalline soft magnetic alloys, providing a novel processing route to spatially tuned properties. Via local control of grain size, magnetic and mechanical properties may be separately prioritized as functions of position, enabling optimized stator laminations with reduced losses while retaining requisite mechanical strength. Experiment and finite element modeling demonstrate that a cylindrical induction coil can impose significant microstructure and property variation in a Fe–Co bulk crystalline soft magnetic alloy. A basic feasibility study follows, examining improved performance of a motor containing a stator with radial variation in coercivity. Results indicate future potential for co‐optimization of spatial thermal processing of magnetic laminations with motor designs for unprecedented performance.

Tuning of the magneto-caloric effects in Ni43Mn46In11 magnetic shape memory alloys by substitution of boron

In this study, we report the structural, magnetic, and magnetocaloric properties of B substitution on the Mn site in Ni43Mn46−x B x In11(x = 0.5, 1.0) Heusler alloys. Crystal structure analysis using room-temperature x-ray diffraction data reveals both samples have mixed phases composed of cubic and tetragonal phases. The structural and magnetic phase transition characteristic temperatures are determined using differential scanning calorimetry, isothermal magnetization (MT), and isofield magnetization (MH) measurements. Both alloys exhibit inverse and direct magnetocaloric effects in the vicinity of their magnetostructural transition and Curie temperature (T C), respectively. For Ni43Mn45.0B1.0In11 a maximum magnetic entropy change of 25.06 J kg−1 K−1 is observed at 250 K for a magnetic field change of 5 T.

AIMD study and experimental verification of Ge-doped Fe80P13C7 amorphous soft magnetic alloys

Fe80P13-xC7Gex (x = 0, 2, 4) amorphous alloys were synthesized by rapid solidification technique and studied using Ab-initio molecular dynamics (AIMD) and first-principles calculations based on density-functional theory (DFT) for their electronic structures. Brillouin function was used to calculate saturation magnetization (µ0MS) at elevated temperatures utilizing experimentally measured Curie temperature (TC) and µ0MS at 0 K calculated by DFT.To verify the calculated µ0MS, ingots of Fe80P13-xC7Gex (x = 0, 1, 2, 3, 4, 5, 6) alloy were prepared by melt-spinning. An increase in experimental µ0MS with Ge concentration agrees with the calculated µ0MS. TC also increases with Ge concentration. Partial substitution of Ge for P enhances the µ0MS to 1.63 T (x = 4) from 1.46 T (x = 0), which indicated that the Fe80P13-xC7Gex (x = 4) shows optimum soft magnetic properties.

Constrained DFT-based magnetic machine-learning potentials for magnetic alloys: a case study of Fe–Al

We propose a machine-learning interatomic potential for multi-component magnetic materials. In this potential we consider magnetic moments as degrees of freedom (features) along with atomic positions, atomic types, and lattice vectors. We create a training set with constrained DFT (cDFT) that allows us to calculate energies of configurations with non-equilibrium (excited) magnetic moments and, thus, it is possible to construct the training set in a wide configuration space with great variety of non-equilibrium atomic positions, magnetic moments, and lattice vectors. Such a training set makes possible to fit reliable potentials that will allow us to predict properties of configurations in the excited states (including the ones with non-equilibrium magnetic moments). We verify the trained potentials on the system of bcc Fe–Al with different concentrations of Al and Fe and different ways Al and Fe atoms occupy the supercell sites. Here, we show that the formation energies, the equilibrium lattice parameters, and the total magnetic moments of the unit cell for different Fe–Al structures calculated with machine-learning potentials are in good correspondence with the ones obtained with DFT. We also demonstrate that the theoretical calculations conducted in this study qualitatively reproduce the experimentally-observed anomalous volume-composition dependence in the Fe–Al system.

Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100-fs time scales.

The direct manipulation of spins via light may provide a path toward ultrafast energy-efficient devices. However, distinguishing the microscopic processes that can occur during ultrafast laser excitation in magnetic alloys is challenging. Here, we study the Heusler compound Co2MnGa, a material that exhibits very strong light-induced spin transfers across the entire M-edge. By combining the element specificity of extreme ultraviolet high-harmonic probes with time-dependent density functional theory, we disentangle the competition between three ultrafast light-induced processes that occur in Co2MnGa: same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast spin flips mediated by spin-orbit coupling. By measuring the dynamic magnetic asymmetry across the entire M-edges of the two magnetic sublattices involved, we uncover the relative dominance of these processes at different probe energy regions and times during the laser pulse. Our combined approach enables a comprehensive microscopic interpretation of laser-induced magnetization dynamics on time scales shorter than 100 femtoseconds.

Decomposition in Mn50Ni40In10 melt-spun ribbons and its influence on magnetic properties

The phase stability, decomposition and its influence on the martensitic transformation and magnetic properties of magnetic shape memory alloy (MSMA) Mn50Ni40In10 melt-spun ribbons were investigated experimentally and theoretically. As-spun Mn50Ni40In10 was fine single Heusler phase with pronounced martensitic and magnetic transition below room temperature. However, in differential scanning calorimetry measurement an exothermic peak at 690 K and an endothermic peak at 765 K is observed during the heating of as-spun ribbons. The two peaks correspond to the growing of the punctiform precipitates in the grain interiors and the formation of a large amount of grain boundary segregation, respectively. After annealing at 870 K, the ribbon samples decompose into a cubic In-rich phase at grain boundaries and In-poor 7 M−modulate martensitic phase in the matrix. After annealing at 690 K and above, the martensitic transformation below room temperature is strongly weakened. Annealing temperature also has obvious influence on the 5 and 300 K saturation magnetization Ms of Mn50Ni40In10. Theoretical calculations on Mn2Ni1.5In0.5 (Mn50Ni37.5In12.5) give a negative formation energy (-0.11 eV/ f.u.) and a positive decomposition energy (0.22 eV/f.u.), indicating that this alloy can be metastable and tends to decompose into Mn2NiIn cubic phase and NiMn martensite, agreeing with the experimental results qualitatively.

Modulated Kondo screening along magnetic mirror twin boundaries in monolayer MoS2

When a single electron is confined to an impurity state in a metal, a many-body resonance emerges at the Fermi energy if the electron bath screens the impurity’s magnetic moment. This is the Kondo effect, originally introduced to explain the abnormal resistivity behaviour in bulk magnetic alloys, and it has been realized in many quantum systems over the past decades, ranging from heavy-fermion lattices down to adsorbed single atoms. Here we describe a Kondo system that allows us to experimentally resolve the spectral function consisting of impurity levels and a Kondo resonance in a large Kondo temperature range, as well as their spatial modulation. Our approach is based on a discrete half-filled quantum confined state within a MoS2 grain boundary, which—in conjunction with numerical renormalization group calculations—enables us to test the predictive power of the Anderson model that is the basis of the microscopic understanding of Kondo physics.

Investigation of rare earth lean Sm-(Fe,Co)-Mo alloys for permanent magnets

Bulk magnets with the composition of Sm1Fe10.5−xCoxMo1.5 (where x = 0, 1, and 2) with the tetragonal ThMn12 structure were prepared and their intrinsic magnetic properties were studied. The cast samples were then subjected to high-energy-ball-milling (HEBM), followed by hot-compaction at 650 °C. The compacted samples were annealed at temperatures ranging from 700 °C to 1000 °C to obtain high coercivity. The effects of Co on the magnetic properties, including the Curie temperature TC, saturation magnetization MS, anisotropy field HA, and energy product (BH)max were investigated. It is observed that Co substitution increases the Curie temperature, the saturation magnetization, and the remanence, but decreases the anisotropy field and the coercivity. Among the investigated samples, the isotropic Sm1Fe9.5Co1Mo1.5 showed the highest energy product (21.5 kJ/m3) after annealing at 750 °C for 48 h, marking a 23 % enhancement relative to our specimen without cobalt substitution.

Itinerant ferromagnetism and room temperature giant magnetocaloric effect in (Mn0.6Fe0.4) (Ni0.5Co0.5) Si shape memory alloy

In this article, the feasibility of obtaining a magneto-structural coupling over a wide working temperature range of about 127 K (from 206.5 K to 333.5 K) with negligible thermal hysteresis in combination with the structural, microstructural, magnetic, and magnetocaloric properties of a 50 % Co-doped (at the Ni site) polycrystalline (Mn0.6Fe0.4) (Ni0.5Co0.5) Si (MFNCS-0.5) magnetic shape memory alloy (MSMA) has been thoroughly investigated. Along with leaf-like microstructure, at room temperature, the system shows a mixed phase of TiNiSi type low-temperature high-magnetic (ferromagnetic) orthorhombic martensite and Ni2In type high-temperature low-magnetic (paramagnetic) hexagonal austenite, with the dominance of the second one. To estimate the magnetocaloric effect (MCE) across the phase transition, the isothermal magnetic measurement technique has been employed. The merging of heating and cooling iso-field thermo-magnetization (M-T) curves, the presence of negligible thermal hysteresis in the MH curves, universal magnetic entropy curves, a proposed phenomenological model (across the Curie temperature), and the positive slopes of the Arrott plot (Banerjee criterion) show that the first-order structural and magnetic transition are coupled along with a second-order ferromagnetic to paramagnetic (FM → PM) phase transition (SOPT). By extrapolating the Arrott plot to the H/M = 0 axis the spontaneous magnetization value very close to 0 K, Ms(0), is found to be 71.92 emu/g (∼1.83 µB/f.u.). The linear dependency of MS2T on T2 below SOPT and the RWR (Rhodes–Wolhfarth ratio) = 4.29 > 1 indicate the long-range itinerant ferromagnetism in this alloy. A giant magnetic entropy change (ΔSm) of 25.77 J kg−1 K−1 and a refrigerant capacity (RC) of 472.83 J kg−1 are obtained at 6 T field. This observed magnetic refrigerant's key characteristics, including a giant magnetocaloric effect (MCE) near room temperature (RT), negligible thermal hysteresis loss, a wide operating temperature range of 127 K, and the use of cost-effective, non-toxic constituent elements, make it a suitable and very promising member for applications in solid-state refrigeration technology near RT.