Ferromagnetic Alloys Research Articles

Interface‐Induced Anomalous Behavior of Magnetism in FexGeTe2/Pt Bilayer

AbstractInterface engineering is a promising strategy for controlling the Curie temperature (Tc) and perpendicular magnetic anisotropy (PMA) in magnetic 2D van der Waals (2D vdWs)‐based heterostructures. However, establishing high‐quality interface structures in magnetic 2D vdWs/metal stacks, crucial for maximizing interface effects, remains a significant challenge. Here, a Fe5‐xGeTe2/Pt (F5GT/Pt) prototype with a superior interface quality is achieved using a low‐power physical vapor deposition technique. The magnetic properties of the F5GT/Pt heterostructures are strongly influenced by employing the specific physical deposition method. Stable ferromagnetism at 400 K is observed when depositing Pt atoms with relatively high energy, despite the Tc of pristine F5GT being below 300 K. This unexpected high‐temperature ferromagnetism is attributed to the formation of a ferromagnetic alloy at the interface, commonly present in vdWs‐based stacks fabricated through physical deposition but often overlooked. The deposit of Pt atoms with ultralow energy leads to the formation of a unique Fe5‐xGeTe2/Fe3‐xGeTe2 heterojunction at the interface, significantly enhancing the PMA. This work emphasizes the importance of interface structures in vdWs‐based devices, suggesting that controlling the growth process offers an effective approach to construct and engineer vdWs heterostructures, thus improving the performance and introducing new functionalities to spintronic devices.

Exploring Broadband Electromagnetic Absorption Characteristics and Composition Optimization in Novel Synthesized Ni2Fe1+xGe1−x Alloy Powders

This study reports for the first time the successful synthesis of a novel series of Ni2Fe1+xGe1−x (x = 0.25, 0.50, 0.75, 0.90) polycrystalline alloy materials with L21 austenite structure using the mechanical alloying method. Notably, the Ni2Fe1+xGe1−x alloys demonstrate excellent electromagnetic wave absorption performance across the entire 2–18 GHz frequency range, and by adjusting the composition ratio of iron and germanium, it is possible to effectively regulate their complex permittivity () and permeability (), thereby adjusting the reflection loss. All Ni2Fe1+xGe1−x samples show an effective electromagnetic wave absorption effect of more than −10 dB, indicating that 90% of the electromagnetic waves are efficiently absorbed. Among them, the Ni2Fe1.5Ge0.5 sample achieves an outstanding −43.5 dB reflection loss at 3.2 GHz, and the maximum effective absorption bandwidth reaches 5.8 GHz (11.8–17.6 GHz) with just a 1.6 mm thickness, fully covering the Ku band. This excellent absorption ability comes from the strong ability of the material to reduce signal strength and its perfect impedance matching. This study first shows the high potential of Ni2Fe1+xGe1−x ferromagnetic alloys as effective, wide‐range electromagnetic wave absorbers. It suggests the ferromagnetic Ni2Fe1+xGe1−x alloys hold promise as appealing candidates for broadband and high‐efficiency electromagnetic wave absorption.

Magneto-mechanical hysteresis damping mechanism in dual-phase iron-based alloy with zero magnetostriction

Magneto-mechanical hysteresis damping (MMHD) is usually positively correlated with their measured magnetostriction, but this correlation becomes ambiguous in negative magnetostriction and multiphase materials. This work found that even if saturated magnetostriction of Co-20Fe alloy is zero, its MMHD value can still be as high as 0.015. Analysis revealed that the MMHD correlates with phase percentages and the absolute parallel magnetostriction values of phases. In multiphase alloys, measured magnetostriction cannot be directly used to assess damping. High nonmagnetic damping in Co-15Fe alloy with fcc structure is due to distributed misfit dislocations. This research sheds light on damping mechanisms in multiphase ferromagnetic alloys.

First-principles study of stability, order and disorder based on an entropy descriptor in noble and ferromagnetic transition metal alloys

Binary alloys AB composed of ferromagnetic metals A (Fe, Co, Ni) and the late 4d−5d noble metals B (Rh, Pd, Ag, Ir, Pt, Au) have been investigated using density functional theory with the generalized gradient approximation to understand the role of magnetism in the stability and the order–disorder transition which has an impact on their physicochemical properties, their applications and their possible implementation as precursors of high-entropy alloys. The enthalpy of formation related to the stability demonstrates that all the alloys are more stable in the ferromagnetic phase than in the nonmagnetic phase. The transition from ordered to disordered phases is quantified using a descriptor which is the standard deviation of the energy spectrum of a set of small nanoalloys with random atomic configurations. The study highlights the fact that the entropy-related descriptor, which is a quantity in determining the formation of a disordered phase as a solid solution or an ordered phase is highly dependent on the atomic environment. Despite the fact that the overall variation of this descriptor is supposed to be unpredictable, there is a noticeable trend showing that the environment-dependent ferromagnetism contributes to a chemical order in alloys and nanoalloys and that this order depends on the atomic radius of the species considered. The results indicate that species with small atomic radii, such as nickel, rhodium or iridium are more likely to form solid solutions than species with larger atomic radii and with more delocalized orbitals.

Integration of Sm2Co17 Micromagnets in a Ferromagnetic Multipolar Microrotor to Enhance MEMS and Micromotor Performance.

MEMS and micromotors may benefit from the increasing complexity of rotors by integrating a larger number of magnetic dipoles. In this article, a new microassembly and bonding process to integrate multiple Sm2Co17 micromagnets in a ferromagnetic core is presented. We experimentally demonstrate the feasibility of a multipolar micrometric magnetic rotor with 11 magnetic dipoles made of N35 Sm2Co17 micromagnets (length below 250 μm and thickness of 65 μm), integrated on a ferromagnetic core. We explain the micromanufacturing methods and the multistep microassembly process. The core is manufactured on ferromagnetic alloy Fe49Co49V2 and has an external diameter of 800 μm and a thickness of 200 μm. Magnetic and geometric measurements show good geometric fitting and planarity. The manufactured microrotor also shows good agreement among the magnetic measurements and the magnetic simulations which means that there is no magnetic degradation of the permanent magnet during the manufacturing and assembly process. This technique enables new design possibilities to significantly increase the performance of micromotors or MEMS.

Magnetic behavior of 3D interconnect nanoporous FeCo synthesized by liquid metal dealloying

Liquid Metal Dealloying (LMD) is tested to enhance the near-surface magnetic properties of ferromagnetic Iron-Cobalt alloys. With a lower surface electrical conductivity, treated specimens are expected to accommodate the frequency effect better and exhibit a lower level of magnetic loss. This work focuses on the magnetic viability of LMD-treated samples. The magnetic hysteresis cycles of virgin, fully-dealloyed, and partially-dealloyed specimens are measured from quasi-static to dynamic regimes. For each category of specimens, experimental results are compared with numerical predictions given by dedicated hysteresis models. The simulation parameters of the fully-dealloyed and the virgin specimens are leveraged to predict the partially-dealloyed specimen's behavior and estimate the thickness of the treated area accurately and non-destructively. Together with SEM observations and finite element simulations, these results show that the magnetic behavior of the metallic part in the dealloyed layer is barely affected by the specimen porosity, but the average variations observed experimentally are primarily due to the distortion of the magnetic lines and changes in the local geometry.

An approach to describe the twinning and detwinning processes of the martensitic structure in ferromagnetic alloy with shape memory in magnetic and force fields

In the article, based on the theory of micromagnetism, a special case of the moment theory of elasticity for an anisotropic material and the Hadamard compatibility condition for deformations, a microstructural model of the behavior of the Heusler alloy with shape memory in magnetic and force fields is constructed. The dynamics of the magnetic process is described by the Landau-Lifshitz-Gilbert equation. Using the Galerkin procedure, variational equations corresponding to the differential relations of the magnetic problem are written out and the finite element method is used for numerical realization of these equations. Considering the problems of the moment theory of elasticity we come to a special case of this theory in which, under the action of force and magnetic fields, the tensor of moment stresses initiated only by the magnetic field is zero. Using this result, the general expression for the state equation is constructed that describes, within the framework of small deformations, the behavior of an anisotropic material under force and magnetic influences. The stress tensor in this equation consists of a symmetric part and a skew-symmetric part, depending only on the magnetic field. For the problem of deformable solid mechanics with such a state equation, the Lagrange variational equation was constructed, which made it possible to reduce the requirements for the smoothness of the desired solution by an order of magnitude. The general expression for the state equation has been concretized for an anisotropic material having one axis of symmetry of the fourth order and two axes of symmetry of the second order. The solution of the Hadamard compatibility equation for deformations made it possible to determine the sliding surfaces and sliding directions in a tetragonal crystal cell of a ferromagnetic material in the martensitic state, along which a shift occurs, leading to the appearance and dissipation of a twinned structure. The microstructural model, constructed using all these positions, is used to describe experimental results on the combined action of magnetic and force fields on the Heusler alloy.

Binary and ternary ferromagnetic alloy/C nanocapsules for improved X-band microwave absorption

The dielectric-magnetic matching effect emerges from the presence of dual dielectric relaxation and multiple magnetic resonances. This phenomenon becomes a strategic approach in the quest to enhance microwave absorption performance by optimizing magnetic components. Herein, binary and ternary ferromagnetic alloy with tunable components embedded in carbon skeleton (core/shell) nanocapsules has been successfully fabricated by one step metal-organic chemical vapor deposition. The core/shell structure design introduces numerous interfaces that amplify dielectric loss stemming from polarization. It is important to emphasize that modifying the composition of magnetic core in these nanocapsules effectively regulates the impedance matching characteristics. As a result, the CoFeNi/C nanocapsules demonstrate an optimal reflection loss (RLmin) of −53.6 dB at a thickness of 2.55 mm, alongside an effective absorption bandwidth of 5.92 GHz at a thickness of 2.05 mm, with a filling ratio as low as 20 wt%. This study has provided valuable insights into a promising avenue for fabricating dielectric-magnetic nanocomposites with outstanding microwave attenuation capabilities through the manipulation of composited elements.

Development of instruments for imaging of local magnetic structure by magnetic neutron holography

We have developed instruments for magnetic neutron holography (MNH) using polarized white neutrons to investigate the local magnetic structures of magnetic alloys. We chose the 3He spin filter method as the neutron polarizer to polarize neutrons over a wide wavelength range of up to a few 100 meV. We developed a magnet device to saturate the magnetizations of ferromagnetic samples, and instruments to transport polarized neutrons from a 3He spin filter to the MNH sample. The neutron polarization, Pn, at the beginning of the MNH experiments was confirmed to be 0.46, which is feasible for MNH. Using the developed instruments, we obtained preliminary results for the room-temperature ferromagnetic alloy Fe0.08Co0.92. Technical problems encountered in the experiments and ways to overcome them are discussed. Based on these results, we believe that MNH that use polarized neutrons is promising.

Superior microwave absorption properties of carbon-coated FeSiCr micro flakes

Carbon-coated ferromagnetic alloys can protect from microwave radiation due to their tunable electromagnetic parameters and multiple loss mechanisms. We prepared carbon-coated flaky FeSiCr (FFSC@C) powders by the encapsulation and thermal decomposition of epoxy resin. The crystallization degree and thickness of carbon coating were tuned to optimize the microwave absorption of FFSC@C. The phase composition, morphology, magnetic properties, electromagnetic parameters, and microwave absorption properties of FFSC@C were comprehensively investigated. The oriented flaky FeSiCr possessed strong attenuation capacity, the amorphous carbon improved the impedance matching of flaky FeSiCr. The sample carbonized at 500 ℃, with the epoxy addition amount of 45 wt% exhibited a broad effective absorption bandwidth of 5.60 GHz at a thickness of 2.4 mm. Compared with other absorbents, the FFSC@C exhibited stronger absorption capacity at a lower thickness and filler loading in the X-band (8−12 GHz). This work demonstrated the facile fabrication of a high-performance carbon-coated ferromagnetic microwave absorber.

Thickness-Dependent Gilbert Damping and Soft Magnetism in Metal/Co-Fe-B/Metal Sandwich Structure.

The achievement of the low Gilbert damping parameter in spin dynamic modulation is attractive for spintronic devices with low energy consumption and high speed. Metallic ferromagnetic alloy Co-Fe-B is a possible candidate due to its high compatibility with spintronic technologies. Here, we report thickness-dependent damping and soft magnetism in Co-Fe-B films sandwiched between two non-magnetic layers with Co-Fe-B films up to 50 nm thick. A non-monotonic variation of Co-Fe-B film damping with thickness is observed, which is in contrast to previously reported monotonic trends. The minimum damping and the corresponding Co-Fe-B thickness vary significantly among the different non-magnetic layer series, indicating that the structure selection significantly alters the relative contributions of various damping mechanisms. Thus, we developed a quantitative method to distinguish intrinsic from extrinsic damping via ferromagnetic resonance measurements of thickness-dependent damping rather than the traditional numerical calculation method. By separating extrinsic and intrinsic damping, each mechanism affecting the total damping of Co-Fe-B films in sandwich structures is analyzed in detail. Our findings have revealed that the thickness-dependent damping measurement is an effective tool for quantitatively investigating different damping mechanisms. This investigation provides an understanding of underlying mechanisms and opens up avenues for achieving low damping in Co-Fe-B alloy film, which is beneficial for the applications in spintronic devices design and optimization.

Tunability of Microwave Frequency Using Spin Torque Nano Oscillator by the Generated Oersted Field with Tunable Free Layer

The current-induced magnetization precession dynamics provoked by the spin transfer torque (STT) in a spin valve device i.e. tri-layer device (commonly spin torque nano oscillator (STNO)) is investigated numerically by solving the governing Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. In this study, we have devised an STNO device made of EuO-based ferromagnetic alloy in free and fixed magnetic layers. The copper acts as a nonmagnetic spacer. Here, we have introduced the current induced Oesterd field (CIOF), which is generated when a spin-polarized current passes through the STNO device. In the device, we have tuned the free layer angle [Formula: see text] from [Formula: see text] to [Formula: see text] as an increment of [Formula: see text]. For every individual [Formula: see text] ranging from [Formula: see text] to [Formula: see text], the generated Oersted field’s strength can be altered by increasing the STNO device’s diameter. Henceforth, it is apparent that the frequency tunability is achieved in the device for all the values of [Formula: see text]. The frequency and power of the device depend entirely on the material’s saturation magnetization, which inherently reflects the current density and coherence of spin-polarized DC. From the results, it is apparent that for a particular [Formula: see text], the frequency keeps increasing with the eventual decrease in power when we increase the strength of the Oersted field from 10[Formula: see text]kA/m to 50[Formula: see text]kA/m. By doing so, the maximum frequency can be tuned up to 212[Formula: see text]GHz for [Formula: see text] with [Formula: see text] as 50[Formula: see text]kA/m. The high frequency emitted by the device acts as a linchpin ingredient, as well as a launch pad element in much of scientific and technological point of view. It paves way for a new route in the areas such as high capacity, high precision, high density as well as the sensing applications.

Coexisting magnetic interaction, critical behavior and magnetocaloric effect at high temperature in Fe50Ni50 soft ferromagnetic alloy

Herein, we report the structural, magnetic and magnetocaloric properties of Fe50Ni50 alloy prepared through the planetary ball-mill. Rietveld analysis of the X-ray profiles confirmed the cubic crystallographic phase with the Fm-3 m space group. The magnetic characterization demonstrates that Fe50Ni50 alloy exhibits the coexistence of magnetic interaction within the ferromagnetic phase with Curie temperature 762 K. The Arrott plot results confirmed the second-order nature of the alloy. Critical exponents were also determined using the modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis. Obtained results indicated coexisting magnetic behavior, i.e., long-range ferromagnetism and inhomogeneous magnetic state. This alloy also noted a significant magnetocaloric parameters, i.e., magnetic entropy change (−ΔSM ∼ 2.3 J/kg-K) and relative cooling power (RCP ∼ 230 J/kg) at 30 kOe applied field. Both parameters followed power law dependence of magnetic field, and the exponent value supports the ferromagnetic nature along with the coexisting magnetic state. By normalizing the ΔSM curve with rescaled temperature, a universal master curve is also constructed for this alloy, reiterating the second-order nature of the magnetic transition.

Effect of uniaxial strain on the electronic and magnetic properties of N2SrRb: a DFT study

ABSTRACT Using the first-principles density functional theory calculations, we examined the effect of uniaxial strain on the electronic and magnetic properties of full-Heusler alloy N2SrRb. Our results show that N2SrRb is a ferromagnetic full-Heusler alloy, and it exhibits half metallic properties with 100% spin polarisation when no strain is applied. The half-metallic and magnetic properties of N2SrRb were retained under the ranges of tensile and compressive strain applied. The spin flip gap was found to increase as the tensile strain increases, while it decreases as the compressive strain increases. The mechanical properties show that the full-Heusler alloy is mechanically stable and having a ductile characteristics

High-strength corrosion-resistant FeMnCr-based composite damping alloys fabricated by vacuum annealing

High-strength high manganese FeMn-based damping alloys suffer from lower damping capacity at low strain amplitudes and poor corrosion resistance, while the strength is lower in stainless ferromagnetic FeCr-based alloys with high damping capacity at low strain amplitudes. By simple vacuum annealing, we fabricated high-strength, high-manganese FeMnCr-based alloys coated with ferromagnetic FeCr-based stainless damping alloys. Compared to the FeMn-based alloys, the FeMnCr-based composite alloys showed not only higher damping capacity at low strain amplitudes and higher tensile strength but also much better corrosion resistance. Stress relief annealing could further improve their damping capacity. The vacuum annealing will offer a new technique for fabricating composite alloys with unique properties.

Investigation of deterministic and cumulative nature in helicity-dependent optical switching of ferrimagnetic Gd–Fe–Co films

The precise control of magnetization using circularly polarized laser pulses in perpendicularly magnetized films is a key approach to develop storage media. Although deterministic helicity-dependent magnetization switching (HDMS) in a single-pulse excitation has been observed in ferrimagnetic Gd–Fe–Co alloys, ferromagnetic [Co/Pt]N multilayers require cumulative effects of multiple pulses to achieve HDMS. In this study, we systematically investigated the single-shot and cumulative nature of HDMS using ferrimagnetic Gd–Fe–Co films with varying compositions and multilayer structures, in terms of angular momentum compensation, thermal diffusion, mobility of domain walls, and the size of the magneto-optical effect. These results provide insights for the realization of single-shot HDMS in various magnetic systems, such as ferromagnetic alloys.

Study of magnetic nonlinearities in materials with low Curie temperature applied to domestic induction heating

The analysis of the magnetic properties of alloys with low Curie temperature used in domestic induction heating is presented. These alloys allow the development of cookware with additional benefits with respect to regular cookware oriented to improve temperature control and the user’s safety. Firstly, an experimental method to characterize the magnetic permeability with respect to the magnetic field strength and temperature in the material is presented. Secondly, a finite element simulation method is proposed which, considering the previous characterization, allows the calculation of the electrical equivalent of an inductor-load system as a function of temperature and magnetic field. This method makes possible the application of finite element simulation in the frequency domain with nonlinear materials, which is of interest for the design of electronics associated with domestic applications of induction heating. Simulation results are experimentally verified with various ferromagnetic alloys with low Curie temperature at different power, temperature, and operating frequency ranges.

Emergent half-metal with mixed structural order in (111)-oriented (LaMnO3)2n|(SrMnO3)n superlattices

Using first-principles techniques, we study the structural, magnetic, and electronic properties of (111)-oriented (LaMnO3)2n|(SrMnO3)n superlattices of varying thickness (n=2,4,6). We find that the properties of the thinnest superlattice (n=2) are similar to the celebrated half-metallic ferromagnetic alloy La2/3Sr1/3MnO3, with quenched Jahn-Teller distortions. At intermediate thickness (n=4), the a−a−a− tilting pattern transitions to the a−a−c+ tilting pattern, driven by the lattice degrees of freedom in the LaMnO3 region. The emergence of the Jahn-Teller modes and the spatial extent needed for their development play a key role in this structural transition. For the largest thickness considered (n=6), we unveil an emergent separation of Jahn-Teller and volume-breathing orders in the ground-state structure with the a−a−c+ tilting pattern, whereas it vanishes in the antiferromagnetic configurations. The ground state of all superlattices is half-metallic ferromagnetic, not affected by the underlying series of structural transitions. Overall, these results outline a thickness-induced crossover between the physical properties of bulk La2/3Sr1/3MnO3 and bulk LaMnO3. Published by the American Physical Society 2024

Tuning ultrafast demagnetization dynamics in FePdPt ternary alloy films: the role of spin–orbit coupling

The influence of spin–orbit coupling (SOC) on ultrafast demagnetization dynamics is still an obscure issue. Ferromagnetic ternary alloy film containing Platinum element has the advantage that SOC strength can be regulated flexibly by varying the component ratio, thus is an excellent platform for investigating the dynamical effect of SOC. Here the fluence and component dependences of ultrafast demagnetization dynamics in ternary alloy L10-Fe0.5(Pd1-xPtx)0.5 films are studied by using time-resolved magneto-optical Kerr spectroscopy. An excitation-fluence dependent transition of demagnetization dynamics shows the Elliott-Yafet (EY) spin-flip scattering as the dominant mechanism of ultrafast demagnetization. We analyze the dynamics by a compatible fitting model and extract multiple characteristic time constants. It is clearly demonstrated that the gradual enhancement of SOC in fact decreases the spin-flip scattering and slow down the demagnetization process. We further show that the demagnetization time τm scales with the SOC strength ξ approximately under a dependence of τm∝ξ1/3, while a linear dependence exists between the spin–lattice relaxation time τs-l and ξ-6. These findings clarify the role of SOC in EY-dominated demagnetization dynamics and demonstrate an approach for tuning the speeds and duration of ultrafast demagnetization by regulating SOC strength.

Promoting electrocatalytic nitrogen reduction by introducing low-spin sites in ferromagnetic single-atom alloys

In ferromagnetic single-atom alloys, the average electron spin moment P of dopants, a new descriptor, has volcano relationships with the e-NRR theoretical activity and selectivity.