Search Results (237)

In this study, we investigate the dominant electromagnetic wave absorption mechanism–ferromagnetic resonance (FMR) loss versus quarter-wave cancellation in a novel PVDF-based polymer composite embedded with carbonaceous nanostructures incorporating FeCoCr ternary alloy. The majority of the nanoparticles are embedded at the terminal ends of the carbon nanotubes, while a small fraction exists as isolated core–shell, carbon-coated spherical particles. Overall, the synthesized material predominantly exhibits a nanotubular carbon morphology. High-resolution transmission electron microscopy (HRTEM) confirms that the encapsulated nanoparticles are quasi-spherical in shape, with an average size ranging from approximately 25 to 40 nm. The polymeric composite was synthesized via solution casting, ensuring homogenous dispersion of filler constituent. Electromagnetic interference (EMI) shielding performance and reflection loss characteristics were evaluated in the X-band frequency range. Experimental results reveal a significant reflection loss exceeding −20 dB at a matching thickness of 2.5 mm, with peak absorption shifting across frequencies with thickness variation. The comparative analysis, supported by quarter-wave theory and FMR resonance conditions, indicates that the absorption mechanism transitions between magnetic resonance and interference-based cancellation depending on the material configuration and thickness. This work provides experimental validation of loss mechanism dominance in magnetic alloy/polymer composites and proposes design principles for tailoring broadband microwave absorbers. Full article

To our knowledge, no magnetic B2 phase in the Al–Mn system of near-equiatomic compositions has been reported so far. Here, we investigate the structural and magnetic characteristics of Al₄₅Mn_41.8X_13.2 (X = Fe, Co or Ni) alloys. We demonstrate that adding 13.2 atomic percent magnetic 3d metal to AlMn stabilizes a ferromagnetic B2 structure, where Al and X occupy different sublattices. We employ density functional theory calculations and experimental characterizations to underscore the role of the late 3d metals for the phase stability of the quasi-ordered ternary systems. We show that these alloys possess large local magnetic moments primarily due to Mn atoms partitioned to the Al-free sublattice. The revealed magneto-chemical effect opens alternative routes for tailoring the magnetic properties of B2 intermetallic compounds for various magnetic applications. Full article

The growing demand for rare-earth magnets has raised concerns over their price and the country’s risk of depleting the supply of rare-earth elements. These severe concerns have led to the study of rare-earth-free magnets that do not rely on rare-earth elements. Co-Zr-Mo-B alloys, one of the prospective candidates for rare-earth-free magnets, were produced by the melt-spinning technique and subsequent annealing. It was found that a small substitution of Mo for Zr in the Co-Zr-B alloys increased coercivity. The Co-Zr-Mo-B alloy with a Mo content of 2 at% showed a high coercivity of 6.2 kOe with a remanence of 40 emu/g. SEM studies showed that the annealed Co-Zr-Mo-B alloys had fine, uniform grains with an average diameter of about 0.6 μm. Further studies using STEM demonstrated that the ferromagnetic phase in the annealed Co-Zr-Mo-B alloys with high coercivity was composed of the Co₅Zr phase and the long-period stacking ordered (LPSO) phase. That is, the fine grains observed in the SEM studies were found to be ferromagnetic dendrites containing numerous twin boundaries of the Co₅Zr phase and its derived LPSO phase. Therefore, the high coercivity of the Co-Zr-Mo-B alloys can be attributed to the presence of ferromagnetic crystals of Co₅Zr and the derived LPSO phase. Full article

Recent achievements in ultrafast spin physics have enabled the use of heterostructures composed of ferromagnetic (FM)/non-magnetic (NM) thin layers for terahertz (THz) generation. The mechanism of THz emission from FM/NM multilayers has been typically ascribed to the inverse spin Hall effect (ISHE). In this work, we probe the mechanism of the ISHE by inserting a second ferromagnetic layer in the form of an alloy between the FM/NM system. In particular, by utilizing the co-sputtering technique, we fabricate Fe/L1₀-FePt/Pt ultra-thin heterostructures. We successfully grow the tetragonal phase of FePt (L1₀-phase) as revealed by X-ray diffraction and reflection techniques. We show the strong magnetic coupling between Fe and L1₀-FePt using magneto-optical and Superconducting Quantum Interference Device (SQUID) magnetometry. Subsequently, by utilizing THz time domain spectroscopy technique, we record the THz emission and thus we the reveal the efficiency of spin-to-charge conversion in Fe/L1₀-FePt/Pt. We establish that Fe/L1₀-FePt/Pt configuration is significantly superior to the Fe/Pt bilayer structure, regarding THz emission amplitude. The unique trilayer structure opens new perspectives in terms of material choices for the future spintronic THz sources. Full article

The effect of severe plastic deformation during milling and conventional and Spark Plasma Sintering (SPS) on the wt. % microstructural, structural, thermal, magnetic, and mechanical properties of the Al–16 wt. % Mn–7 wt. % Cu alloy was studied. A milling process for up to 24 h (A24) leads to microstructure refinement and the presence of Al, Mn, and Cu solid solutions. The energy dispersive spectroscopy (EDS) analysis reveals the existence of Cu–Al, Mn–Al, and Al–Mn enriched particles. The powders exhibit weak ferromagnetism and an exchange bias (EB) behaviour that decreases with increasing milling time. The Ms values fitted using the law of approach to saturation (LAS) are comparable to the experimental values. The exothermic and endothermic peaks that appear in the differential scanning calorimetry (DSC) scans in the 500–900 °C range on heating/cooling are related to different phase transformations. The crystal structure of the A24 powders heated up to 900 °C (A24_900 °C) consists of a dual-phase microstructure of Al₂₀Cu₂Mn₃ nanoprecipitates (~28%) and Al matrix (~72%). The sintering of the A24 powders at 500 °C for one hour (A24S) leads to the precipitation of Al₆Mn, Al₂Cu, and the Al₂₀Cu₂Mn₃ T-phase into the Al-enriched matrix. In contrast, the consolidation by SPS (A24SPS) leads to a mixture of an Al solid solution, Al₆Mn, T-phase, and α-Mn with an increased weight fraction of the T-phase and Al₆Mn. The sintered samples exhibit the coexistence of a significant PM/AFM contribution to the M-H curves, with increasing Hc and decreasing EB. A higher microhardness value of about 581 HV is achieved for the A24SPS sample compared to those of the A24 (68 HV) and A24S (80 HV) samples. Full article

This study employs DFT+U calculations to investigate the ferromagnetic properties of ErAl₂ and ErNi₂ Laves phases under an external hydrostatic pressure P (0 GPa ≤ P ≤ 1.0 GPa). The calculated magnetic moments per formula unit for both crystalline structures align with experimentally reported values: 4.40 μ_B/f.u. in the hard magnetization <001> axis for ErAl₂ and 5.56 μ_B/f.u. in the easy magnetization <001> axis for ErNi₂. The DFT results indicate that the magnetic moment remains unchanged up to 1 GPa of hydrostatic pressure, with no structural instabilities observed, as evidenced by a nearly constant formation energy for ErAl₂ and ErNi₂ alloys. The simulations confirm that the magnetic behavior of ErAl₂ is primarily driven by the electrons localized in the f orbitals. In contrast, for ErNi₂, both d and f orbitals significantly contribute to the total magnetic moment. Finally, the electronic specific heat coefficient was calculated and reported as a function of hydrostatic pressure up to P = 1.0 GPa for each Laves phase. Full article

This study explores the crystal structure, microstructure and magnetic phase evolution of the AlCoCrFeNi high-entropy alloy (HEA), highlighting its potential for applications requiring tailored magnetic properties across diverse temperatures. Electron microscopy and X-ray diffraction revealed that the as-cast alloy’s microstructure comprises equiaxed grains with branching dendrites, showing compositional variations between interdendritic regions enriched in Al and Ni. Temperature-induced phase transformations were observed above room temperature, transitioning from body centered cubic (BCC) phases (A2 and B2) to a predominant FCC phase at higher temperatures, followed by recrystallization of the A2 phase upon cooling. Magnetization measurements showed a drop near 380 K, suggesting the Curie temperature of BCC phases, a peak at 830 K attributed to optimal magnetic alignment in the FCC phase, and a sharp decline at 950 K marking the transition to a paramagnetic state. Magnetic moment calculations provided insights into magnetic alignment dynamics, while low-temperature analysis highlighted the alloy’s magnetically soft nature, dominated by ferromagnetic contributions from the A2 phase. These findings underscore the strong interdependence of microstructural features and magnetic behavior, offering a foundation for optimizing HEAs for temperature-sensitive scientific and industrial applications. Full article

First-principles calculations were carried out to investigate the physical properties of the full-Heusler compound In₂MnW. The WIEN2K code was utilized with various approximations, such as GGA and GGA+U, to analyze its structural, electronic, and magnetic properties. The unit cell was optimized to determine the ground-state energy. The calculated formation enthalpy (ΔH) of In₂MnW is −0.189 eV, indicating its thermodynamic stability due to the negative value. Band structure analysis using both potentials confirms the compound’s metallic nature, which is further supported by total density of states calculations. The total magnetic moment is found to be 4.3 µB, which slightly increases to 4.4 µB when the U parameter is included. These findings suggest that In₂MnW demonstrates metallic ferromagnetic behavior, highlighting its potential as a promising ferromagnetic material for mass storage applications. Full article

Based on modern concepts of the nonlinear percolation mechanisms of electrical and magnetic properties in granular metal–dielectric nanocomposites, the authors present for the first time a comparative analysis of their own results of a comprehensive study of nonlinear electromagnetic properties in two nanocomposite systems: metal–dielectric Co_x(MgF₂)_100−x and alloy–dielectric (CoFeZr)_x(MgF₂)_100−x, obtained by ion-beam sputtering of composite targets in a wide range of different compositions. For the first time, the features of the influence of atomic composition and structural-phase transitions on nonlinear magnetoresistive, magnetic, and magneto-optical properties in two systems are presented in comparison, one of which, Co_x(MgF₂)_100−x, showed soft magnetic properties, and the second, (CoFeZr)_x(MgF₂)_100−x, hard magnetic properties, during the transition from the superparamagnetic to the ferromagnetic state. Moreover, for the first time, the concentration dependences of the oscillating fine structure of XANES K-absorption edges of Co atoms in the first system and Co and Fe atoms in the second system are presented, which undergo changes at the percolation thresholds in each of the two systems and thus confirm the nonlinear nature of the electromagnetic properties changes in each of the two systems at the atomic level. Full article

The full Heusler alloys Ni₂MnZ (Z = In, Sn, Sb) exhibit ferromagnetic properties with a Curie temperature (T_C) above room temperature. The magnetic properties of Ni₂MnZ (Z = In, Sn, Sb) were studied through a combination of experiments and band calculations under ambient and elevated pressures. The main results of this study open up further prospects for controlling the magnetic properties of the multifunctional Heusler alloys Ni₂Mn_1+xZ_1−x (Z = In, Sn, Sb) and their practical application. Full article

Recently, a new phase, ω–Fe, has been observed in martensitic substructures, providing a new path for studying the position and evolution of nitrogen in high-nitrogen steels. In this paper, the density functional method was used to investigate the thermodynamic and dynamic stability of N atoms in the phases of ω–Fe, α–Fe, and γ–Fe in martensite, as well as the influence of magnetic order on them. The calculated results show that in the pure Fe phases, ferromagnetic α–Fe is a stable phase both in thermodynamics and dynamics. ω–Fe and γ–Fe are most stable in ferrimagnetism and show dynamic stability, while in ferromagnetic state they are unstable in both thermodynamics and dynamics. N-atom doping of 25% (Fe₃N) makes γ–Fe and ω–Fe thermodynamically and dynamically stable in ferromagnetic state. However, a higher N content is not conducive to the stability of ω–Fe and γ–Fe. The electronic structure shows that as the content of N atoms becomes higher than 25%, the 2p orbitals of N atoms move towards the Fermi level and become more dispersed, resulting in a large contribution of the density of states at the Fermi level. In addition, N atoms are not conducive to the stability of α–Fe, as they relax to the structure of γ–Fe at 25% N content (Fe₃N), while α–Fe in higher N contents (Fe₃N₂ and FeN) relaxes to the structure of ω–Fe correspondingly. Obviously, N tends to stabilize in the ω and γ phases in martensite, and our study provides a new clue for the formation mechanism of nitrides and martensitic transformation in Fe–N alloys. Full article

The development of high-performance and cost-effective Nd-Fe-B permanent magnets is crucial to meet the ever-growing requirements of renewable and clean energy applications. Here, we use low-cost and highly abundant La and Ce to partially substitute Nd and investigate the effect of annealing treatment with a 1 tesla (T) magnetic field on the microstructures and magnetic properties of (Nd_0.8RE_0.2)_2.2Fe₁₂Co₂B (RE = La, Ce) ribbons. The remanence (B_r) and maximum energy product ((BH)_max) of studied alloys can be improved by magnetic field annealing. The respective B_r and (BH)_max of annealed (Nd_0.8La_0.2)_2.2Fe₁₂Co₂B alloy are increased to 0.86 T and 124 kJ/m³. In comparison to melt-spun (Nd_0.8Ce_0.2)_2.2Fe₁₂Co₂B alloy, the B_r and (BH)_max of the magnetic field-annealed alloy are improved by 5% and 8%. The underlying mechanism of improved magnetic properties of La- and Ce-substituted alloys is different. The interaction magnetic domain size in (Nd_0.8La_0.2)_2.2Fe₁₂Co₂B alloy can be increased by magnetic field annealing, leading to the enhancement of exchange coupling interaction, which results to the improvement in B_r and (BH)_max. In the (Nd_0.8Ce_0.2)_2.2Fe₁₂Co₂B alloy, the concentration of (Fe + Co) of ferromagnetic intergranular phase is increased after magnetic field annealing, resulting in the increase in B_r and (BH)_max. Full article

We explored the potential for an aging treatment to achieve high coercivity, of 0.859 MA/m, in a SmFe₁₀V₂ alloy with a ThMn₁₂-type structure. Bulk magnets were fabricated by sintering ball-milled powders, followed by aging treatment. XRD and SEM analyses revealed that aging treatment promotes the formation of a Sm-rich grain boundary phase with nano-scale thickness. The high Sm content (~60–80 at.%) and low Fe content (~20–30 at.%) in the grain boundary phase led to non-ferromagnetism, enhancing the coercivity by isolating the 1–12 grains and weakening the dipolar interaction between the grains. The aging temperature and duration were optimized to maximize the Sm-rich phase and minimize the soft magnetic SmFe₂ phase. This study provides a new fabrication method for ThMn₁₂-type magnets and investigates the relationship between microstructure and coercivity, offering valuable insights for the future design and development of high-performance SmFe₁₂-based magnets. Full article

The high damping alloy materials, by virtue of the excellent mechanical properties and damping performance generated by the material’s properties and internal friction mechanism, can be employed directly in the reduction of structural vibrations. On the basis of summarising the current research progress and application status of existing damping alloy materials, the damping characteristics of Fe-12Cr-3Al ferromagnetic high damping alloy material were tested and applied to the vibration reduction of an aero-engine lubricating oil tank. Subsequent to this, vibration characteristics simulation analysis and tests were conducted. The results show that the amplitude reduction rate of mounting structures utilising the Fe-12Cr-3Al ferromagnetic high damping alloy is 30% in comparison to Q235 carbon steel. Additionally, the vibration transmission rate can be diminished by 40%. The utilisation of the Fe-12Cr-3Al ferromagnetic high damping alloy in the aero-engine mounting structure has been observed to result in a discernible reduction in vibration. Full article

The impact of the interface phenomena on the properties of nanostructured materials is the focus of modern physics. We studied the magnetic properties of the nanostructured In–Ag alloy confined within a porous glass. The alloy composition was close to the eutectic point in the indium-rich range of the phase diagram. Temperature dependences of DC magnetization evidenced two superconducting transitions at 4.05 and 3.38 K. The magnetization isotherms demonstrated the superposition of two hysteresis loops with low and high critical fields below the second transition, a single hysteresis between the transitions and ferromagnetism with weak remanence in the normal state of the alloy. The shape of the loop seen below the second transition, which closes at a low magnetic field, corresponded to the intermediate state of the type-I superconductor. It was ascribed to strongly linked indium segregates. The loop observed below the first transition is referred to as type-II superconductivity. The secondary and tertiary magnetization branches measured at decreasing and increasing fields were shifted relative to each other, revealing the proximity of superconducting and ferromagnetic phases at the nanometer scale. This phenomenon was observed for the first time in the alloy, whose components were not magnetic in bulk. The sign of the shift shows the dominant role of the stray fields of ferromagnetic regions. Ferromagnetism was suggested to emerge at the interface between the In and AgIn₂ segregates. Full article