Optimization of structural,electrical, and magnetic properties of ytterbium substituted W-type hexaferrite for multi-layer chip inductors

The rare earth (Yb³⁺) substituted W-type hexagonal ferrites with composition CaPb_2-xYb_xFe₁₆O₂₇ (x = 0.0, 0.5, 1.0, 1.5, 2.0) were synthesized by a facile and cost-effective sol-gel auto combustion method with post heat treatment. The synthesized hexagonal ferrites were characterized by a variety of analytical techniques, and an impedance analyzer was used to investigate the effects of Ytterbium on structural, magnetic, spectral and dielectric properties. The relationship between their impedance, structure and dielectric properties was investigated. The X-ray diffraction patterns verify the presence of single-phase W-type hexagonal ferrites. Physical properties such as D_bulk (bulk density), D_xrd (X-ray density), and P (porosity) of the CaPb_2-xYb_xFe₁₆O₂₇ W-type hexagonal ferrites were calculated. The bulk density of all the samples was decreased, and X-ray intensity was increased with the Ytterbium replacement in the W-type hexaferrite. By adding Yb³⁺ ions, the lattice parameters, cell volume and X-ray density were reduced due to the substitution of ytterbium with smaller ionic radii compared to the lead ion with large ionic radii. The AC-conductivity was increased from (1.523 × 10^?5 to 6.699 × 10^?5) Ωcm^?1. The dielectric constant and tangent loss was found to decrease substantially. The magnetic properties were found to enhance by the substitution of Yb³⁺. The low coercivity value of Yb³⁺ substituted W-type hexagonal ferrites are suitable for magnetic recording media operated at a high-frequency regime. The enhancement of electrical, dielectric and magnetic characteristics suggests these materials as promising for multi-layer chip inductors (MLCIs) circuit applications.     

Effect of organic solvent on the cold sintering processing of SrFe12O19 platelet-based permanent magnets

In this work we have investigated the effect of the solvent during the processing of SrFe₁₂O₁₉ platelet-based permanent magnets by cold sintering process (CSP) plus a post-thermal treatment. Several organic solvents: glacial acetic acid, oleic acid and oleylamine have been analyzed, optimizing the CSP temperatures at 190?270 °C, under pressures of 375?670 MPa and 6?50 wt% of solvent. Modifications in the morphological and structural properties are identified depending on the solvent, which impacts on the magnetic response. Independently of the solvent, the mechanical integrity of ferrite magnets obtained by CSP is improved by a post-annealing at 1100 °C for 2 h, resulting in relative densities around 92 % with an average grain size of 1 μm and a fraction of SrFe₁₂O₁₉ phase >91 %. H_C ≥ 2.1 kOe and M_S of 73 emu/g are obtained in the final sintered ceramic magnets, exhibiting the highest H_C value of 2.8 kOe for the magnet sintered using glacial acetic acid.     

Magnetic properties,phase evolution,hollow structure and biomedical application of hematite (α-Fe2O3) and QUAIPH

We investigate synthesis, phase evolution, hollow and porous structure and magnetic properties of quasi-amorphous intermediate phase (QUAIPH) and hematite (α-Fe₂O₃) nanostructure synthesized by annealing of akaganeite (β-FeOOH) nanorods. It is found that the annealing temperature determines the phase composition of the products, the crystal structure/size dictates the magnetic properties whereas the final nanorod morphology is determined by the starting material. Annealing of β-FeOOH at ～300 °C resulted in the formation of hollow QUAIPH nanorods. The synthesized material shows low-cytotoxicity, superparamagnetism and good transverse relaxivity, which is rarely reported for QUAIPH. The QUAIPH nanorods started to transform to porous hematite nanostructures at ～350 °C and phase transformation was completed at 600 °C. During the annealing, the crystal structure changed from monoclinic (akaganeite) to quasi-amorphous and rhombohedral (hematite). Unusually, the crystallite size first decreased (akaganeite → QUAIPH) and then increased (QUAIPH → hematite) during annealing whereas the nanorods retained particle shape. The magnetic properties of the samples changed from antiferromagnetic (akaganeite) to superparamagnetic with blocking temperature T_B = 84 K (QUAIPH) and finally to weak-ferromagnetic with the Morin transition at T_M = 244 K and high coercivity H_C = 1652 Oe (hematite). The low-cytotoxicity and MRI relaxivity (r₂ = 5.80 mM^?1 s^?1 (akaganeite), r₂ = 4.31 mM^?1 s^?1 (QUAIPH) and r₂ = 5.17 mM^?1 s^?1 (hematite)) reveal potential for biomedical applications.     

Anchor plate bearing capacity in flexible mesh facings

This work addresses the problem of the loading capacity of an anchor plate coupled with a steel wire mesh in soil retaining applications. The interaction mechanism between the flexible mesh facing, the underlying soil layer and the plate is studied starting from the results of several laboratory punch tests involving both the plate and the mesh only, and the whole soil-mesh-plate system. The experimental tests have been reproduced by adopting a 3D discrete element model where also the wire mesh is discretized as an assembly of interconnected nodal particles. The interaction between these particles is ruled by elasto-plastic tensile force–displacement laws in which a distortion is introduced in a stochastic manner to account for the wires’ geometrical irregularities. The mesh model is then validated with reference to a set of punch tests in which the shape and size of the punching element as well as the nominal wire diameter were varied. Subsequently, the model is extended to a punch against soil test configuration permitting an insight into the nontrivial local mechanism between the mesh facing and the underlying granular layer. The good agreement between the numerical predictions and the experimental observations at the laboratory scale allowed us to extend the model towards more realistic field conditions for which the role of the mesh panel boundary conditions, the mesh mechanical properties, the soil mechanical properties and the anchor plate geometry is investigated.     

Effect of Pr-Ga dual-alloys diffusion on magnetic properties and thermal stability of hot-deformed PrNd-Fe-B magnets

To investigate the influence of the addition of Pr–Ga alloys on magnetic properties and morphology of materials, the hot-deformed PrNd-Fe-B magnets were prepared by the addition of Pr–Ga alloys using a dual-alloys diffusion. The room-temperature coercivity of the hot-deformed PrNd-Fe-B magnets increases substantially from 1.68 to 2.34 T, while the remanence decreases from 1.42 to 1.24 T, by the addition of 5 wt% Pr–Ga alloys. Moreover, the thermal stability of coercivity improves from ?0.46%/^oC to ?0.42%/^oC. Two types of grain boundary phases (PrNd-rich and PrNd-Ga-rich) are generated at grain boundaries by microstructural analysis, resulting in the decrease of Fe element concentration from more than 60% to about 10% at grain boundaries. The decrease of ferromagnetic element concentration at grain boundaries and the refinement of grain are considered to be the main reasons for the improvement of coercivity and thermal stability.     

Observation of table-like magnetocaloric effect and large refrigerant capacity in Nd6Fe13Pd1–xCux compounds

The table-like magnetocaloric effect is significant for the magnetic refrigeration applications above 20 K based on the Ericsson cycle. Herein, we prepared a series of Nd₆Fe₁₃Pd_1–xCu_x (x = 0.05, 0.1, 0.15) compounds by the arc-melting method. These compounds show the single crystalline phase in the tetragonal Nd₆Fe₁₃Si-type structure with the space group I4/mcm. A magnetic phase transition from ferromagnetism to antiferromagnetism and a metamagnetic transition from the antiferromagnetic state to the ferromagnetic state are observed in each of the compounds. The compounds exhibit table-like magnetocaloric effects with large refrigerant capacities. A constant ΔS_M in a temperature span of 40 K in the Nd₆Fe₁₃Pd_0.85Cu_0.15 compound are observed. For a field change of 0–5 T, the peak values of –ΔS_M for the Nd₆Fe₁₃Pd_0.95Cu_0.05, Nd₆Fe₁₃Pd_0.90Cu_0.10, and Nd₆Fe₁₃Pd_0.85Cu_0.15 compounds are estimated to be 4.8, 4.6 and 4.4 J/(kg·K) with corresponding refrigerant capacity values of 323, 331 and 316 J/kg, respectively. The obtained table-like magnetocaloric effects with large refrigerant capacities as well as fairly small thermal and magnetic hysteresis deem these series of compounds good candidates for single-phase magnetic refrigeration based on the Ericsson cycle.     

A comparative study of NdY-Fe-B magnet and NdCe-Fe-B magnet

Low cost and high abundance rare earth elements Y and Ce have attracted tremendous interests of the industrial and scientific societies for fabricating the highly cost-performance efficient rare earth permanent magnets. However, the effect of separate replacement of Nd by Y or Ce on the performances of NdFeB-type magnet under the same atomic ratio and preparation conditions is still unclear. In this work, we systematically investigated the magnetic properties, thermal stabilities and service performances of (Nd_0.8Y_0.2)_13.80Fe_balAl_0.24Cu_0.1B_6.04 (atomic fraction, denoted as 20Y) and (Nd_0.8Ce_0.2)_13.80Fe_balAl_0.24Cu_0.1B_6.04 (atomic fraction, denoted as 20Ce) magnets. The results demonstrate that the μ₀M_r, μ₀H_c and (BH)_max of 20Y magnet are respectively 1.325 T, 1.173 T and 343.467 kJ/m³, which are comprehensively higher than those of 20Ce magnet (μ₀M_r = 1.310 T, μ₀H_c = 0.948 T, (BH)_max = 321.105 kJ/m³). Moreover, the 20Y magnet has higher thermal stability compared with 20Ce magnet which is favorable for the magnetic performances at elevated temperatures. The investigation of microstructure and elemental distribution indicates that the excellent magnetic performances of NdY-Fe-B magnet can be attributed not only to the preferable intrinsic properties 4πM_s, H_a and T_c of Y₂Fe₁₄B, but also to the in-situ core–shell structure of the 2:14:1 matrix phase grain with Y-rich core and Nd-rich shell, along with the thicker grain boundary layer between the adjacent matrix phase grains in NdY-Fe-B magnet. Furthermore, the 20Y magnet exhibits better mechanical property and higher corrosion resistance than 20Ce magnet, which are helpful for prolonging the service life of the magnet in practical application.     

The structure,vacancy characteristics,and magnetic properties of GdMn1-xCrxO3 ceramics

To investigate the evolution of the structural and enhanced magnetic properties of GdMnO₃ systems induced by the substitution of Mn with Cr, polycrystalline GdMn_1-xCr_xO₃ samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn_1-xCr_xO₃ compounds with single-phase structures crystallize well and that Cr³⁺ ions entering the lattice sites of GdMnO₃ induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn_1-xCr_xO₃ ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn_1-xCr_xO₃. The enhanced magnetization of GdMn_1-xCr_xO₃ is closely related to the vacancy defect concentration.