Amorphous high-entropy alloys (HEAs) as electromagnetic-wave absorbing materials have been rarely reported. In this work, amorphous FeCoNiTixSi HEAs were synthesized by introducing a high content of ...large-atom Ti using the high-energy ball-milling technique. This amorphous structure could improve the saturated magnetization and coercivity of HEAs, but slightly degraded the mechanical and oxidation resistance properties. In terms of electromagnetic properties, FeCoNiTi0.01Si and FeCoNiTiSi exhibit excellent electromagnetic-wave absorption performances, with significant absorptions of −68.4 dB at 6.14 GHz and −63.4 dB at 9.12 GHz, corresponding to bandwidths of 5.15 GHz (1.69 mm) and 3.64 GHz (1.43 mm), respectively. Overall, the prepared FeCoNiTixSi HEAs exhibited superior comprehensive performances compared to other HEA absorption materials. This work provided a novel strategy for the development of new electromagnetic-wave absorption materials with low weight, high absorption efficiency, and resistance to harsh environments.
•The exchange coupling could not be neglected in improving the coercivity in the sintered magnets.•The increase of activation volume implies that the exchange coupling is effective in magnetization ...reversal.•Both a high coercivity of 20.0 kOe and a high energy product of 50.1 MGOe are achieved in the composite magnets.
Preparing the magnetic materials bearing both a high coercive field and a high energy product is a great challenge. In this paper the content of Nd was reduced in Nd-Fe-B for enhancing the interaction effect as well as for increasing the energy product, and Tb-Fe-B powders were mixed to enhance the coercivity. In the sintered RE-Fe-B magnets some of Tb atoms diffuse into the outer regions of Nd-Fe-B grains, and Tb-rich RE2Fe14B grains also exist with the crystal size at micrometer scale. The recoil loops bear the spring behaviors, and the reversal susceptibility implies the availability of exchange coupling effect among the micro grains. The activation volume also indicates that the exchange coupling is effective in magnetization reversal. So the magnetization reversal in Nd-Fe-B grains could be restrained by the high anisotropy phase of Tb-rich core. Therefore, besides the effects of Tb-diffusion into grain outer region and the intergranular phase, the exchange coupling effect could not be neglected in improving the coercivity in the Nd-content-reduced magnets, and both a high coercive field of 20.0 kOe and a high energy product of 50.1 MGOe are achieved in the micro-crystal composite magnets.
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•The nanoferrites are considered based on their atomic number.•The dependency of magnetic property on the different properties were discussed.•Smaller crystallite size nanoparticles ...shows larger coercivity.•Correlation between crystallinity and magnetic behavior were discussed.
Nano ferrites with molecular formula AFe2O4 (A = Mg, Mn, Co, Ni, Cu, Zn and Ba) are considered as better magnetic materials than pure metals. Iron NPs present in the nano ferrite possess high magnetic moment which gives better magnetic signals and improves the sensitivity. The high resistance, saturation of magnetization, permeability, coercivity, low cost and less power loss property of nano ferrites made them find applications in different fields. The magnetic property arises due to the interaction between metal ions occupying a particular position and oxygen ions. The occupancy of metal ions depends on the method of synthesis. The coercivity, saturation magnetization and retentivity of certain ferrites such as Magnesium ferrite, Manganese ferrite, Nickel ferrite, copper ferrite and barium ferrite were found to be maximum for autoclave, chemical bath deposition, sol gel, sol gel auto combustion methods whereas found to be minimum for coprecipitation, thermal heat treatment, auto combustion and mechanical alloying method. The change in the method of synthesis, synthesis atmosphere, calcination/annealing temperature leads to the development of oxygen content which is going to affect directly/indirectly the magnetic properties. In this brief review, we have studied the dependency of magnetic ferrites such as saturation of magnetization, retentivity and coercivity on the crystallite size and calcination temperature synthesized via different methods. We have discussed more than 70 experiments reported by different researchers.
Rhodamine B (RhB), as perilous contaminants vastly utilized in industrial purposes, has potential role in environmental pollution. In present study a series of nanocrystalline rare earth (Sm3+) ...substituted magnesium-zinc ferrite with composition Mg0.2Zn0.8SmxFe2-xO4; (0 ≤ x ≤ 0.2) (MZS), for RhB degradation, were scrutinized. The sharpness and prevalence of XRD peaks emphasize its nanocrystalline nature. The lattice constant (aexp) is found to increase from 8.3818 to 8.4215 Å; obeying Vegard’s law, with (311) peak shift from 2θ = 35.28ο to 34.32°. Bond dissociation energy of (Sm–O) is the reason for why the crystallite size (DWH) of MZS nanoferrites was increased by Sm/Fe substitution process; declaring an inverse relation between DWH and aexp values. Triple factors; magnetic moment of Sm/Fe cations in octahedral sites, crystallite size and porosity are responsible for the decrement behavior of saturation magnetization. The coercivity has a unique attitude; firstly exhibits a downward behavior and then an upward one. The dielectric parameters have unique behavior with Sm3+ substitution; firstly decrease (0.0 ≤ x ≤ 0.12) and then increases (0.12 ≤ x ≤ 0.2); governed by substitution ions, porosity and crystallite size effects. Nyquist plots have a distinct arc; meanwhile the second one is wholly unseen, due to one of two prospects. The optical energy gap has a special behavior; it has a blue shift from (1.74eV–2.06eV; for 0.0 ≤ x ≤ 0.12), and then a red shift from (2.06 eV–1.61 eV; for 0.12 ≤ x ≤ 0.2) by two justifications. The photo-decolorization efficiency of RhB over MZS photocatalysts is enhanced; (10.76%, 22.05%, 38.08%, 58.93%, 77.10% and 94.13% with increasing Sm3+ content, respectively) compared with its modest value 4.91% without addition. All these outcomes could provide insight into electronic devices besides photocatalyst for RhB removal by Mg0.2Zn0.8Sm0.2Fe1.8O4 ferrite nanoparticles.
•MZS nanoparticles have been synthesized by a combustion method.•Bond dissociation energy of (Sm–O) is the reason for the crystallite size behavior of MZS nanoferrites.•Triple factors; magnetic moment values, crystallite size and porosity are responsible for MS decrement.•Nyquist plots have a distinct arc; meanwhile the second one is wholly unseen, due to one of two prospects.•The photodegradation efficiency of RhB over MZS photocatalysts is enhanced.
In this study, manganese substituted strontium hexaferrite (SrFe12−xMnxO19; x = 0, 3, 5, and 7) prepared by the sol–gel auto-combustion method are studied. We observed that the substituted Mn ...preferentially goes to the 2a and 12k sites of Fe. Raman modes related to the 12k site suggest the stiffening of the lattice. The transformation of the grain's shape from hexagonal (x = 0 and 3) to rhombohedral (x = 7) was observed, as shown in the micrographs obtained from FESEM. The thermomagnetic curves show the shift of TC to lower temperatures with the increase in the Mn content. From x = 5 onwards, the growth of another magnetic phase (FiM2) of lower coercivity apart from the parent phase (FiM1) of higher coercivity is seen. The FiM2 phase was found to increase with the Mn content in the sample (16.4(3)% for x = 5 but 66.2(5)% for x = 7). Although the magnetization for both FiM1 and FiM2 decreases with the increase in temperature, both magnetic phases behave in contrast to each other for x = 5 and x = 7. The study suggests a transformation of the compound from high magnetic anisotropy (x = 0) to low magnetic anisotropy (x = 7). The x = 5 composition sample displays the highest value of the first-order ME coefficient (0.83(2) mV × cm−1 × Oe−1). The observed value for x = 5 composition is ∼2.5 times higher than that of the parent x = 0 composition sample (0.33(2) mV × cm−1 × Oe−1). The studies thus suggest that the x = 5 composition is one of the viable candidates for magnetoelectric applications.
The wide range of wildlife tracking and surveillance technologies (radio and satellite tracking, cameras, and audio) that are being deployed in conservation have important implications for a ...geographical understanding of care for non-human nature. This report explores four dimensions of their influence. First, their detailed view of spatial dimensions of non-human lives affects conservation’s demarcation and control of space. Second, the application of surveillance technologies to people is central to the rise of coercive conservation strategies. Third, such technologies enable the creation and commoditization of spectacular nature. Fourth, spatial digital data enables the automation of conservation decisions, a trend described here as ‘conservation by algorithm’.
Transmission eigenvalues play an important role in the inverse scattering theory. In this paper, we study the mixed discontinuous Galerkin method for the transmission eigenvalue problem and the ...modified transmission eigenvalue problem for anisotropic inhomogeneous medium in
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. We use the
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•High pressure hydrogen milling was successfully used to produce Nd2Fe14B-based magnets with tunable grain size.•Coercivity peaks around the analytically calculated single domain grain size of ...≈200 nm for Nd2Fe14B.•Higher contents of Nd-rich grain boundary phase lead to a continuous increase in coercivity up to μ0Hc = 1.5 T.
Nd2Fe14B-based permanent magnets play important role in the emerging green energy technologies due to their superb energy product (BH)max. High coercivity at elevated operating temperatures is crucial for device performance and as an extrinsic property it is largely determined by the microstructure of the magnet. In this work, we use high pressure hydrogen milling to reduce the average grain size in Nd2Fe14B powders towards the critical single domain regime to study the influence on the resultant coercivity. In addition, Nd content has been varied in a broad range to investigate how it affects the coercivity. Milling in 100 bar hydrogen enables complete decomposition of the Nd2Fe14B phase into α-Fe, NdH2 and Fe2B at nominally room temperature. A subsequent hydrogen desorption heat treatment leads to the recombination to the parent phase, now with nearly two orders of magnitude reduction in the grain size. The results show that indeed Hc peaks around the critical single domain grain size of ≈200 nm of Nd2Fe14B. Higher contents of Nd-rich grain boundary phase lead to a continuous increase in coercivity up to μ0Hc = 1.5 T, likely due to the suppression of long-range magnetostatic interactions between the nanocrystalline Nd2Fe14B grains.
•Nd28.5Fe66.5Dy4B1 (wt.%) ribbons was prepared at different wheel speeds in the range of 15 to 30 m/s.•Columnar grains was formed near air surface of ribbons at wheel speeds above 20 m/s.•The ...columnar grains are induced due to heat extraction and the movement of the Nd-rich phase.•Compared to isotropic grains, the magnetic properties of SPS magnets are enhanced by the existence of short columnar grains.
In this work, we investigated the formation of columnar grain microstructure of melt - spun Nd28.5Fe66.5Dy4B1 (wt.%) (Nd-Fe-B) alloy and concurrently, studied their effect on the magnetic properties of the spark plasma sintered (SPS) Nd-Fe-B bulk. The melt spinning was performed at different wheel speeds in the range of 15 to 30 m/s. The formation of columnar grains perpendicular to the plane of the ribbons were examined through SEM and the XRD result reveals the strong (00 l) crystal texture. The mechanism behind the formation of columnar grains in melt-spun ribbon and the magnetic properties of the sintered Nd-Fe-B bulks were deeply discussed. The obtained Nd-Fe-B magnet realizes enhanced magnetic properties through the controlled microstructure of melt-spun ribbons including columnar grain regions along with equiaxed grain regions. Eventually, it shows an improved coercivity of 17.3 kOe and remanence at 7.2 kG, which is 22% and 6%, respectively, larger than the magnet containing isotropic grains alone.
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