The annealing temperature dependent on the structural and magnetic properties of hematite (α-Fe2O3) powders synthesized via the sol-gel method was studied. The sol-gel method is used to prepare ...nanoparticles for this experiment. The annealing treatment of 200°C, 400°C, 600°C, and 800°C has been carried out to modify the physical properties. The obtained nanoparticles are characterized by their structural properties using X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Then, magnetic properties were evaluated using Vibrating Sample Magnetometer (VSM). XRD results have shown an increase in crystallite size with an increase in annealing temperature from 35.10 nm to 60.17 nm. The increase in crystallite size can be attributed to the increase in the crystal structure’s internal energy, which promotes atomic diffusion. The FTIR results show an absorption that appears at the peak around ~530 cm-1. It indicates that the Fe3+ cation has successfully formed. The VSM results show an increase in the value of Hc with an increase in the annealing temperature from 117 Oe to 461.5 Oe. It is supported by the increase of anisotropy constant and increasing temperature annealing.
•The Sn added MnBi bulk magnets were prepared by hot compaction process, and it was found that it has superior coercivity compared to pure MnBi bulk magnets.•The coercivity (Hc) of Sn added MnBi bulk ...magnets could be effectively enhanced due to the construction of intergranular phases.•The (BH)max of 1 wt.% Sn added MnBi bulk magnet is recorded of 7.84 MGO, which shows a 7% increase compared to the pure MnBi bulk magnet.•The Sn added MnBi bulk magnet with enhanced coercivity, making it a promising candidate for the next-generation rare-earth-free permanent bulk magnets.
The Sn addition MnBi bulk magnets with high density and superior coercivity (Hc) were prepared by hot compaction. It was found that the added Sn was dispersed between the MnBi particles as an intergranular phase. The appropriate intergranular phase content could be beneficial in improving the Hc due to the strong magnetic isolation effects. The Hc of the MnBi/Sn bulk magnet was increased from 8.6 kOe to 11.5 kOe as the Sn addition contents were increased in the range of 0 wt.% to 5 wt.%. A relatively high squareness (Mr/Ms) of 0.91 was obtained for the 1 wt.% Sn addition Mn56Bi44 bulk magnet exhibiting the maximum energy product (BH)max of 7.8 MGOe with high Hc of 10 kOe at room temperature.
Abstract
Pollution is one of the big problems of continuous pollution in the Brantas River. The type of pollution that occurs in the sediment of a river is associated with the characteristics of its ...magnetic mineral. This study aims to determine the types of magnetic minerals in the Brantas River sediments. IRM data was taken from the measurement results in the Brantas River sediments. In this study, the IRMITS program is used to provides a deeper and better analysis and interpretation. From the processing results, IRMITS produces 3 graphs, namely the Linear Acquisition Plot (LAP) curve (b) the Gradient Acquisition Plot (GAP) curve; (c) Standardized Acquisition Plot (SAP) curve. From this study that has been done, it shows that magnetic minerals in the Brantas River are saturated in magnetic fields above 800mT with permanent coercivity occurring in the range 12-13 x 10
−3
and z value 0 before saturation occurs. This indicates that most of the Brantas River sediments is dominated by magnetite minerals (Fe
3
O
4
).
A large coercive field (E
) and ultrahigh piezoelectricity are essential for ferroelectrics used in high-drive electromechanical applications. The discovery of relaxor-PbTiO
crystals is a recent ...breakthrough; they currently afford the highest piezoelectricity, but usually with a low E
. Such performance deterioration occurs because high piezoelectricity is interlinked with an easy polarization rotation, subsequently favoring a dipole switch under small fields. Therefore, the search for ferroelectrics with both a large E
and ultrahigh piezoelectricity has become an imminent challenge. Herein, ternary Pb(Sc
Nb
)O
-Pb(Mg
Nb
)O
-PbTiO
crystals are reported, wherein the dispersed local heterogeneity comprises abundant tetragonal phases, affording a E
of 8.2 kV/cm (greater than that of Pb(Mg
Nb
)O
-PbTiO
by a factor of three) and ultrahigh piezoelectricity (d
= 2630 pC/N; d
= 490 pC/N). The observed E
enhancement is the largest reported for ultrahigh-piezoelectric materials, providing a simple, practical, and universal route for improving functionalities in ferroelectrics with an atomic-level understanding.
Engineering intramolecular exchange interactions between magnetic metal atoms is a ubiquitous strategy for designing molecular magnets. For lanthanides, the localized nature of 4f electrons usually ...results in weak exchange coupling. Mediating magnetic interactions between lanthanide ions via radical bridges is a fruitful strategy towards stronger coupling. In this work we explore the limiting case when the role of a radical bridge is played by a single unpaired electron. We synthesize an array of air-stable Ln
@C
(CH
Ph) dimetallofullerenes (Ln
= Y
, Gd
, Tb
, Dy
, Ho
, Er
, TbY, TbGd) featuring a covalent lanthanide-lanthanide bond. The lanthanide spins are glued together by very strong exchange interactions between 4f moments and a single electron residing on the metal-metal bonding orbital. Tb
@C
(CH
Ph) shows a gigantic coercivity of 8.2 Tesla at 5 K and a high 100-s blocking temperature of magnetization of 25.2 K. The Ln-Ln bonding orbital in Ln
@C
(CH
Ph) is redox active, enabling electrochemical tuning of the magnetism.
•CoxFe3−xO4 NPs are synthesized by a thermal decomposition continuous growth approach.•The size and composition of the NPs are controlled by the reaction conditions.•Freezing the NPs in an oriented ...condition leads to a remanence and coercivity enhancement.•The enhancement of the magnetic properties depends on the structure of the NPs.•At the oriented condition, the “hardest” NPs reaches coercive fields of ≈ 30 kOe at 5 K.
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The macroscopic magnetic behavior of nanoparticulated systems is the result of several contributions, ranging from the intrinsic structural properties of the nanoparticles to their spatial arrangement within the material. Unravelling and understanding these influences is an important task to produce nano-systems with improved properties for specific technological applications. In this work we study how the magnetic behavior of a set of magnetically hard nanoparticles can be improved by the modification of the sample arrangement (either randomly or magnetically oriented) and the nature of the enclosing matrices. At first, we employed a hot-injection, continuous growth strategy to synthesize non-stoichiometric cobalt ferrite (CoxFe3−xO4) nanoparticles. We prepared five batches of hydrophobic, oleate-coated samples, with mean diameters of 8 nm, 12 nm, 16 nm and variable Co-to-Fe proportions. The structural characterization confirms that the nanoparticles have a spinel-type monocrystalline structure and that the Co and Fe ions are homogenously distributed within the system. The magnetic properties of the nanoparticles were measured by DC magnetometry, and we found that the strategy used in this work to create a system of magnetically oriented nanoparticles can lead to a significant remanence and coercive field enhancement at low temperatures when compared with randomly oriented and fixed systems. The modification of the magnetic properties was detected in the five batches of samples, but the strength of the enhancement depends on both size and composition of the nanoparticles. Indeed, for the “hardest” samples the coercive field of the magnetically oriented systems reached values of around 30 kOe (3 T), which represents a 50% increase regarding the randomly oriented system and are among the highest reported to date for a set of Fe and Co oxide nanoparticles.
A new kind of multifunctional L10‐Mn1.5Ga film is demonstrated for the first time. These MBE‐grown epitaxial films exhibit pronounced magnetic properties at room temperature, including ultrahigh ...perpendicular coercivity up to 42.8 kOe, giant perpendicular magnetic anisotropy with a maximum of 21.7 Merg/cm3 and large magnetic energy products up to 2.60 MGOe, which allow various applications in ultrahigh density recording, spintronics, and permanent magnets.
We introduce a novel method to develop high coercivity with improved squareness in bulk hot-deformed Nd–Fe–B magnets with a thickness of 5.6 mm. A low-melting-point Tb20Dy10Nd40Cu30 eutectic ...diffusion source was infiltrated into the thick magnets through grain boundaries as the 1st step, followed by the 2nd step eutectic diffusion using Nd80Cu20. The 1st step led to the formation of rare earth (RE)-rich intergranular phase as well as heavy rare earth (HRE)-rich shell surrounding platelet-shaped Nd2Fe14B grains. A large concentration gradient toward the center of the thick magnet caused a large switching field distribution, which was the main limitation of this method after the first step and in the conventional infiltration process. The second step Nd-Cu diffusion makes the HRE-shell more uniform throughout the entire volume, which improved the squareness factor from 0.83 to 0.91 with a slight coercivity increase from 2.38 T to 2.43 T. Magneto-optical Kerr effect microscopy showed unlike the conventional infiltration processed magnet, strong pinning of the magnetic domain wall motion at the side grain boundaries occur even in the near center of the two step diffusion processed magnet.
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Room temperature magnetic properties and coercivity mechanisms for nanocomposites (La0.5Ce0.5)1−xREx10Fe84B6 (RE=Nd or Dy; x=0, 0.3, 0.5, and 0.7) alloys prepared by melt-spinning have been ...investigated. Nd and Dy substitutions can improve the hard magnetic properties, especially the coercivity of (La0.5Ce0.5)10Fe84B6 alloy. The largest values of intrinsic coercivity Hc and maximum energy product (BH)max for the Dy substituted alloys are 714kA/m and 41kJ/m3, respectively, whereas for Nd substituted alloys, Hc=365kA/m and (BH)max=120kJ/m3 were obtained for x=0.7. The different elevated temperature behaviors were also found for Nd and Dy added alloys. The composition dependent coercivity mechanisms for Dy and Nd substituted alloys are evident based on the temperature dependence of coercivity described by domain wall pinning and reverse domain nucleation models. It is found that the domain wall pinning mechanism is possibly responsible for (LaCe)NdFeB alloys while reverse domain nucleation is more likely responsible for(LaCe)DyFeB alloys.
•Properties and coercivity mechanism were discussed for (LaCe)FeB nanocomposites.•Dy substituting LaCe increased the coercivity but reduced the remanence.•Nd substitution enhanced the coercivity, remanence and energy product.•Dominant coercivity mechanism observed in Dy substituted sample is nucleation.•Pinning mechanism was observed in Nd substituted sample.
The barium ferrite BaFe12O19 with c-plane anisotropy, which possessed relative high saturation magnetization and low coercivity, had been synthesized by hydrothermal method with different reaction ...time of 5 h, 8 h,11 h,14 h, and 17 h. The X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM) were used to study the phase composition, microstructure and magnetic properties of barium ferrite, respectively. The results showed the intensities of the peak were enhanced and there was no impurity phase. With the prolonging of the reaction time to 11 h, 14 h and 17 h, the grain size increased, and the equivalent diameter was about 1 μm, and the thickness was about 100 nm. When the reaction time was 17 h，the coercivity of barium ferrite was 1104 Oe. The reduction of coercivity was ascribed to the increase of particle size and the reduction in magnetic anisotropy.
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