Characterization and Applications of Metal Ferrite Nanocomposites

In recent years, nanosized spinel-type ferrites emerged as an important class of nanomaterials due to their high electrical resistivity, low eddy current loss, structural stability, large permeability at high frequency, high coercivity, high cubic magnetocrystalline anisotropy, good mechanical hardness, and chemical stability [...]

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)z Permanent Magnets: III. Matrix and Phases of the High-Coercivity State

Observations of the surface domain structure (Kerr-effect), optical metallography, scanning electron microscopy (SEM-SE), and electron microprobe analysis (EPMA-SEM), measurements of major and minor magnetic hysteretic loops were used to study pseudo-single-crystal samples of (Sm,Zr)(Co,Cu,Fe)z alloys subjected to heat treatments to the high-coercivity state, which are used in fabricating sintered permanent magnets. Correlations between the chemical composition, hysteretic properties, structural components, domain structure, and phase state were determined for the concentration ranges that ensure wide variations of 4f-/4d-/3d-element ratio in the studied samples. The phase state formed by collinear and coherent phase components determines the high coercive force and ultimate magnetic hysteresis loops of the pseudo-single crystals. It was found that the 1:5 phase with the hexagonal structure (P6/mmm) is the matrix of the alloys for (Sm,Zr)(Co,Cu,Fe)z permanent magnets; the matrix undergoes phase transformations in the course of all heat treatments for the high-coercivity state. The heterogeneity observed with optical magnifications, namely, the observation of main structural components A and B, is due to the alternation, within the common matrix, of regions with modulated quasi-spherical precipitates and regions with hexagonal bipyramids (cellular phase) although, traditionally, many investigators consider the cellular phase as the matrix. It is shown that the relationship of volume fractions of structural components A and B that account for more than 0.9 volume fraction of the total, which is due to the integral chemical composition of the alloys, determines the main hysteretic performances of the samples. The Zr-rich phases, such as 5:19, 2:7, and 6:23, and a structural component with the variable stoichiometry (Sm(Co,Cu,Fe)3.5–5) that is almost free of Zr and contains up to 33 at% Cu, were found only within structural component A in quantities sufficient for EPMA analysis.

The High Coercivity Field in Chemically Bonded WSe2/MoSe2 Powder

We studied the magnetic properties of WSe2/MoSe2 powder. The coercivity field reaches 2600 Oe at 5 K, 4233 Oe at 100 K and 1300 Oe at 300 K. These are the highest values reported for two-dimensional transition metal dichalcogenides. This study is different from the widely reported vacancy and zigzag structure-induced ferromagnetism studies. Importantly, a Raman peak red shift was observed, and that supports the chemical bonding at the interface between WSe2 and MoSe2. The large coercivity field originates from the chemical bonding-induced structural distortion at the interface between WSe2 and MoSe2.

Optical and magnetic properties of orthoferrite NdFeO3 nanomaterials synthesized by simple co-precipitation method

In this work, orthoferrite NdFeO3 nanomaterials with particle sizes 20-40 nm have been successfully synthesized via a simple co-precipitation method through the hydrolysis of Nd (III) and Fe (III) cations in hot water with 5% NaOH as a precipitating agent. Single-phase NdFeO3 was generated after calcination of the as-prepared powder at 700, 800, and 900 °C for 1 hour. The UV-Vis spectra at room temperature presented strong absorption in the UV-Vis regions (l = 200–400 nm and 400–600 nm) with small band gap energy (Eg = 2.2÷2.5 eV). The obtained NdFeO3 nanomaterials exhibited a hard ferromagnetic behavior with high coercivity (Hc = 600–1600 Oe).

A Sediment Magnetic Record in the North Pacific Across the Mid-Pleistocene Transition and its Implication on Asian Dust Evolution

Eolian dust deposited in the North Pacific is an important archive of the evolutionary history of Asian interior source regions and climate system. Here, we present a ∼1 Myr sediment magnetic record from the central North Pacific to characterize eolian dust properties since the middle Pleistocene. For the studied sediments, magnetic components are mainly identified as biogenic magnetite and detrital magnetic minerals (dust and volcanic origins) based on coercivity analysis, microscopic observations, and sedimentological information. The detrital magnetic component is characterized by high coercivity (>100 mT) and shows a long-term increase in concentration since ∼1 Ma. In particular, the concentration shows a considerable increase at ∼0.8–0.7 Ma compared to the inorganic silicate fraction, indicative of magnetic mineral enrichment in detrital sediment fraction. At the same time, the coercivity distribution of the detrital component also decreases, which can be attributed to an increase in the ferrimagnetic mineral contribution. As the detrital sediments are primarily wind-blown particles, such ferrimagnetic enrichment implies a change in dust source materials after ∼0.8 Ma, which could be explained by the reorganization of atmospheric circulation and/or regional aridification in source regions across the mid-Pleistocene transition. The dust property change in source areas is likely to be synchronized across the North Pacific based on the similarity of the long-term trend of magnetic signals.

Formability and Magnetic Properties of the Binary Nd-Co Amorphous Alloys

In this paper, binary Nd-Co alloys with compositional range from Nd72.5Co27.5 to Nd50Co50 were successfully vitrified into glassy state by a melt-spinning method. The glass formability of the metallic glasses (MGs) was studied and the best glass former in the binary Nd-Co alloys was obtained. Magnetic properties of the MGs were measured. The compositional dependence of Curie temperature of the MGs was observed. The mechanism for the spin-glass-like behaviors and high coercivity at low temperature, and their influence on the magnetic entropy change of the MGs, were investigated.

Rock Magnetism of Late Cretaceous to Middle Eocene Strata in the Lesser Himalaya, Western Nepal: Inferences Regarding the Paleoenvironment

The growth of the southern piedmont of the Himalayan boundary and its depositional setting has changed since uplift of the Himalaya due to continental Indian-Eurasian collision, which has resulted in variation in magnetic minerals in marine- and terrestrial-facies sediments. In this paper, we utilize rock magnetism data from the late Cretaceous to middle Eocene strata, including the Amile and Bhainskati formations from the Lesser Himalaya (western Nepal), to understand the mechanism controlling magnetic susceptibility (χ). The active tectonics strongly influenced saturation isothermal remanent magnetization (SIRM), HIRM, and hysteresis loops, forming both low-coercivity minerals in sediments with low χ from the terrestrial facies (zones I, IIIA, and V) and high-coercivity minerals in the sediments with high χ from the marine facies (zones II, IIIB and IV). Thermomagnetic κ-T curves and frequency-dependent χ (χfd%) values show that sediments with low χ and high χ carry magnetite with coarse non-superparamagnetic (SP) grains and hematite with SP grains, respectively. Comparing the χ data with the lithologic, sedimentary environments, geomorphic features, and sea level data, we propose that low χ values were mainly produced by an increase in terrigenous detrital influx during the regression period of the Tethys Sea, while high χ values formed in marine sediments, which prompted the appearance of ferromagnetic-antiferromagnetic and paramagnetic minerals during the transgression of the Tethys Sea.

Effect of Drying Temperature on the Magnetic and Microstructural Properties of BaFe12O19 Synthesized by Coprecipitation Method

Barium hexaferrite (BaFe12O19) has dominated many aspects of technology, serving as a permanent magnet, magnetoelectric, multiferroic, and electric motors, generators, microwave devices, and drug delivery systems. There is a challenge in the synthesis of BaFe12O19 with the coprecipitation method. As a result, research is conducted to examine the factors influencing the properties of BaFe12O19 during the preparation process, specifically on the drying temperature of the mixture. The precursors were precipitated, through some procedural steps, along with stirring at 450 rpm at a certain temperature for a while and simultaneously pouring the precipitant dropwise; the sample was dried at different temperatures. The final samples were annealed at the same rate of temperature within the same time interval. The results depicted that drying at different temperatures leads to the variation in the magnetic and microstructural properties of BaFe12O19, indicating that drying at high temperatures resulted in high coercivity with low saturated magnetization.

Recent Advances in Synthesis and Applications of MFe2O4 (M = Co, Cu, Mn, Ni, Zn) Nanoparticles

In the last decade, research on the synthesis and characterization of nanosized ferrites has highly increased and a wide range of new applications for these materials have been identified. The ability to tailor the structure, chemical, optical, magnetic, and electrical properties of ferrites by selecting the synthesis parameters further enhanced their widespread use. The paper reviews the synthesis methods and applications of MFe2O4 (M = Co, Cu, Mn, Ni, Zn) nanoparticles, with emphasis on the advantages and disadvantages of each synthesis route and main applications. Along with the conventional methods like sol-gel, thermal decomposition, combustion, co-precipitation, hydrothermal, and solid-state synthesis, several unconventional methods, like sonochemical, microwave assisted combustion, spray pyrolysis, spray drying, laser pyrolysis, microemulsion, reverse micelle, and biosynthesis, are also presented. MFe2O4 (M = Co, Cu, Mn, Ni, Zn) nanosized ferrites present good magnetic (high coercivity, high anisotropy, high Curie temperature, moderate saturation magnetization), electrical (high electrical resistance, low eddy current losses), mechanical (significant mechanical hardness), and chemical (chemical stability, rich redox chemistry) properties that make them suitable for potential applications in the field of magnetic and dielectric materials, photoluminescence, catalysis, photocatalysis, water decontamination, pigments, corrosion protection, sensors, antimicrobial agents, and biomedicine.