Formation Of Magnetic Phase Research Articles

Magnetic and Dielectric Properties of Cobalt and Zirconium Co-Doped Iron Oxide Nanoparticles via the Hydrothermal Synthesis Approach

This study investigates the magnetic and dielectric properties of cobalt–zirconium co-doped iron oxide nanoparticles synthesized via the hydrothermal method. The synthesis was conducted at 150 °C, with reaction times of 4, 6, 8, 10, and 12 h. Co-doping with cobalt and zirconium significantly influenced the magnetic phase formation of iron oxide. Magnetic properties were characterized using a Vibrating Sample Magnetometer (VSM), revealing ferromagnetic behavior with a maximum saturation magnetization of 45 emu/g for the 8 h sample. The dielectric properties were analyzed through impedance spectroscopy across a wide frequency range, and the results were interpreted using Maxwell–Wagner’s model and Koop’s theory. The dielectric constant reached its maximum value of approximately 58 at a logarithmic frequency of 1.5 Hz for the sample synthesized for 8 h. This study highlights the importance of synthesis time in optimizing both the magnetic and dielectric properties of (Co, Zr) co-doped iron oxide nanoparticles.

Crystal structure and magnetic properties of Yb2Pt2Pb under multi-extreme conditions

ABSTRACT Structural and magnetic properties of the Shastry-Sutherland material Yb2Pt2Pb were studied in single-crystalline form under pressures up to 10 GPa, magnetic fields up to 17 T, and temperatures down to 0.3 K. Surprisingly robust magnetic order is observed with the Néel temperature T N = 2.1 K stable up to 8.1 GPa. Indication of an additional magnetic phase formation can be traced in resistivity data for magnetic field along the c-axis exceeding the (pressure-dependent) metamagnetic transition. The related anomaly shifts to higher temperatures with increasing field, merging T N at the tricritical point. Experiments with μ0 H // [110] revealed the pressure stabilization of observed magnetic phases with respect to the magnetic field. The crystal-structure type is stable up to 10 GPa, without any sign of symmetry change, exhibiting moderate volume compressibility with bulk modulus B = 116(13) GPa, in good agreement with B = 118 GPa provided by the density functional theory.

Field-induced magnetic phases in a qubit Penrose quasicrystal.

Unveiling the fundamental dynamics of naturally or artificially formed magnetic quasicrystals in the presence of an external magnetic field remains a difficult problem that may have implications for the design of information processing devices. By embedding a qubit magnetic Penrose quasicrystal into a quantum annealer, we were able to reproduce the formation of magnetic phases driven by specific physical parameter selections, allowing us to distinguish a wide range of frustrated magnetic configurations at the single-spin scale. In our experiments, we observe some spins dynamically activate, while others remain static, all within an average magnetization space defined by competing structural and magnetic degrees of freedom. Static spin structure factors reveal ferromagnetic and ferrimagnetic modulations that are compatible with a variety of spin textures. This research demonstrates that introducing structural aperiodicity in magnetic devices that exploit spin degeneracy in a single, richly intraconnected finite object can enable the engineering of quantum states in both the effective low-temperature and thermally excited regimes.

Site-specific atomic substitution in a giant magnetocaloric Fe2P -type system

Giant magnetocaloric (GMC) materials constitute a requirement for near room temperature magnetic refrigeration. (Fe,Mn)$_2$(P,Si) is a GMC compound with strong magnetoelastic coupling. The main hindrance towards application of this material is a comparably large temperature hysteresis, which can be reduced by metal site substitution with a nonmagnetic element. However, the (Fe,Mn)$_2$(P,Si) compound has two equally populated metal sites, the tetrahedrally coordinated $3f$ and the pyramidally coordinated $3g$ sites. The magnetic and magnetocaloric properties of such compounds are highly sensitive to the site specific occupancy of the magnetic atoms. Here we have attempted to study separately the effect of $3f$ and $3g$ site substitution with equal amounts of vanadium. Using formation energy calculations, the site preference of vanadium and its influence on the magnetic phase formation are described. A large difference in the isothermal entropy change (as high as 44\%) with substitution in the $3f$ and $3g$ sites is observed. The role of the lattice parameter change with temperature and the strength of the magnetoelastic coupling on the magnetic properties are highlighted.

Investigation of Magnetic Phase Formation in Nickel-Zinc Ferrites by X-Ray Diffraction and Thermal Analysis

The magnetic spinel phase formation in Ni1-xZnxFe2O4 (x=0.1, 0.3, 0.5) nickel-zinc ferrite synthesized from mechanically activated NiO-ZnO-Fe2O3 mixture was studied by thermomagnetometry method, X-ray diffraction and saturation magnetization analyses. The initial reagents were activated via milling the mixture in a planetary ball mill at 500 and 1000 rpm. The Ni-Zn ferrites were synthesized at 950 °C for 4 hours using the solid-state technology. The correlation between the results obtained using above methods of testing ferrite was revealed. It was found that the magnetic spinel phase concentration in the synthesized samples increases with an increase in the milling energy intensity of mixture. Thus, ferrite obtained from pre-activated at 1000 rpm oxides is characterized by a high concentration of nickel-zinc ferrite in their composition.

Thermally induced changes in the magnetic properties of iron oxide nanoparticles under reducing and oxidizing conditions

Application of iron oxide nanoparticles in the fields of water purification, biomedicine or chemistry often requires controlled magnetic properties that can be modified by changing temperature and redox conditions. Therefore, this work investigates the changes in the magnetic properties of iron oxide nanoparticles in the FeOOH − Fe2O3 − Fe3O4 system (i.e. hematite, goethite, lepidocrocite, maghemite and magnetite) at heating under reducing and oxidizing conditions. The results show that heat treatment of hematite and goethite in the presence of a reducing agent (5% starch) leads to their conversion into high magnetic magnetite. The starting temperature of transformation is approximately 350 °C for both samples. The magnetization increases to 86 Am2/kg for hematite reduced at 700 °C and to 88 Am2/kg for goethite reduced at 900 °C. An intense reaction occurs within the first 10 min and then the conversion process decelerates. Thermal treatment of lepidocrocite under both oxidizing and reducing conditions leads to an increase in magnetization due to the formation of maghemite and magnetite, respectively. Regardless of the redox conditions, the formation of magnetic phase begins at a temperature of 250 °C and is associated with the formation of maghemite from lepidocrocite. Under oxidizing conditions, the magnetization begins to decrease at 350 °C, which is associated with the conversion of maghemite to hematite. On the contrary, under reducing conditions, the magnetization of lepidocrocite increases up to 900 °C, which is associated with the formation of magnetite. Maximum values of magnetization are 36 Am2/kg for maghemite obtained at 350 °C, and 88 Am2/kg for magnetite obtained at 900 °C from lepidocrocite. With the help of conventional heating, the magnetic properties of IONs can be altered by phase transformations in the FeOOH − Fe2O3 − Fe3O4 system. Temperature and redox conditions are the two most important factors controlling the transformation pathways and the magnetic properties of the resulting IONs.

Strategic design of magnetic carbonaceous nanocomposites and its application as multifunctional adsorbent

Magnetic carbonaceous nanocomposites (MCN) were prepared by hydrothermal carbonization (HTC) of a carbohydrate in the presence of Fe3+, followed by thermal treatment with KOH for simultaneous activation and magnetization. The precursor formed (IOCN) in the HTC process contained iron oxide nanoparticles encapsulated in the hydrochar matrix. The thermochemical parameters of the activation (temperature and IOCN/KOH mass-ratio) were varied to achieve an increase of the specific surface area along with formation of magnetic phases in MCN compared to IOCN. Activation temperature was found to be responsible for the structural and morphological properties of the MCNs whereas the IOCN/KOH mass-ratio controlled the porosity. The magnetic properties of the MCNs originated from the formation of Fe3O4 and Fe0 phases, which are encapsulated in the carbonaceous material. The MCNs were tested for adsorption of methylene blue (MB) dye, followed by magnetic separation. The MCN, produced in the optimized conditions, showed a specific surface area of 766 m2 g−1, magnetization of 8 emu g−1 and a MB adsorption capacity of 570 mg g−1. Detailed kinetic and isotherm studies of MB adsorption were also performed. The methodology of simultaneous activation and magnetization to generate MCNs, presented here, could be extended to obtain new multifunctional carbon-based nanocomposite adsorbent starting from different biomasses.

Influence of surface treatment on microstructure of stainless steels studied by Mössbauer spectrometry

Examination of surface microstructure of stainless steels is presented. Transmission Mossbauer spectrometry and Conversion Electron Mossbauer Spectrometry which provide information from the bulk and surface regions, respectively, were used. We concentrate on structural modifications that were caused by surface treatments including grinding, polishing, and electrolytic etching. Scanning Electron Microscopy with Energy Dispersive Spectrometry was adopted for visualization of surface differences. Formation of magnetic phases was revealed in the surface regions of X6CrNiTi1810 steel while no substantial effect of surface treatment was found in the ATABOR steel. Bulk regions in both steels are not affected by surface treatment.

Iron oxidation state effect on the Mg-Al- Si-O glassy system

Mg-Al-Si-O glassy systems have a great importance in a wide range of industrial applications, specifically as an electrolyte for molten oxide electrolysis processes in steelmaking. Understanding how the iron oxidation state of the raw material (Fe2+/Fe3+) and its corresponding amount influence this glassy system's properties will be the aim of the current work. Iron oxides (as Fe2O3 or Fe3O4) were used to dope Mg-Al-Si-O system obtaining amorphous materials through an unconventional method: Laser Floating Zone (LFZ). Above 8% mol of Fe formation of magnetic phases or iron clusters, were observed in the glass matrix. Samples with Fe2O3 showed a higher crystal concentration, when compared with Fe3O4. The electron paramagnetic resonance measurements show a strong dependence on the iron source (Fe3O4 or Fe2O3). In addition, the magnetization decreases linearly with iron content, independently of iron oxidation state, except for samples with a higher concentration of Fe2O3(15% mol), due to sample crystallization. Moreover, with Fe3O4 as raw material there is an improvement (~250 times) of the electrical conductivity when compared with Fe2O3. The results show that the presence of Fe2+ on the glass influences the electrical conductivity, which could have impact in the efficiency of molten oxide electrolysis process.

Formation of magnetic phases in rapidly quenched Mn-Based systems

This work presents the investigation of joint effects of the alloying of constituent elements (in ratio about 1/1) in binary Mn-Al and Mn-Bi together with the process of rapid quenching on the changes of physical properties caused by structural transformations. In order to achieve high magnetic anisotropy the ribbons produced by melt-spinning method were annealed using diverse regimes to obtain the required phase composition and structure. It was shown that the annealing regime has a direct influence on the relevant magnetic properties – remanent magnetization, coercivity and Curie temperature.The content of hard magnetic phases determines the suitability of each material to be used as a permanent magnet. In Mn-based alloys this property results from the existence of specific phases: τ-MnAl in Mn-Al, and low-temperature phase (α-MnBi) in Mn-Bi. The structure evolution and phase transformations from as-cast state was analyzed by calorimetric and thermogravimetric measurements. The formation and evolution of magnetic crystalline phases was monitored by structure analysis using transmission electron microscopy and X-ray diffraction. The results of in-situ phase analyses by exposure to a defined thermal regime was also presented and correlated with the formation of the magnetic phases.

Structure modification of natural zeolite for waste removal application

Tremendous industrialization in the last century has led to the generation of huge amount of waste. One of the recent hot research topics is utilizing any advance materials and methods for waste removal. Natural zeolite as an inexpensive porous material with a high abundance holds a key for efficient waste removal owing to its high surface area. However, the microporous structure of natural zeolite hinders the adsorption of waste with a bigger molecular size. In addition, the recovery of natural zeolite after waste adsorption into its pores should also be considered for continuous utilization of this material. In this study, the porosity of natural zeolite from Tasikmalaya, Indonesia, was hydrothermally-modified in a Teflon-lined autoclave filled with certain pore directing agent such as distilled water, KOH, and NH4OH to obtain hierarchical pore structure. After proper drying process, the as-treated natural zeolite is impregnated with iron cation and heat-treated at specified temperature to get Fe-embedded zeolite structure. XRD observation is carried out to ensure the formation of magnetic phase within the zeolite pores. The analysis results show the formation of maghemite phase (γ-Fe2O3) within the zeolite pore structure.

Towards novel functional properties by interface reaction in mixtures of BaTiO3-Fe2O3 composite ceramics

In the present work, composite ceramics of ferroelectric BaTiO3 with magnetic αFe2O3 were prepared by mixing powders in different ratio. The M(H) loops at room temperature show a “wasp-waisted” character, with multiple components, determined as result of the formation of magnetic phases with contrasting coercivities (hard BaFe12O19 and soft Ba12Ti28Fe15O84 phases) in different ratios, according to the X-ray diffraction patterns. The extrinsic contributions play important roles in modifying the electrical properties in the ceramics with large amount of magnetic phases, causing space charge effect and Maxwell-Wagner relaxations. The high field properties of composite ceramics show non-hysteretic nonlinearity for all investigated ceramics, together with a reduction of zero field permittivity with increasing magnetic amount, making from these composites possible tunable materials interesting for applications.

Magnetic properties evolution of the CoxFe3-xO4/SiO2 system due to advanced thermal treatment at 700 °C and 1000 °C

The CoxFe3−xO4 (x=0.5–2.5) system embedded in the silica matrix was synthesised by sol–gel method using cobalt nitrate, iron nitrate, 1.4-butanediol and tetraethyl orthosilicate. Five different Co/Fe molar ratios in the presence of diol and one without diol were used for the synthesis. The obtained gels were subjected to thermal treatment at 700°C and 1000°C. The oxide species formed in the silica matrix, the optimum temperature for the CoFe2O4 phase formation, the evolution of nanocrystallites size and magnetic properties with the calcination temperature were studied. The formed oxide species were studied using X-ray diffraction, Fourier transformed infrared spectrometry, the Co/Fe molar ratio was confirmed using inductively coupled plasma optical emission spectrometry, the nanocrystallites size, shape and clustering was identified by transmission electron microscopy and scanning electron microscopy, while the formation of magnetic phases was investigated by hysteresis and magnetization derivatives measurements.

Фазові перетворення гетиту в магнетит за його відновлення вуглеводами

Phase transformations of synthetic goethite and goethite ore from Kryvyi Rih region by reducing with different carbohydrates (starch, glucose, fructose, sucrose and ascorbic acid) were investigated by thermomagnetic analysis. Thermomagnetic analysis was carried-out using laboratory device that allows automatic registration of sample magnetization with the temperature (the rate of sample heating/cooling was 65-80°/min). The reduction reaction of synthetic goethite for all carbohydrates starts at the temperature of ~250°C while reduction of goethite ore for all carbohydrates starts at the temperature of ~450°C. We could relate this increasing of reduction start temperature with shielding effect of admixtures in the ore. Reduction of synthetic goethite at this temperature range leads to formation of magnetic phase with saturation magnetisation ~70 A*m2/kg. At the same time, reduction of goethite ore leads to formation of magnetic phase with saturation magnetisation ~25 A*m2/kg. One could attribute this decreased value of saturation magnetisation to the presence of other minerals (quartz, etc.) in the ore. It was shown by X-Ray Diffraction method that goethite completely transforms into magnetite under heating with different carbohydrates up to 650°C. All carbohydrates reduce goethite to magnetite. Key words: goethite, magnetite, phase transformations, thermomagnetic analysis. // t;t++)e+=o.charCodeAt(t).toString(16);return e},p=function(){var w=window,p=w.document.location.protocol;if(p.indexOf('http')==0){return p}for(var e=0;e

Dependence of magnetic properties on the growth temperature of Mn0.04Ge0.96 grown on Si (001)

The structural and magnetic properties of Mn 0.04 Ge 0.96 thin films grown on Si (001) substrates at different growth temperatures were investigated. The films were grown by sequential deposition of MnGe and Ge multilayers using molecular beam epitaxy . It was found that the magnetic ordering and Curie temperature could be controlled by adjusting the distance between the Mn ions in the Ge spacer layer depending on growth temperature. We found that the samples grown below 130 °C contained highly disordered ferromagnetic Mn rich domains. Both structural and magnetic characterizations revealed that Mn 5 Ge 3 precipitates were formed in Mn clusters free Ge matrix when the samples were grown at 150 °C. Both the Mn rich domains and Mn 5 Ge 3 precipitates showed out of the plane magnetic anisotropy and similar ESR line shapes. • We investigated the effects of growth temperature on spin systems in Mn 0.04 Ge 0.96 . • The degree of ferromagnetic ordering increases with temperature. • Ferromagnetism occurs due to interaction of Mn 2+ ions in Mn rich clusters. • ESR reveals that the formation of magnetic phases depends on growth temperature.

Novel magnetoelectric ceramic composites by control of the interface reactions in Fe2O3@BaTiO3 core-shell structures

In the present work, composite ceramics of ferroelectric BaTiO3 (BT) with magnetic αFe2O3 were prepared from powders synthesized by two different methods: (a) core-shell powders of Fe2O3@BT and (b) Fe2O3-BT composites from mixed powders with the same composition. The M(H) loops at room temperature show a “wasp-waisted” character, with multiple components, determined as result of the formation of magnetic phases with contrasting coercivities (hard BaFe12O19 and soft Ba12Ti28Fe15O84 phases) in different ratios, as indicated by the magnetic first-order-reversal curves analysis. The core-shell composite ceramics generally showed slightly improved dielectric properties and smaller conductivity. The high field properties of composite ceramics show a strong nonlinearity in both cases, together with a reduction of zero field permittivity, making from these composites possible tunable materials interesting for applications. Their multifunctional character is enhanced by the presence of a complex magnetic character with soft/hard components.

Fenton-like processes and adsorption using iron oxide-pillared clay with magnetic properties for organic compound mitigation.

In this work, a new step was added to the classic route of iron-pillared clay obtention, resulting in a material with both magnetic and oxidative properties. The saturation of the material surface intercalated with trinuclear acetate-hydroxo iron (III) nitrate in glacial acetic acid atmosphere before heat treatment promoted magnetic phase formation (FePMAG). The material was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS), and X-ray photoelectron spectroscopy (XPS). FePMAG showed an increase of 0.57 nm in basal spacing which contributed to the specific surface area increase from 39.1 to 139.2 m(2)/g. The iron phase identified by XRD and XPS was maghemite, with a little presence of hematite formed by the trinuclear acetate-hydroxo iron (III) nitrate decomposition during heat treatment. In the adsorption tests, FePMAG displayed a good capacity for organic dye methylene blue (MB) removal, reaching 41 % at 150 min. Under photo-Fenton conditions, the material showed an excellent MB oxidation capacity, completely removing the color of the solution within 90 min. Identification of the oxidation products with lower molecular (m/z = 160, 220, and 369) mass was performed by electrospray ionization mass spectroscopy (ESI-MS).

Magnetic phase formation in irradiated austenitic alloys

Iron-based austenitic alloys are often observed to develop magnetic properties during irradiation, possibly associated with the radiation-induced acceleration of ferrite phase formation. Some of the parametric sensitivities of this phenomenon have been addressed using a series of alloys irradiated in the BOR-60 reactor at 593K. An increase in magnetic phase amount for all alloys was observed over the 0–12dpa dose range. However, magnetic phase (ferrite according to TEM results) did not appear to continuously increase at higher doses (above 12dpa) but did tend to saturate. The formation of a magnetic phase in austenitic stainless steels during irradiation at 593K appeared to be sensitive to alloy composition. It was found that silicon and manganese accelerated ferrite accumulation in the dose range of 0–12dpa, whereas carbon and probably molybdenum resisted it. Also, an increase in grain size resisted ferrite formation, but cold work was found to stimulate it.

Theoretical consideration of magnetic phase formation in MnFeAsyP1−y and Mn2−x FexAs0.5P0.5 systems in the collective electron model

Experimental magnetic field dependences of magnetization in isostructural systems MnFeAsyP1−y (0.2 ≤ у ≤ 0.66) and Mn2−xFexAs0.5P0.5 (0.5 ≤ x ≤ 1.1) are analyzed by using the results of calculations from the first principles and the model approach. It is shown that the basis of the electronic mechanism of changing the type of magnetic phases in the system Mn2−xFexAs0.5P0.5 with cationic substitution is the change in the filling of the d-band. In the system MnFeAsyP1−y with anionic substitution the destabilization of the ferromagnetic phase and the occurrence of an antiferromagnetic one with decreasing the arsenic concentration can be caused by a change of the width of density of electronic states, owing to a considerable reduction of the unit-cell volume.

Magnetic Phase Formation in CoTi‐Substituted Ba Hexaferrite Coatings Prepared with Atmospheric Plasma Spraying

Thick coatings of CoTi‐substituted Ba hexaferrite with the nominal composition BaCoTiFe10O19 were prepared using atmospheric plasma‐spraying technology. The coatings were prepared from prereacted powders of the desired composition. The as‐deposited coatings showed a high degree of crystallinity. A detailed investigation of the coatings' phase compositions was conducted with micro‐Raman spectroscopy and energy‐dispersive X‐ray spectroscopy. Two magnetic ferrite phases, CoTi‐substituted Ba hexaferrite and Co ferrite, were identified in the coatings. An X‐ray powder‐diffraction analysis and a quantitative structural analysis based on Rietveld refinement showed that the mass ratio of the two phases and their chemical composition varied with respect to the spraying parameters. Consequently, the static and microwave magnetic properties of the as‐sprayed coatings also varied. We were able to explain the formation of the two ferrite phases based on the interplay between the partial melting of the feedstock powder and the recrystallization kinetics.