Nanocrystalline Ferrites Research Articles

Correlation between grain size and carbon content in white etching areas in bearings

Premature failure of bearings during rolling contact fatigue is often associated with the formation of white etching cracks (WECs). Crack surface rubbing of WECs transforms the original bainitic/martensitic microstructure into white etching areas (WEAs), comprised of nanocrystalline ferrite. The grain size and carbon content vary within the WEA. Here, we show by atom probe tomography and scanning electron microscopy, that there is an inversely proportional relationship between grain size and carbon content in WEAs formed in 100Cr6 bearings that failed by WECs in service. We explain this phenomenon by the reduction of grain boundary energy through carbon segregation. Depending on the carbon content, this reduces the driving force for recrystallization and grain coarsening, thereby stabilizing the nanocrystalline microstructure. No such effect is observed for the substitutional element chromium. The smallest grain size (< 10 nm) is found directly next to decomposing cementite precipitates, which act as carbon sources, leading to carbon contents as high as ~9.5 at% in ferrite. Correspondingly, the WEA segments with the lowest carbon contents exhibit the largest grain sizes. Increasing carbon contents in sub regions of WEAs do not only lead to smaller grain sizes but also to higher average carbon contents at the grain boundaries as well as in the grain interior. Our results show that the mechanisms of ferrite microstructure stabilization through carbon grain boundary segregation shown in model experiments are also valid for the microstructure alterations associated with WEC failure occurring in practical bearing applications of the technical alloy 100Cr6.

Eco-Friendly Synthesis, TEM and Magnetic Properties of Co-Er Nano-Ferrites

Synthesis of Cobalt-Erbium nano-ferrites with formulation CoErxFe2-xO4 (x = 0, 0.005, 0.010, 0.015, 0.020, 0.025, and 0.030) using technique of citrate-gel auto-combustion was done. Characterization of prepared powders was done using XRD, EDAX, FESEM, TEM, AFM, and FTIR spectroscopy, VSM: magnetic properties, respectively. XRD Rietveld Analysis, SEM, TEM, and EDAX analysis studied spectral, structural, and magnetic properties. XRD pattern of CEF nanoparticles confirms single-phase cubic spinal structure. The structural variables are given by lattice constant (a), lattice volume (v), the average crystallite size (D) and X-ray density (dx), bulk density (d), porosity (p), percentage of pore space (P%), surface area (s), strain(ε), dislocation density (δ), along with ionic radii, bond length and hoping length were calculated. SEM and TEM results reveal the homogeneous nature of particles accompanied by clusters having no impurity pickup. TEM analysis gives information about the particle size of nanocrystalline ferrite, while EDAX analysis confirms elemental composition. The emergence of two arch-shaped frequency bands (ν_1 and〖 ν〗_2) that represent vibrations at the tetrahedral site (A) and octahedral site(B) was indicated by spectra of FTIR. The XRD Rietveld analysis confirms crystallite size lying between 20.84 nm-14.40 nm, while SEM analysis indicates the formation of agglomerates and TEM analysis indicates particle size ranging between 24nm-16 nm. The XRD Rietveld analysis confirms crystallite size lying between 20.84nm-14.40nm, while SEM analysis indicates the formation of agglomerates and TEM analysis indicates particle size ranging between 24 nm - 16 nm. The magnetization measurements indicated that increasing Er3+ content in cobalt ferrites decreases magnetization from 60emu/g to 42emu/g while coercivity decreases (18990) as compared to CoFe2O4 (18998) in cobalt ferrites with doping. The present study investigates the effect of different compositions of Er3+ replaced for Fe on structural and magnetic properties of cobalt ferrites.

Assessment of crystallographic and magnetic phase stabilities of cubic copper ferrite at shocked conditions

In recent years, dynamic shock wave-driven investigation carried out on the crystallographic phase stabilities of nano-materials has led to the accumulation of massive explosion of innovations which materialize in identifying the efficient materials so that such kinds of assessments are highly required before putting them into practical applications. Surprisingly, at shocked conditions, most of the materials are found to have undergone phase transition or a variety of changes have been observed in their stability as well as efficiency. Hence, device engineers are highly focused on the search of high shock-resistant materials for applications point of view especially for aerospace, defense, and military applications. In the present context, we have chosen one of the most familiar divalent metal ferrites of cubic copper ferrite nanocrystalline material (CuFe2O4 NPs) for the analysis of structural stability and the results have been screened by X-ray diffraction (XRD) as well as ultra-violet diffuse reflectance spectroscopic (UV-DRS) techniques. Magnetic phase stability has been evaluated by vibrating sample magnetometer (VSM). Interestingly, the title ferrite does not experience any crystallographic and magnetic phase transition even though it has polymorphic nature and variety of magnetic states. Therefore, it could be confirmed that CuFe2O4 NPs have considerable shock-resistant behavior for both crystallographic and magnetic phases. The results are discussed in the upcoming sections.

Evaluation of Harmonic Structure Obtained in Mechanically Milled Powders and Pulse Plasma Sintered Compacts of Austenitic Steel

The paper describes an attempt to obtain harmonic structure (HS) in AISI308L steel. Harmonic structure is the term related to the microstructure fabricated by mechanical milling of metallic powders under soft milling conditions, resulting in the formation of plastically deformed, grain-refined shell and unchanged core. This microstructure can be preserved after successful powder compaction. The powders of AISI308L steel were milled under soft condition up to 50 h and then compacted by pulse plasma sintering at 900–1100 °C. For powders and compacts XRD, SEM and hardness measurements were applied as characterization techniques. The milling process resulted in austenite transformation into nanocrystalline ferrite and formation of grain refined outer layer. The applied pulse plasma sintering parameters allowed preservation of this microstructure and manufacturing of compacts with homogeneous distribution of elements, relative density above 95% and hardness in the range 167–185 HV, depending on sintering temperature. Simultaneously, the starting phase composition was restored, i.e., austenite with 12% contribution of ferrite. The crystallite size of austenite was about 20 nm and was significantly smaller then in starting powders.

Nanocrystalline Ferrite (MFE2O4) For Photocatalysts and Thermal Properties by Homogeneous Co-Precipitation Technique

In this current research work, the preparation and properties of nickel ferrite nanoparticles were studied. Using nickel and ferric nitrates and citric acid, NiFe2O4 nanoparticles were prepared by a simple and cost-effective sol-gel auto-combustion method. The material used for this purpose was in the form of powder and also reagent grade chemicals were used for this manufacturing. Then the resultant powder was crushed into particles by using mortar and pestle. The phase formation of the NiFe2O4 was investigated by XRD and SEM techniques. X-ray diffraction (XRD) measurements were made it possible to approve the structural properties of the prepared samples. The morphology of these samples was explored through scanning electron microscopy (SEM). Thermal properties were studied by the thermal analyzer. The photocatalysts in an aqueous solution were studied under directly visible irradiation of the ferrite sample. After which the photocatalytic activity of the resultant product was observed by UV visible spectrometer.

Structural, electrical, and magnetic properties of Co-substituted Ni1- x Co x Fe2O4 (x = 0.1, 0.2, and 0.3) nanocrystalline ferrites

Nanocrystalline ferrites are interesting materials due to their rich physical and electromagnetic properties. In the present work, Ni1- x Co x Fe2O4 (x = 0.1, 0.2, and 0.3) nanocrystalline ferrites have been synthesized by solgel auto-combustion method and their microstructural, magnetic, and dielectric properties have been synthesized. The structural properties of synthesized ferrites are determined by using X-ray powder diffraction, scanning electron microscope, and Fourier transform infrared spectroscopy. The cation distribution obtained from X-ray diffraction shows that cobalt occupies only tetrahedral site in spinel lattice. The lattice constant of nickel ferrite increases with the increase in cobalt content. The structural parameters like bond lengths and tetrahedral and octahedral edges have been varied by cobalt substitution. The microstructural study carried out by using SEM technique showed that the average grain size increased with cobalt concentration. The initial permeability (μ i) increased with increasing cobalt concentration. The observed g-value from ESR is approximately equal to standard value. From hysteresis curve, the saturation magnetization (Ms), coercivity (Hc), and magnetic moment (μ B) are obtained as a function of cobalt concentration.

Multi-pass scratch test on pearlitic steel: Phase identification and crystallographic orientation analysis of the sub-surface layers

In this study, the abrasive wear of pearlitic steel was investigated, including the corresponding microstructural changes at the sub-surface. Multi-pass scratch tests were conducted under different conditions of normal load (4 and 18 N) and number of sliding cycles (from 1 to 12). Scanning electron microscopy (SEM) was employed to characterize the worn surface following the scratch tests. The microstructure after the tests was analyzed via focused ion beam/SEM, and electron backscattered diffraction (EBSD). A geometrically necessary dislocation (GND) analysis was utilized to evaluate the dislocation density from the EBSD data. The results facilitated the establishment of a relationship between the coefficient of friction (COF) and the test parameters. It was found that a decrease in COF was associated with an increase in the number of indenter passes while the COF was independent (statistically) of the normal load. During the multi-pass tests, the work-hardening behavior of the material controls the evolution of the microstructures beneath the scratch. The density of dislocations did not show any significant difference across the test conditions. The nano-hardness analysis showed the presence of a multi-layer with some microstructural transformation. The values of hardness obtained suggested the formation of nanocrystalline martensite in the topmost layer known as the white etching layer (WEL). The microstructure of the layer below the hard WEL is compatible with nanocrystalline martensite and saturated ferrite (based on the high hardness values). The third layer is characterized by nanocrystalline ferrite and partially dissolved cementite. No correlation was found between the crystallographic orientations prior to the tests and work hardening. The plastically affected region did not show any predominant crystallographic orientation.

Developed Process Circuit Flowsheet of Al Amar Ore for Production of Nanocrystalline Ferrite and Improving Gold Recovery.

Al Amar gold ore is rich in sulfides of base metals and is commercially applied for the production of copper concentrate via floatation and gold bullion by cyanidation of tailing. The current process flowsheet suffers from low gold recovery (∼60%) and loss of metals in the hazardous stockpiled residue. This work addresses these drawbacks by a newly experimental redesign of the process circuit. The innovative flowsheet comprises a sequence of operations, including acid leaching of the roasted ore, gold recovery from the leach residue, and preparation of a valuable zinc–copper–lead ferrite from the filtrate by coprecipitation followed by heat treatment. The ore is roasted at 650 °C and then leached in 20% HCl, where most of Zn, Cu, Pb, and Fe contents are dissolved, while pristine gold remains in the residue. Most of the gold (∼93%) can be recovered by cyanidation of the acid leach residue. Stoichiometric ratios of dissolved Zn, Cu, Pb, and Fe in the acid leach solution can be kept at 0.6:0.3:0.1:2.0, respectively, only by adding a small amount of ferric chloride. These metals are coprecipitated at varying pH values from 8 to 10, and the produced powders are annealed at temperatures from 600 to 1100 °C. X-ray diffraction (XRD) charts reveal sharp peaks of the targeted Zn0.6Cu0.3Pb0.1Fe2O4 phase at 600 °C, while a highly crystalline single phase is obtained at 1100 °C, independently of precipitation pH. The crystalline size of the produced powders increases with annealing temperatures (from 18–27 nm at 600 °C to 85–105 nm at 1100 °C). The finest size is found at pH 12. Scanning electron microscopy (SEM) investigation shows uniform cubic microstructures of samples annealed at 1100 °C. The produced ferrite powders exhibit soft magnetic characteristics. Saturation magnetization, Ms, substantially increases with pH. Coercivity, Hc, increases with increasing annealing temperatures, from 600 to 800 °C, and decreases above 800 °C. Preliminary cost–benefit analysis revealed that the profit margin of the proposed process flowsheet is promising. The wastewater is almost free of heavy metals. Our advances in high gold recovery and preparation of valuable magnetic nanocrystalline ferrite provide exciting opportunities to enhance and maximize Al Amar ore production for practical applications.

Influence of non-magnetic Zn-doping on the structural and the magnetic properties of magnesium ferrite

Spinel ferrites are the important class of soft magnetic material and are of interest to many researchers due to their excellent electrical and magnetic properties. Magnesium ferrite (MgFe2O4) is one such spinel ferrite with great potential technological applications. In the present study, the magnesium ferrite (Mg0.8Zn0.2Fe2O4) samples were prepared by well-known sol-gel auto-combustion method. The influence of Zn-doping on the structural and magnetic properties was investigated by X-ray diffraction and magnetization studies. The room temperature X-ray diffraction studies of the pure MgFe2O4 and Zn-doped Mg-Fe2O4 (Mg0.8Zn0.2Fe2O4) revealed the formation of single phase cubic spinel structure. The crystallite size obtained from Sherrer’s formula indicated that the Zn-doped and undoped shows nanocrystalline nature with crystallite size 22 nm and 24 nm respectively. The lattice constant (?) was found to be increased after Zn doping. Several other structural parameters are also increased after Zn doping. The magnetic properties were investigated by means of pulse field hysteresis loop technic. The M-H plot exhibits typical ferrimegnetic nature. The saturaturation magnetization increases after Zn doping. The observed magnetic behaviour of Mg0.8Zn0.2Fe2O4 nanocrystalline ferrite was on the basis of theoretical model.

Mechanism of cementite decomposition in 100Cr6 bearing steels during high pressure torsion

Severe plastic deformation leads to cementite decomposition in pearlitic and martensitic alloys, resulting in high-strength nanocrystalline ferrite. This effect can be employed to strengthen pearlitic wires but it can also be associated with material failure by white etching cracks (WECs) that are primarily known to concern bearings or rails. We investigate the decomposition of spheroidal cementite in the martensitic bearing steel 100Cr6 with 62 Rockwell hardness during high pressure torsion at 9.5 GPa applied pressure. The hard martensitic matrix and the even harder spheroidal cementite precipitates behave plastically very differently. The enforced macroscopic plastic deformation is almost entirely carried by the matrix. Plastic material flow of the matrix around the spheroidal cementite leads to wear of the spheroidal cementite as indicated by continuously increasing levels of chromium in the matrix. Plastic deformation of spheroidal cementite via dislocation gliding supposedly accelerates this process as slip steps generated thereby are preferential sites of wear at the matrix/cementite interface. Larger spheroidal cementite precipitates are more prone to plastic deformation and to decomposition than smaller ones. The mechanism likely holds true in general for multiphase materials with large strain difference between phases subjected to high pressure torsion. Although the formation of WECs in 100Cr6 bearings might be slowed down by reducing the size of the spheroidal cementite precipitates, it is unlikely that this could entirely prevent this failure mechanism.

Synthesis and magnetic properties of Ni0.5MgxZn0.5-xFe2O4 (0.0 ≤ x ≤ 0.5) nanocrystalline spinel ferrites

In this work, structural and magnetic properties of Ni0.5MgxZn0.5-xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) nanocrystalline ferrites synthesized via the co-precipitation method are reported. The ferrites are found to be at the nano-scale with sizes below 30 nm and seem porous in their general appearance. The structural properties were investigated using X-ray and Infrared (IR) spectra. X-ray Diffraction (XRD) patterns have been refined using the Rietveld method to find the lattice parameters. It was found that all these ferrites are a single-phase cubic spinel related structure belonging to the Fd-3m space group. Further, the positions, occupancy and Wyckoff's cationic position of the ions, in addition the lattice constant (a), the crystallite size (D) and the micro-strain of the composites have been analyzed and found to be affected by the variation of the Mg2+ ions concentration. The Vibrating Sample Magnetometer (VSM) technique showed that these nanoparticles are superparamagnetic with approximately impermanent magnetization of relatively high values. It was also found that the magnetization values of the Ni0.5MgxZn0.5-xFe2O4 (0.0 ≤ x ≤ 0.5) system increase with the existence of the Mg2+ and the Zn2+ contents together (at x = 0.1, 0.2, 0.3, 0.4) due to the increase in the super exchange interaction happening between the Fe3+ and the Ni2+ ions resulting from the occupation of the Mg2+ and the Zn2+ ions (nonmagnetic) to exclusively the A-sites as indicated by the Rietveld's structural analysis. These composites are expected to be promising for biomedical applications due to their superparamagnetic property below 30 nm.

Visualization of microstructural mechanisms in nanocrystalline ferrite during grinding

Microstructural changes in the near-surface regions of a material determine its mechanical properties and consequently also its tribological behavior. This work is a study of the microstructural development of nanocrystalline ferrite subjected to a grinding process using molecular dynamics simulations. We visualize the work piece by producing various types of computational tomographic sections that are colored according to the grain orientation, the local temperature, the stress in grinding direction, as well as the atomic flow velocities. In particular, we introduce “differential EBSD” tomographs to highlight the changes to the microstructure caused by the grinding process, allowing us to detect even subtle differences in lattice orientation and small distances in grain boundary migration. We use our visualization approach to discuss the acting microstructural mechanisms in a load- and time-resolved fashion, spanning a wide range of grinding conditions from mild to severe. In addition to removed matter, we observe lattice rotation originating at the surface and advancing deeper into the work piece with increasing load, grain growth by grain boundary migration, and the transient formation of unstable small new grains.

Analyzing the Microwave Absorption Properties of BaFe12O19, Ba4MnZnFe36O60 and NiFe2O4 Particles

A stoichiometric ratio of the Merck chlorides of Barium, Iron, nickel and NaOH as an agent was used to obtain the nano-crystalline ferrites (BaFe12O19, Ba4MnZnFe36O60 and NiFe2O4) by a combination of co-precipitation and high-energy reactive milling (RM) methods. After milling, the as-synthesized ferrite materials were exposed to a heat treatment at 1100°C for 4 h with the heating rates of 10°/min. After cooling the powders of ferrites inside the furnace, they were sintered at 1200°C for 4 h. The microstructural, structural, magnetic, and microwave absorption features were examined by x-ray diffractometry (XRD), scanning electron spectroscopy (SEM), vibrating-sample magnetometry (VSM) and network analysis (VNA), respectively. As can be seen in the hysteresis loops, both saturation magnetization and coercivity were changed by altering the ferrite kind. After sintering, the Ba-ferrites showed a smaller amount of saturation magnetization of 300 G (0.03 T) and a larger quantity of intrinsic coercivity 1.8 kOe (144 KA/m) compared to the Ni-ferrite and Ba4MnZnFe36O60. After sintering, the samples’ reflection loss spectra were changed and reached the maximum value of − 35 dB (at resonance frequency) for NiFe2O4, making it suitable␣for application in the microwave and resonance absorbers.

Nickel ferrite nanocrystalline as a green and recyclable catalyst for the synthesis of Spiro-oxindole-chromene

A separable NiFe2O4 nanocrystalline catalyst was synthesized via a simple co-precipitation method. The catalytic activity of this heterogenous catalyst was investigated to synthesize Spiro-oxindole-chromene derivates via Knoevenagel condensation, and Michael addition reaction under conventional heating condition. The catalyst showed a prominent catalytic activity in a good yield (86.74 %). This easily separated catalyst could be recycled efficiently for four cycles without significant loss of its activity. Furthermore, the products were investigated for the antioxidant activity using DPPH method. The IC50 of the compounds was found to be 182.3 ppm. The use of catalysts has been proven a simple, efficient and environmentally friendly reaction. Based on the results, it is known that the reaction could not be achieved without the presence of NiFe2O4 catalyst.

Synthesis and Characterization of Lanthanum doped Co-Zn Spinel Ferrites Nanoparticles by Sol-Gel Auto Combustion Method

Spinel ferrites nanoparticles play a significant role in our everyday lives. In the current work, La3+ doped Co-Zn ferrites with chemical formula Co0.5Zn0.5LaxFe2-xO4 (x = 0.00 to x = 0.2 with step size 0.04) was effectively prepared by sol gel technique. The formation of FCC spinel structure was confirmed by X-Ray diffraction (XRD) analysis. The average crystallite size were calculated to be in the 8 nm to 13 nm range. The lattice parameters were found to be decreased with the doping of lanthanum (La3+) contents. X- Ray density is analyzed to increase as the concentration of (La3+) doping increases, this is due to the fact that La3+ ion has a higher molar weight than Fe3+ ion. The spinel phase structure was affirmed by using FTIR.The two main absorption bands ?1 and ?2 are referred to tetrahedral stretching band and octahedral stretching band respectively, is found to be in the range of at around 400-530 cm-1. Spinel ferrites, such as Co-Zn spinel ferrites, have dielectric features that make them ideal for use in high-frequency applications. With new potential applications being investigated all the time. Physical properties, synthesis method, as well as sintering temperature and time, are all important factors in regulating the properties of dielectric materials. The dielectric features were measured in the frequency of 1 MHz to 3 GHz range. Lowered dielectric parameters studied across a higher frequency range recommend that such nano crystalline ferrites could be used to fabricate the equipment needed to perform at GHz frequencies.

Protective and Suppressing Electromagnetic Interference Properties of Epoxy Coatings Containing Nano-Sized NiZn Ferrites

Nano-crystalline ferrites with the chemical formula NixZn(1-x)Fe2O4, where x=0, 0.2, 0.4, 0.6, 0.8, 1.0, were synthesized using a co-precipitation method. The obtained ferrites were investigated by X-ray diffraction (XRD). The corrosion inhibiting behavior of nano-sized ferrites was tested using carbon steel samples and 10% aqueous ferrite extracts. Results were compared with previous data obtained for micro-sized ceramic ferrites. Nanoparticles show more favourable properties regarding inhibiting corrosion processes on steel. 2mm thick epoxy coatings on steel containing 10% vol. of nano-sized ferrites has been investigated as a microwave absorber. The microwave reflectivity of the coating was measured within the range from 6.5 to 15 GHz. Both the nano- and micro-sized ferrites included in the coatings exhibited different reflection loss spectra. The greatest attenuation on a level of 8-16 dB was observed. The nano-ferrite-filled epoxy coating exhibited a higher minimum reflection frequency in comparison with the micro-ferrite-filled coating. A frequency shift of 1-2 GHz was observed.

Synthesis, structural characterization, and magnetic properties of Ni–Zn nanoferrites substituted with different metal ions (Mn2+, Co2+, and Cu2+)

Three series of nanocrystalline Ni0.7-xZn0.3MxFe2O4 ferrites (M = Mn2+, Co2+, and Cu2+; x = 0.0, 0.1, 0.3, 0.5, and 0.7) have been synthesized using the citrate method. Several techniques have been used to investigate the influence of the different dopant ions and their doping levels on the structural and magnetic properties of the Ni–Zn ferrites. X-ray diffraction (XRD) analysis confirmed the creation of a single-phase spinel structure. The lattice parameter was found to increase with increasing Mn2+ and Co2+ ion concentrations, but was not altered by adding Cu2+. The density decreased with increasing concentrations of Mn2+ or Co2+, but increased with increasing Cu2+ content. The average particle size estimated from transmission electron microscopy (TEM) images was found to be in the range 21–41 nm, which revealed the manufacture of nanocrystalline ferrites. Two prominent fundamental absorption bands detected in IR spectra between 370 and 570 cm−1 can be ascribed to the intrinsic stretching vibrations of tetrahedral and octahedral complexes. The magnetic properties of the present spinel ferrites were measured by means of a vibrating sample magnetometer (VSM) at room temperature. The measurements showed that the saturation magnetization (Ms) for Ni–Zn–Mn ferrite increased from x = 0.0 to x = 0.3, but then decreased upon doping at x = 0.7, whereas a monotonic increase in saturation magnetization was observed for Ni–Zn–Co ferrite. For Ni–Zn–Cu ferrite, Ms decreased from 54.70 emu/g at x = 0.0–35.4 emu/g at x = 0.1 and then increased with further addition of Cu2+. The variation of Ms with different dopant concentrations can be explained on the basis of Néel's two-sublattice model. Among the investigated series, Ni0.7-xZn0.3CoxFe2O4 nanoferrites achieved high saturation magnetization and coercive field values, indicating that such compositions may find applications in the field of sensors.

Enhanced heating ability of Fe–Mn–Gd ferrite nanoparticles for magnetic fluid hyperthermia

This paper reveals the structural, magnetic and heating ability of citric acid coated Fe0.3Mn0.7GdxFe2−xO4 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) nanocrystalline ferrites. The synthesis of Gd-dope ...

Structural and electromagnetic studies of Mg1-xZnxFe2O4 nanoparticles synthesized via a sucrose autocombustion route

Mg1−xZnxFe2O4 nanocrystalline ferrites (1.0 ≥ x ≥ 0.0) were prepared using a sucrose autocombustion-assisted route. X-ray diffraction (XRD) showed secondary phase formation at Zn contents higher than x = 0.2. The obvious increase in the lattice parameters from 8.3937 to 8.4454 A upon increasing the Zn content might be attributed to the ionic radius of Zn2+ ions being larger than that of Mg2+ ions. The crystallite sizes calculated using Scherrer’s formula confirmed the nanocrystalline nature of the prepared samples. The Fourier-transform infrared (FTIR) spectra exhibited characteristic ferrite bands attributed to tetrahedral and octahedral sites, and there was an obvious splitting in the tetrahedral absorption band attributed to the Jahn–Teller distortion effect. Transmission electron microscopy (TEM) images showed agglomerated spherical particles with sizes that are in full agreement with results obtained by XRD. A reliable cation distribution was suggested based on the obtained structural parameters to address the preferential occupation of the entirety of the cations with increasing Zn content. The magnetic parameters estimated by vibrating sample magnetometer (VSM) measurements were utilized to confirm the suggested cation distribution and address the effect of Zn substitution on the entire system. All the investigated samples, except for ZnFe2O4, exhibited soft ferromagnetic characteristics. The obtained coercivities were higher than those reported in the literature and suggested the presence of an elevated demagnetization field and reflected the impact of the present synthesis method. The AC conductivity indicated semiconducting properties, and there was a ferromagnetic-to-paramagnetic magnetic transition in all samples with increasing temperature. The dielectric measurements also confirmed this transition by exhibiting relaxations in the same temperature range.

Probing the structural and magnetic properties of small crystalline nickel ferrite nanoparticles near the upper size limit of the single-domain regime

ABSTRACTNickel ferrite nanocrystalline particles were prepared by hydrothermal method. A systematic study was carried out on their structural and magnetic properties in wide ranges of temperatures and magnetic fields. The prepared nanoparticles were investigated by XRD, TEM, FTIR, and VSM. The results of Rietveld refinement revealed that the nanoparticles have a cubic single phase spinel type structure. The TEM measurements showed that the nanoparticles were monodisperse and spherical in shape. The FTIR results confirmed the single phase nature of the prepared nanoparticles. The magnetic measurements showed that the nanoparticles were ferromagnetic over a wide temperature range. The saturation magnetisation and the first anisotropy constant were observed to increase with reducing temperature. The estimated size of a single magnetic domain was found to be around 13 nm, which is three times smaller than the estimated crystallite size found from XRD, confirming that the average size of the nanoparticles was located above the critical size of the single-domain regime.