Magnetic Properties Of Nanocrystalline Research Articles

Impact of Mn-substitution on crystallographic, optical, and magnetic properties of nanocrystalline Li-Ni-Zn ferrites fabricated by the sol-gel autocombustion technique

The wet-chemical sol-gel autocombustion, which is a faster and inexpensive synthesis technique has been implemented to synthesize Mn-substituted Li–Ni–Zn ferrite nanoparticles with nominal compositions of Li0.15Ni0.30-xMnxZn0.40Fe2.15O4 ranging from x = 0.00 to 0.15 in the step of 0.03. Well-shaped specimens have been sintered at temperatures ranging from 1373 to 1523 K. The patterns of the XRD reveal the internal shape which ensured the growth of the spinel layout for all samples. The Debye-Scherrer formula has been carried out to estimate the as-developed powder's crystallite size which is in the range of 46–52 nm. Both the lattice constant and average grain diameter of the samples have been increased with Mn2+ ions. The topmost value of the real portion of initial permeability and relative quality factor have been observed for Li0.15Ni0.18Mn0.12Zn0.40Fe2.15O4 ferrite sintered at the temperature of 1523 K, which are 7% and 16% larger, respectively, compared to the pristine composition.

Effects of Yttrium and Cerium co-substitution on Structures and Magnetic Properties of Nanocrystalline Nd-Fe-B Magnets

Cerium-containing (Ce) rare earth magnets with extraordinary cost-effectiveness are widely investigated around the world. However, when the concentration of Ce is much more, the kind of these magnets exhibits very poor thermal stability and overall magnetic properties. To weaken these disadvantages, we take eutectic YSUB50/SUBCeSUB50/SUB co-substitution alloys into account in this work. Magnetic properties, microstructures and metallurgical behaviors of (Y, Ce, Nd)-Fe-B magnets are systematically researched. For (YSUB50/SUBCeSUB50/SUB)SUB10/SUBNdSUB20/SUBFeSUB68.9/SUBBSUB1.1/SUB SPSed permanent magnets, good overall magnetic properties are HSUBcj/SUB = 725 kA/m, JSUBr/SUB = 0.73 T and (BH)SUBmax/SUB = 81 kJ/m³. It schematically depicts that coarse grain zones and fine grain zones occur during the spark plasma sintering (SPS) process. With the Nd content increasing, the deleterious CeFe₂ phases disappear. In addition, the volume fraction and width of coarse grain zones decrease. Ce-rich and Ce-lean regions are also observed in main phases, while Y and Nd elements are uniformly distributed. TEM results show that Nd and Ce are rich in the grain boundary and Y elements prefer to enter in 2:14:1 main phases. This work is favorable to a balanced utilization of high abundance rare earth elements in Nd-Fe-B magnets.

Prediction of Structural and Magnetic Properties of Nanocrystalline Mechanically Alloyed Fe-Ni Powders Using Multi-Gene Genetic Programming Approach

In this paper, a theoretical model based on multi-gene genetic programming (MGGP) approach has been applied to predict the structural and magnetic properties in nanocrystalline Fe–Ni powders prepared by mechanical alloying (MA) using a planetary ball mill. The MGGP model was used to correlate the input parameters (milling speed, chemical composition, and milling time), to output parameters (crystallite size and coercivity) of nanocrystalline Fe–Ni powders. The model obtained was tested with additional data to demonstrate its performance and prediction ability. The MGGP model is a robust and efficient method to find an accurate mathematical relationship between input and output data. A sensitivity analysis study was applied to determine the most influential milling parameters on the crystallite size and coercivity.

Structural and magnetic properties of nanocrystalline Ni0.7-xCuxCd0.3Fe2O4 prepared through Sol-gel method

A series of nanocrystalline Ni0.7-xCuxCd0.3Fe2O4 (0 ≤ x ≤ 0.5) are synthesized with the aid of an auto-combusted Sol-gel approach and then annealed at 700 °C. Rietveld refinement of X-ray diffraction (XRD) data reveals the cubic spinel phase of the samples with no impurity peaks. The average crystallite size of the materials is found to range from 18 to 29 nm and the mean particle's size is found between 51 and 69 nm. The variation in the lattice constant and volume of the unit cell with Cu content shows the increasing trend. The nanocrystalline nature of the investigated samples is revealed through Field emission electron microscopy (FESEM) and Transmission electron microscopy (TEM) analyses. The magnetic properties of the materials are characterized at room temperature by employing the Vibrating sample magnetometer (VSM) technique. The saturation magnetization and experimental magnetic moment are noticed to decrease up to 20% Cu substitution, thereafter both increase with Cu content. The observed M-H loops, the low values of remanence ratio (Mr/MS) and coercivity of the studied Ni-Cu-Cd materials suggest their soft ferrimagnetic behavior with the existence of multi-domain (MD) magnetic nanoparticles.

Magnetic Properties of Nanocrystalline (Nd,R)-(Fe,Co)-B (R = Pr, Ho) Alloys after Melt Spinning, Severe Plastic Deformation and Heat Treatment

Magnetic force microscopy (MFM) and magnetometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to study the magnetic and structural properties of the (Nd,Pr)-Fe–B and (Nd,Ho)-(Fe,Co)-B alloys. The alloys are synthesized using an arc or induction furnaces. The nanocrystalline state of the (Nd,Ho)-(Fe,Co)-B alloys is reached by two techniques, namely, melt spinning (MS) and severe plastic deformation (SPD). Hydrogenation and multistage treatment of (Nd,Ho)-(Fe,Co)-B alloys, which includes severe plastic deformation of melt-quenched ribbons and subsequent heat treatment, is also used. The surface morphology and domain structure of samples are studied. These pictures are used to interpret the observed magnetic hysteresis loops of the samples. It was found that multistage treatment allows one to obtain samples with higher values of coercivity due to the formation of a special microstructure with oval grain (the aspect ratio equal to ∼ 3).

Microstructure and magnetic properties of nanocrystalline Fe-Pt-based ribbons

The structural and magnetic properties of FePt – magnetic nanocomposites prepared by isothermal annealing of melt-spun Fe52Pt28Nb2B18 and Fe51Pt27Nb2B20 ribbons are reported. As it was evidenced the as-cast samples consists of L10-FePt hard magnetic grains dispersed in a predominant soft magnetic matrix composed of A1 FePt, Fe2B and boron-rich (FeB)PtNb residual phases. The applied annealing procedure reflects in temperature-induced structural and magnetic transition of dominated A1 FePt phase into L10-FePt dependent on Fe-Pt composition. As it was shown the Fe52Pt28Nb2B18 ribbon annealed at 700 °C exhibit promising hard magnetic properties at room temperature manifested as reasonably high remanence to saturation ratio (Mr/Ms = 0.68); coercivity (Hc = 0.92 T) and (BH)max = 83 kJ/m3 parameter. Strong exchange coupling between both FePt – based hard and soft magnetic phases was demonstrated by a smooth demagnetizing curve.

Effect of the partial substitution of FeCo by Ge on the magnetic properties of nanocrystalline (Fe0.8Co0.2)72.7Al0.8Si17.5Nb3Cu1B5 alloy

Nanocrystalline soft magnetic ribbons, with a composition of (Fe0.8Co0.2)72.7-xAl0.8Si17.5Nb3Cu1B5Gex (x = 0, 0.5, 1), were synthesized by melt spinning and subsequent crystallization. Special attention was focused on the microstructure, crystallization process and initial permeability. The crystallization process and microstructure were examined by using differential scanning calorimetry and X-ray diffractometry, respectively. The temperature dependence of initial permeability was presented in combination with the effect of the Ge substitutions. As a result, the Curie temperature of amorphous (Fe0.8Co0.2)72.7Al0.8Si17.5Nb3Cu1B5 alloy was enhanced by Ge addition, which implied improved soft magnetic properties at elevated temperatures. The (Fe0.8Co0.2)71.7Al0.8Si17.5Nb3Cu1B5Ge1 alloy annealed at 640 °C for 0.5 h exhibited superior magnetic softness at room- and high-temperatures with respect to the Ge-free alloy.

Annealing effect on structural, microstructural and magnetic properties of nanocrystalline Er-Co-B alloys for permanent magnet applications

Abstract In this paper, we have examined the structural, microstructural, and magnetic properties of Er-Co-B compounds. High-energy ball milling has been used to homogeneous the stoichiometric mixture of Er, Co and B as starting materials to synthesis the Er17Co75B8 powders. The samples are crystallized in the hexagonal CaCu5 - structure type with P6/mmm space group. Their structural and magnetic properties were assumed systematically as a function of annealing temperature. The structural properties were studied by means of X-ray diffraction and the microstructural properties via Scanning Electron Microscopy. The magnetic phase with abbreviated formula ErCo4.5B0.5 and global formula Er16.67Co75B8.33 was a dominate phase. These compounds exhibit a high coercivity of 8 kOe at room temperature for ErCo4.5B0.5 annealed at 1073 K for 1/2 h. These magnets with high HC are appropriate to permanent magnet applications. We have also applied to the Approach of Saturation in to Magnetization (ASM). The results were understood in according to the model of random magnetic anisotropy.

Structural and magnetic properties of nanocrystalline Zr-Co-Nb-Si-B rare earth free permanent magnets fabricated by spark plasma sintering

Abstract Rare earth free nanocrystalline Zr16Co78-xNbxSi3B3 (x = 0–3) bulk magnets were fabricated from melt spun ribbons with high density by employing spark plasma sintering (SPS) technique. The effect of SPS temperature on structural and magnetic properties was investigated. The hard magnetic Zr2Co11 phase which was present in the as-spun ribbons retained after SPS, indicating no phase decomposition. The magnetic properties were found to depend on consolidation temperature and Nb concentration. Optimum magnetic properties of coercivity of 3.3 kOe with saturation magnetization of 52 emu/g were obtained for x = 1 magnet consolidated at 600 °C. SPS magnets display a moderate magnetic texture and the coercivity mechanism is governed by combination of both domain wall pinning and nucleation of reverse domains.

Structural and magnetic properties ofNanocrystalline Nickel ferriteprepared byCitrate Sol–geland Solid- state reaction techniques

The structure and magnetic properties ofnanocrystalline nickel ferrite powder NiFe2O4 has been investigated using two different preparation methods, including the ceramic technique and citrate method. The synthesized powders were characterized using X-ray Diffraction (XRD) for crystallite size, X-ray density and lattice parameter calculation. The results indicated that the citrate method gives the lowest value for the lattice parameter and crystallite size (60.6 nm) in citrate method and (73.8 nm) in ceramic method. Distribution of cations among the two interstitial sites (tetrahedral and octahedral sites) has been estimated by analyzing the powder X-ray diffraction patterns by employing Rietveld refinement technique, and the results reveal the existence of samples asinverse spinelwith cubic structure and Fd-3m space group.The morphological investigations using Field Emission Scanning Electron micrograph (FE-SEM) and High Resolution Transmission Electron Microscopy (HR-TEM).The elemental analysis of samples usingEnergy Dispersive X-ray Analysis (EDAX) .Magnetic measurements of the samples at room temperature were carried out by means of vibrating sample magnetometer (VSM).

Local iron ion distribution and magnetic properties of the perovskites [formula omitted

The influence of thermal annealing on the structural and magnetic properties of nanocrystalline La1-xSrxFeO3-γ perovskites with x=0, 0.3, 0.4 and 0.5 was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy and magnetization measurements. Samples prepared by a sol gel method were calcined for 4 h at 1073 K and annealed for 8 h at 1273 K. XRD data indicate the formation of single phases in all samples, orthorhombic with the space group Pbnm for x = 0.0 and 0.3 and rhombohedral with the space group R3‾c for x = 0.4 and 0.5. The Mössbauer spectroscopy reveal that the sintering process increase the amount of Fe4+ and decrease the paramagnetic sites. Despite of the XRD data indicating the samples to be single phase, the higher coercivity observed in the samples with x = 0.4 may be associated with the emergence of Sr1-xLaxFe12O19 clusters in the samples. Irreversibility in the measurements of magnetization as a function of temperature was interpreted in terms of a high temperature glass cluster behavior.

Static and high-frequency magnetic properties of nanocrystalline Fe-Zr-N films

The phase and structural states of nanocrystalline Fe-based films alloyed with Zr and N, which were prepared by reactive magnetron sputtering under different conditions, magnetic-structure parameters of the films and their static and high-frequency magnetic properties have been studied. The interrelation of static magnetic properties and magnetic-structure parameters with the value of real effective magnetic permeability μ’ and frequency range, for which the value is unchanged, has been studied.

Magnetic Properties of the Nanocrystalline Nd-Ho-Fe-Co-B Alloy at Low Temperatures: The Influence of Time and Annealing

A study is made of the effects of various factors such as time (7 years), temperature, high magnetic field up to 580 kOe and heat treatment (HT) on the morphological structure and magnetic hysteresis properties of a high-coercive nanocrystalline (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy with a low temperature coefficient of remanence. We find a rather weak time effect on (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2. After 7 years, the loss in the maximum magnetic energy product (BH)max is no more than 5%. Annealing of the sample at 250 °C for 30 min decreases the amount of amorphous phase from 7.2 to 1.7%, while the grains’ size of the 2-14-1 phase increases from 83 to 109 nm. For the HT alloy, a magnetization jump is observed at H ~500 kOe. It can be attributed to the first-order magnetization process or a spin-flip magnetic transition. Rectangularity of the hysteresis loop degrades after annealing. In case of the short-time heat treatment, losses in (BH)max are ~10%.

Consolidation Behavior and Magnetic Properties of Nanocrystalline Nd-Fe-B Magnets Prepared by Spark Plasma Sintering

Spark Plasma Sintering (SPS) was studied as a means to consolidate Nd-Fe-B powders, previously subjected to grain refinement by HDDR (Hidrogenation–Disproportionation–Dessorption–Recombination). The sintering process was carried out under 60 MPa constant pressure, varying the maximum processing temperature from 500 °C to 900 °C with a holding time of 5 min. Densification was observed above 600 °C related to the melting of Nd-rich phase. The magnetic properties are clearly related to microstructure coarsening associated with the SPS temperature regime. A monotonic decrease for coercivity (Hcj) was observed as a function of maximum SPS operating temperature with values varying from maximum of 750 kA/m at 500 °C to less than 200 kA/m for SPS at 900 °C. Remanence (Br) and maximum energy product (BH)max showed optimum values for intermediate temperatures, since these properties benefit from the densification developed by SPS.

Influence of production technology on magnetic properties of nanocrystalline stacked and block magnetic cores

Influence of production technology on magnetic properties of nanocrystalline stacked and block magnetic cores

Thermal stability of magnetic properties of nanocrystalline (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy with induced magnetic anisotropy

The effect of nanocrystallizing annealing in the presence of an ac magnetic field (magnetic heat treatment) and tensile stresses (thermomechanical treatment), as well as in the presence of both tensile stresses and an ac magnetic field (complex thermomechanical magnetic treatment) on the magnetic properties of the nanocrystalline (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy and their thermal stability has been studied. It has been found that the nanocrystallization of the studied (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy in the course of magnetic heat treatment, thermomechanical treatment, and thermomechanical magnetic treatment at low tensile stresses (6–30 MPa) leads to about a threefold decrease in the coercive force, but does not ensure the thermal stability of magnetic properties at high temperatures. In nanocrystallization, in the course of thermomechanical treatment at 620°С for 20 min under tensile stresses σ = 250 MPa has been found to be optimum for the high-temperature application (up to 550°С) of the studied alloy.

Observation of enhanced magnetic pinning in Sm3+ substituted nanocrystalline Mn[sbnd]Zn ferrites prepared by propellant chemistry route

We report the effect of Sm3+ substitution on the structural and magnetic properties of nanocrystalline Mn0.5Zn0.5SmyFe2-yO4 (y = 0.00, 0.01, 0.03 and 0.05) samples prepared by propellant chemistry route using a mixture of fuels. Rietveld refinement of XRD patterns confirmed the formation of cubic spinel phase with space group Fd3¯m. The lattice parameter values decreased with Sm3+ substitution up to y = 0.03, but with a noticeable increase for the sample with y = 0.05. In all the samples, entire amount of Zn2+ and Sm3+ were found to be present at the A and B sites, respectively. A distribution of Mn2+ ions at the tetrahedral (A) and the octahedral (B) sites of the spinel Mn0.5Zn0.5Fe2O4 was observed. The microstructures of the samples were observed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). For all the samples, the average crystallite size decreased with increase in Sm3+ concentration, as determined using Williamson-Hall method. The FTIR spectra showed prominent absorption bands at ∼540 and ∼390 cm−1 corresponding to the stretching vibrations of the metal ion complexes at the tetrahedral (A) and the octahedral (B) sites, respectively. Magnetic properties such as saturation magnetization (Ms), remanence (Mr) and magneton number (ηB) were found to decrease, while the coercivity (Hc) and reduced remanence (Mr/Ms) of the samples were found to increase with increasing Sm3+ content. The increase in Hc with increase in Sm3+ concentration is interpreted as the enhanced pinning of the magnetic moments at the magnetic defects created by Sm3+ ions, which is further confirmed by Mössbauer spectroscopy through a nearly constant magnetic hyperfine field. This results in an increase in the magnetic particle size in spite of decreasing average crystallite size. Our work suggests that, Sm3+ substitution can be used to alter the magnetic hardness of MnZn ferrites and to enable them to be used as potential materials for various technological applications.

Magnetic structure and magnetic properties of nanocrystalline and amorphous Fe–Zr–N films

Data on the magnetic structure and magnetic properties of Fe–Zr–N films, which were prepared by reactive magnetron sputtering of a heated target and deposited on glass substrates, are reported. Depending on the Zr content (from 3 to 35at%), the film compositions are characterized by Zr-to-N (at%) ratio from 0.3 to 36.5. The magnetic properties (saturation magnetization Ms, coercive field Hc) and magnetic structure (effective local magnetic anisotropy field D1/2Ha, grain size 2Rc, effective anisotropy field of stochastic domain D1/2〈Ha〉, relative stochastic domain size RL/Rc) of the films are discussed in interrelation with their phase and structural states. The coercive field of the studied ferromagnetic nanocrystalline films was shown to obey the relationship Hc~(2Rc)6 and depends on not only the grain size but also the local magnetic anisotropy field D1/2Ha. As the grain size of ferromagnetic phase decreases, the contribution of the magnetoelastic component to the coercive field decreases. It was shown, by examples of weak ferromagnetic and superparamagnetic films with amorphous and mixed (amorphous+nanocrystalline) structures containing a nonferromagnetic phase, that the magnetic properties reflect the real structural and phase state of the films, which cannot be revealed by the X-ray diffraction analysis.

Improving Hard Magnetic and Magnetocaloric Properties of Nanocrystalline Intermetallics

ABSTRACTStructural and magnetic properties of nanocrystalline P6/mmm R(Fe,M)9C are presented. Their structure is explained with a model based on the R1–s(Fe,M)5+2s formula (s = vacancy rate) where s R atoms are statistically substituted by s transition metal pairs. The maximum coercivity is obtained for low Ga/Si content for auto-coherent diffraction domain size 30 nm. This controlled microstructure might lead to hard permanent magnet materials. Furthermore, the influence of small amount of Dy substitution on magnetocaloric properties of R-Fe systme is reported. The potential for using these low-cost iron based nanostructured RFe9 powders in magnetic refrigeration at room temperature is also discussed.

Influence of Magnetic Field Annealing Methods on Soft Magnetic Properties for FeCo-Based Nanocrystalline Alloys

Soft magnetic alloys have been widely applied to modern technology devices, such as transformer cores, choke coils and inductive devices. Magnetic field annealing can induce an uniaxial magnetic anisotropy K u [1-4] so as to improve the soft magnetic properties of alloys for the purpose of coping with different application requirements. So far, FeCo-based nanocrystalline alloys have been explored increasingly in order to improve the magnetic softness at higher temperatures[5-6]. Furthermore, the effect of magnetic field annealing on FeCo-based alloys is more pronounced compared with that of single ferromagnetic element composition [7-8]. Therefore, to explore the optimal magnetic field annealing method of FeCo-based alloys can effectively improve their soft magnetic properties to adapt to more strict application requirements at high temperature conditions. Magnetic field annealing of nanocrystalline alloy mainly includes three methods [9-11]. (a) The direct magnetic field annealing above the crystallization temperature of initial crystalline phase T x1 (magnetic field nanocrystallization). (b) Annealing above T x1 for nanocrystallization without magnetic field and then longitudinal magnetic field annealing below the Curie temperature of amorphous phase T c am. (c) After nonmagnetic field annealing above T x1 followed a magnetic field rean-nealing treatment under the same annealing condition. In order to achieve more superior magnetic softness of FeCo-based nanocrystalline alloys, the soft magnetic properties of nanocrystalline (Fe 1−x Co x ) 73.5 Si 13.5 B 9 Nb 3 Cu 1 (x=0.25,0.5,0.75) alloys under different magnetic field annealing were investigated.