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Magnetic nanocomposite (hard) SrFe12O19-(soft) La(1-x) SrxMnO3 powders in 4:1 weight ratio was synthesized via a one-pot auto-combustion technique using nitrate salts followed by heat treatment in air at 950°C. Structural and morphological characterizations were performed via x-ray diffraction (XRD) and transmission electron microscopy (TEM). Vibra...
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Citations
... Some of the earlier investigations have also shown similar findings [60][61][62]. This decrease in the value of H c depicts that the materials got altered from domain wall pinning to nucleation wall pinning [63]. A high coercive field is caused by domain wall pinning rather than nucleation pinning. ...
Permanent magnets generate magnetic fields that can be sustained when a reverse field is supplied. These permanent magnets are effective in a wide range of applications. However, strategic rare-earth element demand has increased interest in replacing them with huge energy product (BH)max. Exchange-coupled hard/soft ferrite nanocomposites have the potential to replace a portion of extravagant rare earth element-based magnets. In the present, we have reported the facile auto-combustion synthesis of exchange coupled Ba0.5Sr0.5Fe10Al2O19 and Ni0.1Co0.9Fe2O4 nanocomposites by increasing the content of soft ferrite over the hard from x= 0.1 to 0.4 wt.%. The XRD combined with Rietveld analysis reflected the presence of hexaferrite and spinel ferrite without the existence of secondary phases. The absorption bands from the FTIR analysis proved that the presence of M-O bonds in tetrahedral site and octahedral sites. Rod and Non-spherical images from TEM represent the hexaferrite and spinel ferrite. Smooth M-H curve and single peak of SFD curve proves that the material has undergone a good exchange coupling. The nano powders displayed an increase in saturation magnetization and decrease in coercivity with the increases in the spinel content. The prepared nano composites were showing higher energy product. And the composite with the ratio x=0.2 displayed a higher value of (BH)max of 13.16 kJ/m3.
... The hexaferrite crystal structure contains five sites for the distribution of Fe 3+ ions: 12k, 4f2, and 2a (octahedral), 4f1 (tetrahedral), and 2b (trigonal bipyramidal) [25,26], with the last two sites having a spin-down [27]. Moreover, the results of the study indicate that Al 3+ ions prefer to occupy 12k, 2a, and 4f1 sites [28]. ...
This paper discusses the impact of Al ³⁺ ion substitution on Fe ³⁺ ions in the hexaferrite compound Ba 0.6 Sr 0.4 Fe 12-x Al x O 19 on the reflection loss value and bandwidth in absorbing microwaves. Hexaferrite Ba 0.6 Sr 0.4 Fe 12-x Al x O 19 (x = 0.25, 0.50, 0.75, and 1.00) was synthesized by high-energy ball milling (HEBM) for forty hours, followed by sintering at 1000°C in the air for five hours. Then, the crystal structure, formed phase, surface morphology, magnetization, and ability to absorb microwaves in the X-band region were successively characterized. All samples (x = 0.25, 0.50, 0.75, and 1.00) had a single phase with a hexagonal crystal structure. The particle size remained heterogeneous, ranging from 200 to 300 nm, with a platelet-like shape. The maximum amount of magnetic energy that could be absorbed by the material (M s ) increases from x = 0.25 to 0.75 and then decreases slightly for x = 1.00. The maximum value of reflection loss (RL max ) decreases as x increases. For x = 0.25, RL max is - 16.17 dB (f = 11.06 GHz) with a bandwidth of 3.56 GHz, whereas for x = 1.0, RL max is - 13.94 dB (f = 11.14 GHz) with a bandwidth of 1.68 GHz.
... [58]. For x = 0.0, 0.2, 0.6 and 0.8 value of H m comes out to be more than H c which affirms the presence of switching field distribution (SFD) [59].In x = 0.4 and 1.0 H m is found to be less than H c which may be due to the homogeneous structure of particles. Moreover, the height of the peak dM/dH at H ! 0 is observed to be lower than dM/dH at H ! H m . ...
The Co²⁺–Cr³⁺ ions substituted M-type hexagonal ferrites with composition Sr(CoCr)xFe12-2xO19\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(CoCr)_{x} Fe_{{\left( {12 - 2x} \right)}} O_{19}$$\end{document} (0.0≤x≤1.0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.0 \le x \le 1.0$$\end{document}) were prepared using the sol–gel auto combustion method. Prepared samples were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and Vibrating sample magnetometer (VSM). XRD affirms the establishment of a magnetoplumbite structure without the formation of a secondary phase. The crystallite size varies from 35.76 to 39.74 nm and FTIR analysis indicates the formation of SrM hexaferrite due to the presence of two prominent peaks in the range of 400–600 cm⁻¹. SEM micrographs exhibit the platelet-like structure. VSM analysis shows that coercivity and retentivity decrease non-linearly in substituted samples.
... The present values of M r /M s are in the range 0.12-0.19 which indicates the present ferrite nanoparticles are non-interacting under spin frustrations, which is consistent with the earlier reports [38][39][40]. The coercivity (H c ) of a single domain, non-interacting magnetic nanoparticles is given by relation [40]. ...
Sol-gel auto combustion technique has been adopted to prepare RE doped Mn–Ni–Zn ferrite systems following the stoichiometry Mn0.1Ni0.7Zn0.2RE0.5Fe1.5O4 (RE = Dy, Ce, Sm and Er). The XRD patterns confirm the cubic spinel phase with the Fd3m space group and the lattice parameter and crystallite size were found to be in the range of 8.3874–8.4066 Å and 28.6–33.2 nm. The M-H data indicates the soft magnetic behaviour of present ferrite systems. The substitution of rare-earth ions in the spinel structure influences the superexchange interaction and in turn, affects the magnetic behaviour of present ferrite systems. The highest value of saturation magnetization equal to 41.2 emu/g was reported for the sample with a composition of Mn0.1Ni0.7Zn0.2Ce0.5Fe1.5O4. For all the ferrite systems studied here the real part (ε′) of complex permittivity is increasing with an increase in frequency while oscillatory nature can be found in the imaginary part (ε″). The ε′ values can be found in the range of 5.421–5.856 at 8.2 GHz and it is 5.538–6.066 at 12.4 GHz. The ε″ values are in the range of 0.092–0.104 at 8.2 GHz while it is in between 0.042 – 0.105 at 12.4 GHz. A wavy nature can be seen in the real part (μ′) of complex permeability whereas the imaginary part (μ″) is decreasing for all compositions with the increase in frequency, but shows a weak resonance peak between 9 – 10 GHz. The μ′ values are in the range of 0.869–0.958 at 8.2 GHz and it is 0.903–0.925 at 12.4 GHz. The μ″ values fall between 0.269 – 0.334 at 8.2 GHz and it is in the range of 0.059–0.068 at 12.4 GHz. The microwave studies revealed that the present systems are working as microwave absorbers. The total effective shielding for all ferrite systems is in the range of 33.31–36.09 dB 8.2 GHz while it is in between 32.74 – 34.98 dB at 12.4 GHz. Under the investigation of shielding performance, it can be observed that all the RE doped Mn–Ni–Zn ferrites systems studied here can effectively suppress the electromagnetic interference in X-band frequency. The ferrite system with composition Mn0.1Ni0.7Zn0.2Ce0.5Fe1.5O4 has shown a potential microwave absorber in X-band frequency.
... Among the soft magnetic phases, magnetite (Fe 3 O 4 ) powder is an interesting soft magnet with a high saturation magnetization (M s ), a low cost, and high chemical stability, to be used as the soft magnetic phase in a ferrite-based exchange-coupled magnet [8,9]. Great efforts have been spent on increasing the BH max of strontium ferrite by combination with soft spinel cubic ferrite or metal alloys [10][11][12][13][14][15][16]. Moreover, different building blocks, as well as production techniques, are also utilized for the realization of large BH max [17,18]. ...
Nanocomposites consisting of strontium ferrite and magnetite are prepared to investigate the effect of exchange coupling between the hard and soft magnetic phases. Hexagonal strontium ferrite, SrFe12O19, synthesized using a solid-state route involving the sintering of precursors at 1000 °C gives a coercivity value as high as 3.73 kOe. An increase in the sintering temperature results in an increase in particle size and a decrease in coercivity. The soft ferrite phase Fe3O4 synthesized by a reverse co-precipitation method shows a saturation magnetization as high as 84 emu/g. Simple homogenous mixing of soft and hard components resulted in an exchange-coupled magnetic nanocomposite. With an increase in the soft magnetic content, the magnetization of the composite increases while the coercivity decreases. On sintering the nanocomposites at 1000 °C, coercivity remains intact even for an increasing soft magnetic content indicating an exchange decoupling between the soft and hard phases. This is attributed to the phase transformation of Fe3O4 to α-Fe2O3 at elevated temperatures.
... Therefore, to increase the capability of M-type hexaferrite material as a microwave absorber, several methods were carried out, for example combining Ba 2+ and Sr 2+ ions (Ba1-xSrxFe12O19) [6], substituting Mn 2+ ions on Fe 3+ ions (Ba0.6Sr0.4Fe12-zMnzO19) [4], making hexaferrite composites with perovskite (SrFe12O19-La1-xSrxMnO3) [7], BaFe12O19-NiFe2O4 composites [8], or making multiple layers consisting of BaFe12O19-BaCoZnFe10O19 composites [9]. ...
... Several sampling methods that have been used so far are co-precipitation [1,8], Salt Flux-Assisted [2], auto-combustion [7], mechanical alloying using milling [4,10]. Mechanical alloying method is the easiest and cheapest method. ...
... phase. Similar results were also obtained by J. N. Dahal et al., where the hexaferrite particle size was larger than the perovskite particle size [7]. The size of the particles formed is also influenced by the sintering temperature. ...
... Hence, it is assumed that there is no impurity (secondary crystal phases other than CZF and BHF) in the materials within the limitation of the XRD technique. The calculated average crystallite size (D) of BHF and CZF is found to be 36 nm and 26 nm, respectively, by using the Scherrer's formula [26,27]. The crystallite size of BHF is larger than CZF in whole composites, as enlisted in Table 1. ...
The composite of BaFe12O19 (BHF) and CoFe1.75Zn0.25O4 (CZF) with different weight percentages have been synthesized by using the high energy planetary ball mill technique. The obtained powders have been characterized by employing the X-ray diffraction, Field Emission Scanning Electron Microscope, and Energy Dispersive X-ray analysis techniques. The lattice parameters and phase percentage have been obtained by the Rietveld refinement analysis of XRD peaks. The crystallite sizes of BHF are greater than the CZF. The magnetic hysteresis loops have been recorded by using the Vibrating Sample Magnetometer (VSM) for all samples. The magnetic interaction between BHF and CZF in the composite has been investigated by plotting the loop width (ΔH) versus magnetization (M). The shape of these curves between loop width versus magnetization is changed with a different weight percentage of BHF and CZF. The saturation magnetization increases with an increase in the concentration of CZF in the composites. Vegard's law is used for comparing the theoretical and experimental magnetic parameters. The squeezing in hysteresis loops at H=0 vanishes for (55)% BHF + (45)%CZF sample below 150 K and interesting magnetic interaction between two phases has been observed.
... As a consequence, coercivity drops from H C = 358 kA m −1 for pure SFO to H C = 88,1 kA m −1 for 30 wt% Ni 0.6 Zn 0.4 Fe 2 O 4 ; while magnetization negligibly improves. Dahal et al [199] synthesize SFO/LaSrMnO 3 nanoparticulated composites with single-step reversal curves and supposedly good exchange-coupling between the phases, which may be the consequence of the small particle size. Although improvements in the remanence-to-saturation ratio are observed, unfortunately the magnetization of the soft phase is lower than that of SFO, leading to decreases in both coercivity and remanence in the composites. ...
Permanent magnets based on hard hexaferrite represent the largest family of magnets being used today by volume. They generate moderate remanence induction, but present crucial advantages in terms of availability, cost, resistance to demagnetization and corrosion and absence of eddy current losses. As a consequence, ferrites are the most logical candidate for substitution of rare-earths in selected applications that do not demand the best performing magnets. If the remanence of ferrite-based magnets was to be improved, even mildly, the door to a larger scale substitution could be opened. In this framework, we review here current strategies to improve the properties of hexaferrites for permanent magnet applications. We first discuss the potential of exploring the nanoscale. Second, progress related to controllably doping hexaferrites is revised. Third, results achieved by fabricating hard-soft magnetic composites using ferrites as the hard phase are presented. Finally, future prospects and new potential end applications for ferrite magnets are discussed.
... Therefore, in ferromagnetic materials, accurate calculation of the coercivity value is complicated [62]. According to the Stoner-Wohlfarth theory, coercivity is related to magnetic saturation [63]: ...
The structural and magnetic properties of La0.6−xYxSr0.4MnO3 (x=0-0.3) manganite synthesized by the sol-gel method was systematically investigated. The structural properties of the samples were investigated using X-ray diffraction (XRD) patterns and confirmed by Rietveld refinement analysis. Using the energy dispersive X-ray (EDX) analysis, the atomic percentage of the elements in the samples was confirmed. To investigate the surface morphology of the specimens, a field emission scanning electron microscopy (FESEM) analysis of the specimens was performed. The effect of yttrium substitution on the magnetic properties of the samples was also investigated. The Curie constant, magnetic moment, blocking temperature, and Curie temperature (Tc) were calculated using the Curie-Weiss law and the magnetic susceptibility of the samples.
... In modern technology, magnetic metal oxides are playing a prominent role because of their outstanding physical properties and potential applications in the area of nanoscience and nanotechnology [1,2]. For magnetism, due to relative high Curie temperature, excellent corrosion resistance, their low cost, high electrical resistivity and minor size with unique physical and chemical features, metal ferrites in their both forms; spinel ferrite (as soft) and hexaferrite (as hard) are talented for advanced permanent magnetic materials [3,4]. ...
This paper reports the synthesis, structural characteristics and magnetism of SrFe12O19/MCe0.04Fe1.96O4 (M = Cu, Ni, Mn, Co and Zn) hard/soft nanocomposites. The hard/soft compositions were manufactured via a one-pot reactions citrate sol-gel approach. The hard/soft phases formation was confirmed using XRD, SEM, TEM and HRTEM techniques. M vs. H (Magnetization measurements) were done at unbent temperature and 10 K. Smoothed M against H loops and single peaks in dM/dH vs. H curves were noticed in SrFe12O19/MnCe0.04Fe1.96O4, SrFe12O19/CuCe0.04Fe1.96O4 and SrFe12O19/ZnCe0.04Fe1.96O4 hard/soft nanocomposites. This indicated the manifestation of well exchange-coupled effect among hard and soft phases in these composites. However, SrFe12O19/CoCe0.04Fe1.96O4 and SrFe12O19/NiCe0.04Fe1.96O4 hard/soft nanocomposites showed non-well smoothed M against H loops and two peaks in dM/dH versus H plots, indicating that the dipolar interactions are unimportant compared to exchange-coupling behavior. Among all prepared nanocomposites, the SrFe12O19/MnCe0.04Fe1.96O4 hard/soft nanocomposite showed the highest exchange-coupling behavior. Microwave properties of the SrFe12O19/MCe0.04Fe1.96O4 (M = Cu, Ni, Mn, Co and Zn) hard/soft nanocomposites were investigated using coaxial method with applied frequency values fall between 2 and 18 GHz. Reflection losses were calculated from frequency dependences of the imaginary and real parts of permeability and permittivity. The correlation between the chemical composition of the spinel phase (A-cation) and microwave properties of composites. Most intensive electromagnetic absorption was observed for Ni- and Mn-spinels. This is can be a result of the differences in electron shell configuration and radii for A-site ions in the spinel phase. Change of the absorption mechanisms (transition from ionic polarization to dipole polarization) was observed.
