Hard Ferrites Research Articles

Influence of Dy3+ doping on Mössbauer, magnetic and microwave absorption properties of M-type Ba0.5Ca0.5DyxFe12-xO19 hexaferrites

The present research paper reports a systematic study of the magnetic, and structural properties of Ba0.5Ca0.5DyxFe12-xO19 M-type hexaferrite. The dysprosium was doped @ x = 0 − 0.2, keeping Δx = 0.05, in BCDF by the sol–gel self-ignition technique. The sintering of the synthesized samples was performed for 4 h at 1050°C. The crystallographic analysis of the samples was made from the X-ray diffractograms (XRD), while the morphological and elemental analysis was made from field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDAX) profiles. The structural results revealed the formation of the M-type hexaferrite having P63/mmc as a space group along with the co-existence of a secondary Fe2O3 phase. FESEM micrographs exhibit the hexagonal platelets randomly arranged with agglomerations at some places giving rise to the random variations in particle size with varying ’x’. Magnetic measurements (VSM) show that the saturation magnetization (MS) and coercivity (HC) increase with the increasing Dy3+ doping pointing towards the fact that the Dy doping in Ba-Ca ferrite can be used to fabricate the hard ferrites with good saturation magnetization. The Mössbauer spectrum recorded at room temperature reveals five superimposed sextets representing the five Fe3+ ion sites. Investigating the Microwave absorption (MWA) characteristics in the frequency range 8 − 12 GHz (X-band), reveals that the sample with x = 0.1 having 3 mm thickness possesses good MWA power. Its minimum RL value for matching frequency 10.06 GHz is approximately −26.96 dB, indicating that more than 90 % of microwaves are absorbed. The current work offers the Dysprosium-doped BCDF hexaferrites, as promising candidatesfor microwave absorption applications.

Exploring the effect of exchange coupling in (SrFe9.8Al2La0.2O19)1-x/(Co0.7Zn0.3Fe2O4)x nanocomposites synthesised by sol–gel auto combustion method

Extensive research has been conducted over the last decade to develop permanent magnets utilizing less rare earth materials. Exchange-coupled nanocomposite magnets are a fascinating development in the field of permanent magnets. They involve the combination of hard and soft ferrites, resulting in a unique and evolving magnet. Here we present an in-depth structural, morphological and magnetic characterization of ferrite-based nanostructures obtained through a bottom-up sol−gel approach. The combination of high coercivity of a hard phase SrFe9.8Al2La0.2O19 (SFALO) and high saturation magnetization of a soft phase, Co0.7Zn0.3Fe2O4 (CZFO), allowed us to develop exchange-coupled bi-magnetic nanocomposites by varying the mass percentage (x = 0, 0.1, 0.2, 0.3, 0.4, 1). Thermogravimetric analysis (TGA) up to 1200 °C was used to investigate the material’s thermal properties with the phase formation temperature. Detailed atomic/nano-scale structural characterizations of these nanocomposites were performed by X-ray diffraction and Transmission Electron Microscopy. The average particle size was calculated from the SEM analysis and it was observed that most of the composites with ratio x = 0.1, 0.3 & 0.4 was 145 nm and x = 0.2 was 165 nm. The Switching Field Distribution (SFD) curve revealed the exchange coupling between soft and hard magnetic particles. The findings indicate that the inclusion of a soft magnetic phase has a considerable impact on the exchange coupling between the hard and soft ferrite phases. As the spinel concentration increased, in the composite the saturation magnetization increased from 18 emu/g to 48 emu/g. From the stroner-wholfrathmodel, the decrease in the remanence ratio below 0.5 concludes the crystallites are randomly oriented. The nanocomposite with the ratio x = 0.1 was observed with the high magneto crystalline anisotropy of 2183.23 × 102 (J/m3) and a high energy product (BH)max of 5.5 kJ/m3. The aforementioned features of nanocomposites demonstrate their potential for use in permanent magnet applications.

Comparative investigation of magneto-fluorescent core@shell nanostructures prepared using hard and soft ferrite as core

The paper focuses on the potential of magneto-fluorescent nanostructures intended to join simultaneously several functions of dissimilar core and shell material into a single entity. Two different types of magneto-fluorescent nanostructures with a broad array of physicochemical properties are premeditated and collated here. Strontium hexaferrite (Hard ferrite) core with CdS shell and Nickel Zinc ferrite (Soft ferrite) core with CdS shell are the two sets of magneto fluorescent nanostructures that were designed. Magnetic and optical analysis of both sets provides divergent outcomes. The shape of the derivative hysteresis curve gives a direct indication of the dissimilar nature (superparamagnetic & Permanent magnetic) of magnetic cores respectively. Optical results depict that both sets of magneto-fluorescent nanostructures are highly stable showing emission only in the position of the CdS shell only.

Phase Separation of ϵ‐Fe2O3 and BaFe12O19 in a Synthesis Combining Reverse‐Micelle and Sol‐Gel Techniques

AbstractEpsilon iron oxide (ϵ‐Fe2O3) and magnetoplumbite barium ferrite (BaFe12O19) are well‐known hard ferrites. For one synthesis method of ϵ‐Fe2O3, combining reverse‐micelle and sol‐gel techniques, Ba ions are used to accelerate the formation of nanorod‐shaped ϵ‐Fe2O3. On the other hand, in synthesis of BaFe12O19 both Ba and Fe ions are used to form the final product. However, the coexistence of these two ferrites has not been reported by any synthesis. Herein, we investigated the effect of Ba ions on the final product for the synthesis combining reverse‐micelle and sol‐gel techniques. At a low Ba ion ratio of [Ba]/[Fe]=0.2, ϵ‐Fe2O3 nanorods are formed, while at higher Ba ion ratios ([Ba]/[Fe]=0.4, 1, 2), BaFe12O19 appears. The phase diagram at 1000 °C shows that at a Ba ion ratio of [Ba]/[Fe]=1, the ratio of ϵ‐Fe2O3 and BaFe12O19 is almost 1 : 1. The diagram shows intermediates between these two phases do not form, indicating a phase separation of ϵ‐Fe2O3 and BaFe12O19. During the sintering process of this synthesis, initially perovskite‐type Ba2Fe2O5 and γ‐Fe2O3 nanoparticles form. Then, in areas where γ‐Fe2O3 nanoparticles are gathered around Ba2Fe2O5 and react, BaFe12O19 is formed, whereas in areas lacking Ba2Fe2O5, ϵ‐Fe2O3 nanorods are formed within Ba‐ion containing silica glass.

Synthesis, characterization and microwave absorption properties of BaFe12O19/Ni0.5Mn0.5Fe2O4@ polyaniline nanocomposites with different ferrite percentages

AbstractIn this paper, BaFe12O19/Ni0.5Mn0.5Fe2O4@PANI core‐shell nanocomposites were synthesized with different ferrite/PANI ratios. The Ferrite nanoparticles were prepared by the auto‐combustion sol–gel method. Chemical oxidative polymerization of aniline in acidic solution along with adding ferrite nanoparticles to the composition was used for the synthesis of nanocomposites. The product then was studied by X‐ray diffractometer)XRD(, field emission scanning electron microscope (FE‐SEM), transmission electron microscope (TEM), and Fourier transform infrared spectroscopy (FTIR) analyses. The magnetic properties of samples were investigated with vibrating sample magnetometer (VSM). Also, nanocomposite samples were examined in terms of the ability to absorb microwaves. Using Vector Network Analyzer (VNA). the reflection loss (RL) of nanocomposites was measured at frequencies between 2 and 18 GHz. The minimum reflection loss (RLmin) was obtained at −36.98 dB at the frequency of 13.8 GHz with an effective absorption bandwidth of 4.87 GHz for the sample with the equal ratio of ferrite/PANI. Synthesized nanocomposite as an effective compound has very high reflection loss in a wide frequency range.Highlights Thermal stability is improved by adding ferrite nanoparticles to polyaniline. The polymer shell reduces the magnetic properties of ferrite nanoparticles. There is a strong exchange coupling between hard and soft ferrite. Ferrite/polymer ratio of 1:1 has the lowest amount of reflection loss. In the X and Ku band, magnetic loss is mainly caused by eddy currents.

Effect of rare earth doping on the electromagnetic response of hard ferrites SrFe12O19 for potential application in high-frequency devices

This work explores the synthesis, characterization, and potential application of rare earth doping on hard ferrites, focusing on their unique electromagnetic properties for potential applications in radio frequency (RF) devices. This study investigates the influence of rare earth (Sm+3) doping on structural and dielectric properties of strontium ferrite. Samarium doped strontium ferrite with composition Sr1-xSmxFe12O19(x = 0.0,0.1,0.2,0.3) is prepared using the sol-gel auto combustion technique. The prepared samples' crystal structural and morphological properties were studied using an X-ray diffractometer (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and RAMAN spectroscopy. XRD patterns of rare earth substituted strontium ferrite confirmed the formation of a hexagonal phase together with an impurity phase of Fe2O3 for x = 0.3. FTIR analysis establishes metal and Oxygen (M-O) stretching vibrations in Sr1-xSmxFe12O19 due to various interstitial sites in its structure. The Raman result shows the presence of four Raman active modes in prepared powders. Meanwhile, the broadening of Raman peaks with Sm2+ doping is also observed. Electromagnetic properties were obtained in the frequency region 2–18 GHz. An increasing tendency is observed in the real part of permittivity and permeability of all doped samples in the frequency region 2–18 GHz. The reflection loss was observed for sample x = 0.2 with the maximum value of > -40 dB at 18 GHz, and the adequate absorption bandwidth is 10 GHz from 8 GHz to above 18 GHz. On the basis of these results, among all prepared samples, Sr0.8Sm0.2 Fe12O19 is found to be the most suitable candidate for microwave absorbers.

Structure, magnetic, and electrodynamic properties of SrInxFe12‐xO4/Ni0.5Zn0.5Fe2O4 composites at low temperature

AbstractExchange‐coupled hard–soft bi‐magnetic ferrites can be used as isolators, microwave absorption materials, filters, hyperthermia materials, and biosensors with improved energy properties. The nanocomposites with the chemical composition SrInxFe12‐xO4/Ni0.5Zn05Fe2O4 (where x varies from 0.00 to 0.04) have the advantages of both materials: spinel and hexaferrite. The combination of Sr‐hexaferrate with spinel ferrite results in proximity effects, reversal of magnetization in two stages, and blocking temperatures that can be tuned in bi‐magnetic hard and soft ferrites. It was found an anomalius kink in the hysteresis loops and two peaks in the switching field distribution at x ≤ 0.02. The exchange interaction on the surfaces of hard and soft nanoparticles explains the behavior of the magnetic characteristics.

Strain and Exchange‐Spring Mechanism of (1‐x) Ni0.5Cu0.25Zn0.25Fe2O4 + (x) SrFe11Y1O19 Magnetically Soft–Hard Ferrite Composed Nanoparticles

AbstractA mixture of soft–hard (S–H) ferrites with the general chemical formula (1‐x) Ni0.5Cu0.25Zn0.25Fe2O4 (NCZFO) + (x) SrFe11Y1O19 (SFYO) is developed via sol‐gel auto‐combustion and their physical mixing. X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, field emission scanning electron microscopy (SEM) coupled with energy dispersive X‐ray spectroscopy, high‐resolution transmission electron microscopy (HRTEM), vibrating sample magnetometry (VSM) and two‐probe technique are used to examine the resultant materials. Rietveld refinement of XRD data confirms the co‐existence of both soft and hard phases in the composites. The HRTEM and FESEM results confirm the nanocrystalline nature of the synthesized particles. Williamson‐Hall method is employed to reveal the strain nature in soft and hard phases. VSM analysis shows considerable changes in the magnetic characteristics for the different composition of NCZFO and SFYO. The exchange‐spring mechanism is discussed in the manuscript.

Exploring 3D printing with magnetic materials: Types, applications, progress, and challenges

3D printing, also known as additive manufacturing (AM), represents a rapidly evolving technological field capable of creating distinctive products with nearly any irregular shape, often unattainable using traditional techniques. Currently, the focus in 3D printing extends beyond polymer and metal structural materials, garnering increased attention towards functional materials. This review conducts an analysis of published data concerning the 3D printing of magnetic materials. The paper provides a concise overview of key AM technologies, encompassing vat photopolymerization, selective laser sintering, binder jetting, fused deposition modeling, direct ink writing, electron beam melting, directed energy deposition and laser powder bed fusion. Additionally, it covers magnetic materials currently utilized in AM, including hard magnetic Nd–Fe–B and Sm–Co alloys, hard and soft magnetic ferrites, and soft magnetic alloys such as permalloys and elect­rical steels. Presently, materials produced through 3D printing exhibit properties that often fall short compared to their counterparts fabricated using conventional methods. However, the distinct advantages of 3D printing, such as the fabrication of intricately shaped individual parts and reduced material wastage, are noteworthy. Efforts are underway to enhance the material properties. In specific instances, such as the application of metal-polymer composites, the magnetic properties of 3D-printed products generally align with those of traditional analogs. The review further delves into the primary fields where 3D printing of magnetic products finds application. Notably, it highlights promising areas, including the production of responsive soft robots with increased freedom of movement and magnets featu­ring optimized topology for generating highly homogeneous magnetic fields. Furthermore, the paper addresses the key challenges associated with 3D printing of magnetic products, offering potential approaches to mitigate them.

Nanocrystalline alternative rare earth-iron-boron permanent magnets without Nd, Pr, Tb and Dy: A review

The continuous increase in the output of Nd-Fe-B permanent magnets leads to the increasing consumption of rare earth (RE) metals of Nd, Pr, Tb and Dy. As a result, a serious unbalanced utilization of RE resource occurs. To reduce the use of these critical REs, high abundance REs of Y, La, Ce and even Gd and Ho have been proposed to partly substitute Pr and Nd in sintered magnets and rapid-quenched nanocrystalline magnetic powders. Recently, the cost-effective RE-Fe-B magnets without Nd, Pr, Tb and Dy have also been developed. This type of magnet is preliminarily designed to bridge the magnetic properties gap between hard ferrites and bonded Nd-Fe-B magnets, which shows the potential applications in voice coil motor, spindle motors and magnetic resonance imaging systems. This review summarizes the progress of RE-Fe-B-type magnets containing no Nd, Pr, Dy and Tb based on the world-wide investigations and our recent findings. The fundamentals of intrinsic magnetic properties of Y, La, Ce based RE2Fe14B phases are introduced first. The relationship between magnetic properties and microstructure of rapidly quenched and bulk RE-Fe-B magnets with nanocrystalline structure is then emphatically discussed. Hard magnetic properties and performance/cost ratio of various RE-Fe-B alloy systems are summarized and compared. Furthermore, the current discoveries and the existing challenges are discussed. Some potential strategies for the future research in this field are finally proposed.

Fe30Co70/Co/CoxFe3−xO4-δ nanocomposite with multiple magnetic exchange resonance mechanisms and large magnetic loss available for microwave absorption application

Soft magnetic alloys are widely studied and reported as a type of important microwave absorption (MA) materials, while their magnetic losses are limited. In this paper, a multiphase composite strategy of the soft magnetic alloys, hard magnetic metals, and hard magnetic ferrites is adopted for increasing the magnetic loss. Then, three-phase Fe50Co50/CoxFe3−xO4-δ/γ-Fe2O3 (FC31), three-phase Fe30Co70/Co/CoxFe3−xO4-δ (FC22), and three-phase CoxFe3−xO4-δ/Co3O4/Co (FC13) nano-composites are prepared by a simple thermal decomposition process of FeC2O4 and CoC2O4 in vacuum. The crystal structure, surface composition, vibration of chemical bonds, morphology, micro-structure, and static magnetism are characterized by XRD, XPS, FTIR, Raman, SEM, TEM, and SQUID, respectively. The electromagnetic (EM) parameters are measured in 2–18 GHz by a vector network analyzer. Based on the measured EM parameters, the calculated magnetic loss tangents (tanδm) are over 0.5 in a wide frequency band of 8–18 GHz for the FC22/paraffin absorber, showing that the tanδm can be increased dramatically through the multiphase composite strategy. Benefiting from the increased tanδm, an effective absorption bandwidth of 7.0 GHz is achieved for the FC22/paraffin absorber at a thin thickness of 1.45 mm, exhibiting great application advantages in the MA field.

Life Cycle Assessment of Rare Earth Elements-Free Permanent Magnet Alternatives: Sintered Ferrite and Mn-Al-C.

Permanent magnets are fundamental constituents in key sectors such as energy and transport, but also robotics, automatization, medicine, etc. High-performance magnets are based on rare earth elements (RE), included in the European list of critical raw materials list. The volatility of their market increased the research over the past decade to develop RE-free magnets to fill the large performance/cost gap existing between ferrites and RE-based magnets. The improvement of hard ferrites and Mn-Al-C permanent magnets plays into this important technological role in the near future. The possible substitution advantage was widely discussed in the literature considering both magnetic properties and economic aspects. To evaluate further sustainability aspects, the present paper gives a life cycle assessment quantifying the environmental gain resulting from the production of RE-free magnets based on traditional hexaferrite and Mn-Al-C. The analysis quantified an advantage of both magnets that overcomes the 95% in all the considered impact categories (such as climate change, ozone depletion, human toxicity) compared to RE-based technologies. The benefit also includes the health and safety of working time aspects, proving possible reduction of worker risks by 3-12 times. The results represent the fundamentals for the development of green magnets that are able to significantly contribute to an effective sustainable transition.

The effect of the citric acid to metal nitrates molar ratio on the structural and magnetic properties of strontium hexaferrite nanoparticles synthesized by the sol-gel combustion method

Strontium hexaferrite is a hard ferrite with the chemical formula of SrFe12O19 and has a magnetoplumbite structure. Due to high anisotropy, high saturation magnetization, chemical stability, high corrosion resistance, and appropriate Curie temperature, it has been widely used as a permanent magnetic material. A novel sol-gel combustion process was used to synthesize ultrafine particles of strontium hexaferrite. The weight ratio of citric acid to the total weight of strontium and iron salts nitrate (CA/MN) is among the parameters affecting the purity of SrFe12O19 nanoparticles produced by the sol-gel method, which can improve the purity of the final product by controlling this parameter. M-type SrFe12O19 nanostructures with different citric acid to metal nitrates molar ratios (0.5, 1, 2, and 4) were prepared. The results showed that nitrate-citrate gels exhibit self-ignition behavior after combustion in the air at room temperature. The samples were then characterized by XRD, TGA/DTA, FTIR, FE-SEM, VSM. The results showed that the crystallite size of strontium hexaferrite is significantly affected by the molar ratio of citric acid to metal nitrates. As the molar ratio of citric acid to metal nitrates increases, the size of nanostructures decreases. By increasing the molar ratio of citric acid from 0.5 to 1, the saturation magnetization and magnetic remanence magnetization increase, but the coercive field decreases.

Semihard magnetic properties of TiFe2.5 iron-rich Laves phase and the effect of 4d- and 5d-element-substitutions for Ti

Rare-earth-free compounds exhibiting modest intrinsic hard magnetic properties may still yield viable permanent magnets if their constituent elements are abundant and inexpensive, and the properties are at least comparable to those of the hard ferrites. In this study, one such compound, the off-stoichiometric TiFe2.5 Laves phase with the hexagonal C14 crystal structure, was found to exhibit – in addition to the already known room-temperature ferromagnetism – a uniaxial, albeit weak, magnetic anisotropy. With a Curie temperature of 422 K, saturation magnetization of 55.3 Am2/kg and magnetic hardness parameter of 0.97 this semihard compound is just below the threshold for being of interest for the development into permanent magnets. Replacing a small fraction of Ti with the 4d Nb and Mo or with the 5d Ta or W increases the anisotropy field, but only below room temperature. Replacing Ti with Zr or Hf increases the Curie temperature and leads to a spin reorientation below 200 K. All these substitutions, as well as combined (Zr,W) and (Nb,W) substitutions, fail to improve the room-temperature intrinsic hard magnetic properties of the Fe-rich Laves phase. Furthermore, an attempt to develop a room-temperature coercivity through high-energy ball-milling yielded a value of 0.026 T, an unusually small 2.9% fraction of the anisotropy field. Defects inherent in the C14 crystal lattice may be responsible for the underperformance.

Enhanced magnetostriction of Co–Ni-ferrite composites derived from hard (CoFe2O4) and soft (NiFe2O4) magnetostrictive phases

We report on the enhanced magnetostrictive characteristics of composites derived from the hard cobalt ferrite (CoFe2O4; CFO) and soft nickel ferrite (NiFe2O4; NFO) materials. The CFO, NFO and CFO-NFO (CNFO) mixed composites (25NFO + 75CFO, 50NFO + 50CFO and 75NFO + 25 CFO) were synthesized by employing a cost-effective and eco-friendly glycine-nitrate autocombustion method. The CFO, NFO and their mixed composites were evaluated to assess their phase purity, surface morphology, magnetic properties, and magnetostrictive characteristics. The X-ray diffraction (XRD) and electron microscopy analyses revealed that the CFO and NFO nanomaterials were phase pure, porous in nature, and nano-sized with average crystallite size of 73 nm (CFO) and 69 nm (NFO). Subsequently, the Co–Ni-ferrite composite made from CFO and NFO in equal quantity by sintering at 1200 °C indicate that the lattice parameter, a, of the composite lies in between the lattice parameters of respective components (CFO-8.390 Å and NFO-8.343 Å) indicating that both phases co-exists as single-phase in the composite. The grains of the sintered compounds are nearly spherical shape with the average sizes ∼670 nm, ∼550 nm and ∼560 nm, respectively, for CFO, NFO and 50NFO +50CFO composite. Due to grain growth upon sintering, magnetizations of the sintered CFO and NFO nanomaterials are higher than that of as-synthesized samples. Interestingly, the magnetization curves of sintered CNFO composites exhibit symmetric nature (single loop), where their magnetization lies in between the magnetizations of NFO and CFO phases, indicating a proper exchange coupled between the two phases. The composites demonstrate better magnetostriction at lower magnetic fields than the parent sintered CFO and NFO samples. At an applied magnetic field of 2 kOe, the obtained magnetostriction value for 50NFO +50CFO composite (−120 ppm) is nearly 500% higher than that of CFO (−20 ppm) and 300% higher than that of NFO (−30 ppm). The structure-phase-property correlation established in these composites expected to provide a road-map for their possible applications in electromagnetic devices.

Examining the structural, magnetic and dielectric properties of exchange spring nanocomposite magnets comprising Ba0.5Sr0.5Fe12O19 and Zn0.5Co0.5Fe2O4

Exchange-coupled hard/soft ferrite nanoparticles are prospective to squeeze out a part of expensive magnets based on rare earth elements. However, the known exchange-coupled composite ferrite nanoparticles often suffer from the lack of a powerful hard core, high defective synthesis of magnetic phases and a poor interface between them. This work is featured by the use of highly coercive Ba0.5Sr0.5Fe12O19 magnets prepared by sol–gel combustion. Here in we demonstrate the synthesis of magnetic nanocomposites comprising Ba0.5Sr0.5Fe12O19 and Zn0.5Co0.5Fe2O4 hard/ soft ferrites by gradually increasing the share of spinel ferrites in the hard ferrites. Four samples of nanocomposites were prepared with the increasing order of hard ferrites using simple solgel auto-combustion method. Thermal breakdown examinations have been performed using TGA/DSC on the as-synthesised material from 0 °C to 1250 °C, and the temperature stability of the sample was detailed. The XRD analyses proved the presence of hexagonal and cubic crystal structure in each nanocomposite. Transmission Electron Microscopy was used to examine the morphology and topology of the nanocomposites. Hard and soft ferrites were detected in rod and non-spherical microstructures, correspondingly. The bending and the stretching vibrations in the sample was studied by using Fourier Transform Spectroscopy. The magnetic response of the synthesised samples was studied by using the Vibrating Sample Magnetometry. The prepared Nano powders displayed a highest coercivity Hc of 6307 Oe for pure hard ferrite while the pure spinel ferrite displayed a coercivity of 80 Oe. All the synthesized samples showed smooth M−H curves and single peak on dM/dH against H curves this indicates that complete exchange-coupled effects between the phases are achieved. The saturation magnetization increased with the increase in the content of spinel ferrite whereas the coercivity decreased with the increase in the spinel content.

Investigation of crystal structure and magnetic properties in magnetic composite of soft magnetic alloy and hard magnetic ferrite

The structural and magnetic properties have been investigated in the magnetic composites of hard magnetic Barium hexaferrite (BHF) and soft magnetic Ni–Mn–Sn Heusler alloy. The magnetic composites undergo two distinct ferromagnetic to paramagnetic and ferrimagnetic to paramagnetic phase transitions corresponding to alloy and BHF phases, respectively. Magnetic biasing between the hard and soft magnetic phases has been observed in the composites when both the phases are in the ferromagnetic ordering i.e., a squeezing in the magnetic hysteresis curve is observed around H = 0. The squeezing effect may be used in the magnetic memory device application where an optimum coercivity, high remanent magnetization, and high squareness ratio are required. On the other hand, the composites show high magnetocaloric effect with a constant high value of magnetic entropy changes between the two successive magnetic transitions. This gives an advantage with wide working temperature in the magnetocaloric application.

Hard ferromagnets as a new perspective on materials for thermomagnetic power generation cycles

We consider the ways in which magnetically hard materials can be used as the working materials in thermomagnetic power generation (TMG) cycles in order to expand the area in the magnetisation vs. applied field (M−H) plane available for energy conversion. There are 3 parts to this Perspective. First, experiments on commercially available hard ferrites reveal that, while these materials are not yet good TMG candidates, hard ferromagnets with higher thermal conductivity and a greater change of magnetization with temperature could outperform existing TMG materials. Second, computational results indicate that biasing a soft magnet with a hard ferromagnet is essentially equivalent to shifting the M−H loop by an amount proportional to the field of the biasing magnet. Work outputs under biased conditions show a substantial improvement over unbiased cycles, but experimental verification is needed. Third, we discuss the rationale for exploring artificial spin reorientation materials as novel TMG working materials.

Enhanced magnetic properties in Sm3+ substituted SrFe12O19

M- Type hexaferrite captivates researchers and industrialists for its diverse usage and applications in different fields such as permanent magnets, storage devices, recording media, radar absorbing materials and many more. In this work, Sm3+ substituted Strontium hexaferrite, Sr1-xSmxFe12O19 (x = 0, 0.05) is synthesized by using ethylene glycol aided sol–gel auto combustion technique. X-Ray Diffraction Technique is employed for the understanding of various structural features. Phase purity of the prepared samples is authenticated by performing Rietveld refinement method. All the studied samples crystallizes in hexagonal magneto-plumbite phase with P63/mmc space group. Crystallite sizes are determined using Scherer equation. Field Emission Scanning Electron Microscopy is used for morphological analysis. Average particle size decreases with Sm3+ substitution in comparison with parent one. Both field and temperature dependent magnetization measurements are accomplished for magnetic properties analysis. Hysteresis curves show Coercivity (Hc) value increases more than two times and saturation magnetization (MS) decreases slightly as compared to parent sample which clearly indicates that the sample can be used as hard ferrites. M−T measurements are carried out with the application of 500 Oe field. Both the sample show transition around 500 °C temperature. Substituted sample also shows a prominent Hopkinson peak in comparison with parent sample.

Exploring the structural, magnetic and magnetothermal properties of (CoFe2O4)x/(Ni0.8Zn0.2Fe2O4)1-x nanocomposite ferrites

The hard ferrite (CoFe2O4), soft ferrite (Ni0.8Zn0.2Fe2O4) and composite ferrite (CoFe2O4)x/(Ni0.8Zn0.2Fe2O4)1-x (hard/soft ferrite) with x = 0.2,0.4,0.6,0.8 were synthesized by sol-gel auto combustion method. X- Ray Diffraction analysis revealed the formation of the phases. The cubic structures of the samples were confirmed. The thermal analysis done using TGA/DSC confirmed the temperature of phase formation. The FTIR spectroscopy data for the samples were used to confirm the formation of functional groups and successful synthesis of the ferrites. The as-synthesized samples were characterized by SEM confirmed the overlapping spherical particles and elemental mapping was done with EDS. The FESEM and TEM analysis were done for the sample showing enhanced property of magnetic hyperthermia. The saturation magnetization (Ms), Coercivity (Hc) and the remanent magnetization (Mr) of the samples were studied using Vibrating Sample Magnetometry. The surface charge of the particles when dispersed in DI water was examined using Zeta potential measurement. Finally, we analysed the heating characteristics of the samples in an alternating magnetic field of frequency 350 kHz and field amplitude of 50 Oe. It has been concluded that the magnetic properties depend on the concentration of soft and hard ferrite in the samples and magnetic heating efficiency depends on the composition of the samples.