Soft Magnetic Phase Research Articles

Tunable magnetic properties and magnetic domain structure of nanocomposite permanent materials via Ti addition into Nd-Fe-Co-B alloys

In this work, the effect of tunable Ti content on the microstructure, magnetic domain structure, and magnetic properties of as-spun and annealed Nd9.5Fe79-xCo5TixB6.5(x = 0,1,2,3,4) alloys at the quench speed of 18 m/s were investigated. For the as-spun alloy, augmenting the Ti content enhanced the initial crystallization temperature and the stability of the amorphous phase. Simultaneously, the incorporation of Ti led to augmentation in the quantity of nanocrystals within the amorphous matrix, thereby facilitating the formation of vortex-like magnetic domains with large size but reduced the saturation magnetization Ms. For the annealed alloy, the incorporation of Ti inhibited the precipitation of α-Fe phase, refined the grain, enhanced the exchange coupling between the soft and hard magnetic phase and facilitated the formation of smaller, more uniform vortex-like magnetic domains, These alterations were beneficial to improve the comprehensive magnetic properties. Furthermore, the addition of tunable Ti resulted in a remarkable impact on coercivity enhancement. The coercivity value exhibited a significant increase of 54.30%, surging from 374.24 kA/m to 577.51 kA/m. Upon a thorough analysis of the magnetic domains and coercive force mechanisms, it was ascertained that the introduction of Ti substantially augmented the creation of vortex-like domains. These domains effectively impede domain motion, consequently elevating the material's coercivity.

Study on the Microstructure and Magnetic Properties of Nd-Fe-B/Fe-Co Composite Nanowires.

To solve the problem of the low coercivity of Nd-Fe-B-based nanowires impeding their application in magnetic storage media, highly ordered Nd-Fe-B/Fe-Co composite nanowires were fabricated in an anodic alumina template by means of the alternating electrochemical deposition method. In this paper, the effect of soft and hard magnetic phase compositing on the magnetic properties of Nd-Fe-B-based nanowires was investigated, and the coercivity improvement mechanism was demonstrated. The results show that after annealing at 600 °C for 2 h, Nd-Fe-B/Fe-Co nanowires crystallize into a multiphase structure containing a hard Nd2(Fe, Co)14B phase and soft NdB4, NdB6, Fe7Nd, and Fe7Co3 phases. It is characterized that the Nd2(Fe, Co)14B phase preferentially nucleates, followed by NdB4 + NdB6 + Fe7Nd, while Fe7Co3 has been formed in as-deposited nanowires. The existence of a Nd2(Fe, Co)14B phase with high anisotropy fields, the remanence enhancement effect produced by exchange coupling between hard-soft magnetic phases, and the pinning effect between different phases make the composite nanowires approximately exhibit single hard magnetic phase characteristics with coercivity and remanence ratio as high as 4203.25 Oe and 0.89. The results indicate that synthesizing Nd-Fe-B/Fe-Co exchange-coupled composite nanowires via alternating electrodeposition is an effective way to optimize the magnetic performance of Nd-Fe-B-based nanowires.

Fabrication and application prospects of Pr–Fe–B/Alnico nanocomposite alloys

The potentials of rare earth-based nanocomposite alloys have never been realized due to strict microstructural constraints. Owing to the easy demagnetization it is challenging to increase the soft magnetic phase content. To avoid the easy demagnetization, Pr–Fe–B/Alnico magnets were fabricated and reported in this manuscript. The content of the Alnico phase is increased from 0 to 25 wt%, while the content of Pr element is reduced to below the sub-stoichiometry of the 2:14:1 main phase. The maximum magnetic energy product, which is the figure-of-merit for permanent magnets, is increased from 122 kJ/m3 for the standard alloy to 146 kJ/m3 for the alloy with 15 wt% Alnico which shows a significant improvement considering the fact that the Curie point of the magnet is also increased by ∼66 K. The special microstructure contains distinctly and heterogeneously distributed 2:14:1 and Alnico phases. The dimensions of neither the 2:14:1 nor the Alnico phases meet the dimensional requirements of the nanocomposite magnets, but still the smooth demagnetization curves are noted for the alloys. The behavior of effective anisotropy, the performance of the magnets in applied magnetic field and the magnetic interactions among the various constituent grains were quantitatively studied by reversible susceptibility, irreversible susceptibility and recoil loop openness. This study may provide some guiding principles for the development of nanocomposite magnetic alloys with excellent magnetic properties by using much less RE elements.

Micromagnetic study on Nd2Fe14B/α-Fe nanocomposite with inter-granular phase

The magnetic performance of hard-/soft-phase nanocomposites depends on their microstructure. Nanocomposites with an inter-granular phase, fabricated via a physical route, are fascinating as they can further enhance the magnetic properties of hard-/soft-phase nanocomposites. In this study, the magnetic performance is estimated on an isotropic Nd2Fe14B/α-Fe nanocomposite system with an inter-granular phase via micromagnetic simulation. The simulated results show that the magnetic performance of the system is strongly dependent on the size of Nd2Fe14B particles and the thickness of α-Fe phase. The simulated energy product provides a good approximation to the experimental one. The optimal size of Nd2Fe14B particles and thickness of the α-Fe phase, which give the highest energy product, are found. The simulation is expected to contribute to the preparation of high-performance isotropic Nd2Fe14B/α-Fe nanocomposite magnets with an inter-granular soft-magnetic phase.

Dependences of Magnetic Properties on the Grain Size and Hard/Soft Magnetic Phase Volume Ratio for Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe Nanocomposites.

The magnetic properties of magnetic nanocomposites consisting of hard and soft magnetic phases are dependent not only on the intrinsic properties but also on the grain structure and volume ratio of the two phases. In this study, we performed a systematic micromagnetic simulation on the magnetic properties of Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe nanocomposites. The volume fractions of the hard magnetic Nd2Fe14B or Ce2Fe14B phase were varied from 80% to 40%, and the grain sizes of the hard magnetic phase and the soft magnetic α-Fe phase were changed independently from 10 nm to 40 nm. The results show that when the grain size of both hard and soft phases is 10 nm and the volume fraction of the hard phase is 70%, the highest maximum magnetic energy product can be obtained in both Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe nanocomposites. The hard magnetic properties of Ce2Fe14B/α-Fe nanocomposite decrease significantly when the volume fraction of the α-Fe phase exceeds 30%. However, for the Nd2Fe14B/α-Fe system, this situation only occurs when the α-Fe volume fraction exceeds 40%. The reason for this is not only because of the low anisotropic field and the smaller exchange coupling length between the soft and hard magnetic phases, but also because of the lower saturation magnetization of the hard phase. The grain size has greater effects on the magnetic properties compared to the volume fraction of the hard magnetic phase. The main reason is that as the grain size increases, the remanence of the nanocomposite decreases sharply, which also leads to a rapid decrease in the maximum magnetic energy product. The simulation results on the effects of phase ratio and grain size have been verified by experiments on melt-spun Ce2Fe14B/α-Fe alloys with various compositions prepared by melt-spinning followed by annealing for various lengths of time. Due to the influence of demagnetization energy, the hard magnetic phase with high saturation magnetization is preferred for the preparation of high-performance nanocomposite magnets.

Microstructure and magnetic properties of Co82-(x+y)Zr13V5BxSiy melt-spun ribbons

The combined addition of Boron (B) and Silicon (Si) to the rapidly quenched Zr-Co ribbons on improvement of hard magnetic properties was investigated in Co82-(x+y)Zr13V5BxSiy alloy compositions which were annealed at various temperatures. The ribbons mainly contain rhombohedral Co5Zr phase and small amount of Zr2Co11, fcc-Co and cubic Zr6Co23 phases. The addition of small amounts of Boron (B) reduces the grain size effectively of the magnetic phases, and thus significantly increases coercivity. The introduction of Silicon (Si) into Zr-Co alloys contributes to an increase in the coercivity but results in slight decreases in the magnetization. It has been observed that with increase in annealing temperature beyond 650 °C, the amount of the soft magnetic phases (Co23Zr6 and fcc-Co) have increased, while the amount of hard magnetic Co5Zr phase is decreased. It has been observed that with increase in annealing temperature beyond 650 °C, the amount of the soft magnetic phases (Co23Zr6 and fcc-Co) have increased. High coercivity values were observed in all the ribbons annealed at 650 °C. Among all the ribbons prepared, the maximum coercivity of 6.14 kOe was observed in Co79Zr13V5B1Si2 ribbons annealed at 650 °C due to the formation of a high volume fraction of hard magnetic phase (Co5Zr) and homogeneous finer grains throughout the matrix. The achieved high BHmax value of 6.14 MGOe was measured for same composition annealed at 600 °C. Microstructural analysis have shown fine grains with average grain size of 140–180 nm in Co79Zr13V5B1Si2 ribbons annealed at 650 °C.

Spring exchange mechanism and temperature dependent magnetic properties of BaFe12O19/CoFe2O4 nanocomposites

Bare BaFe12O19, CoFe2O4, and their nanocomposites with concentration percentage 30–70, 50–50 and 70–30 were synthesized by sol–gel approach. The average crystallite size < D > of bare BaFe12O19 nanoparticles (NPs) was 35 nm which gets reduced with the addition of CoFe2O4 phase and found minimum for bare CoFe2O4 nanoparticles, i.e. 12 nm. Transmission electron microscopy (TEM) image showed the agglomeration of nanocomposites and mean particle size was observed to be 44 nm as estimated from normal size distribution. The ZFC/FC curves exhibited that the blocking temperature TB of all samples lies above room temperature. However, a small broad peak at ∼ 75 K in pure BaFe12O19 NPs is attributed to the surface freezing peak (Tf). The flatness in FC curve at low temperature with the addition of CoFe2O4 phase revealed the strong inter-particle interactions. From M−H loops, the value of saturation magnetization (MS) for Ba70/Co30 was found to be maximum (100.82 emu/g) than their corresponding bare nanoparticles. The higher value of MS showed the presence of exchange spring mechanism in these samples. The coercivity of BaFe12O19 sample was observed to be 4262 Oe which get increased with the addition of CoFe2O4 phase and found maximum for CoFe2O4 (7349 Oe), which shows the hard magnetic nature of CoFe2O4 NPs. However, the smaller value of Bloch’s constant “B” for BaFe12O19 phase (4.8 x10−6K-3/2) showed the strong intra-particle interactions in the core of BaFe12O19 NPs. The dM/dH vs. H curves showed the well-established exchange coupling of both hard and soft magnetic phases for 50% concentration of both phases and may be beneficial for high density recording devices.

Affable thermal treatment process to overcome the trade-off relation via interface engineering in an Fe-based amorphous film

As pre-eminent soft magnetic materials, Fe-based amorphous alloys have been extensively studied due to adjustable composition, low cost, and low iron core loss. The soft magnetic properties could be further improved after thermal annealing, which achieve a low coercive force (Hc) due to the low magnetic anisotropy and a high saturation magnetic flux density (Bs) on account of the precipitation of soft magnetic nanocrystalline phases. However, it is a key difficulty to control the nucleation and growth procedures of nanocrystals during annealing, resulting in rapid deterioration of Hc. Here, a soft magnetic Fe76Si8B13Nb3 film with ultra-fine amorphous/crystalline (a/c) core–shell structure is achieved from an amorphous precursor with the nanoscale phase separation. The pre-existing nanoscale phase separation provides vast nucleation sites and interphase boundaries, which could generate high concentration of nanocrystals and depresses the subsequent coarsening behavior even for long-time heat treatment. In consequence, the a/c core–shell soft magnetic film breaks the general trade-off relation in the soft magnetic material family with the highest Bs and lowest Hc simultaneously. This work provides a new perspective to design a/c alloys by amorphous precursor with dual phase structure, and importantly, it supplies effortless thermal treatment requirement to conveniently regulate the microstructures and soft magnetic properties of metallic glasses.

Broadband asymmetric transmission in quasiperiodic-metamaterials based on high entropy alloys ribbon

The new paradigm was introduced for achieving excellent electromagnetic (EM) waves absorption through multi-layer superimposed quasiperiodic-metamaterials, which were generated in rotary high entropy alloys ribbon. With the help of asymmetry, the designed anisotropic metamaterials with excellent absorption (ReflectionLoss≤−10dB) covered from 3.8 GHz to 18 GHz on the scale of sub-wavelength. High entropy alloys ribbon increased soft magnetic properties that design cascaded configuration metamaterials displayed distinct phase differences with increased rotation angle, which significantly focus on microwave attenuation. Meanwhile, the direction of the wave vector accompanied by rotation can realize polarized conversion, from linear polarizer to circular polarizer which is demonstrated in simulation, highly desirable in controlling EM waves and shrinking the size of traditional absorbing coating. Our study provides a fresh perspective to developing high-performance absorbers by combining soft magnetic and irregular phase patterns as possible as need for complex EM waves manipulations, arbitrary phase encoding, and vortex field.

Coercivity mechanism and long-range coupling of anisotropic Nd-Dy-Fe-Co-B/Fe composite thick film

In the present work, the long-range coupling between soft- and hard-magnetic layers and a dual enhancement of coercivity and polarization are achieved in anisotropic Nd-Dy-Fe-Co-B/Fe composite thick film with Ta spacer layers. It has been found that the coercivity mechanism dominated by the pinning mechanism is enhanced with increasing the periodic number of multilayers. The effect of the Ta spacer layer isolating the hard-magnetic phase grains leads to an increase in the coercivity. Continuous irreversible distribution confirms the coherent reversal of the soft and hard magnetic phases. The increase of polarization is caused by the dipole interactions acting in the long-range coupling between the layers.

Strategy of preparing SmCo based films with high coercivity and remanence ratio achieved by temperature and chemical optimization

SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system (MEMS). However, due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film, both the coercivity (Hc) and remanence (Mr) of films are difficult to enhance simultaneously. In this paper, SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process. The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed. By adjusting the Sm/Co atomic ratio from 1:5 to 1:4, Co soft magnetic phase disappears and the single phase SmCo5 is obtained, leading to the increase of coercivity of the films from 30 to 34 kOe. The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated. When the deposition temperature increases from room temperature to 250 °C, the coercivity will further increase from 34 to 51 kOe. However, a severe kink is observed in the demagnetization curves due to the poor exchanged coupling. An analysis of transmission electron microscopy (TEM) confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5, which contributes to the decoupling and low remanence ratio. Therefore, doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films. Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced. We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization, which can be utilized in high performed MEMS devices.

CoFe content-controlled magnetic exchange coupling in CoFe2O4-CoFe composites prepared by a simple and single-step sonochemical reduction method

CoFe2O4 and CoFe2O4-CoFe composites (with varied amounts of CoFe) are synthesized under atmospheric conditions by a simple single-step sonochemical method that enables easy control of CoFe content in the CoFe2O4-CoFe composites. X-ray and electron diffraction and high-resolution electron microscopy revealed the formation of CoFe2O4-CoFe composites. High-resolution transmission electron microscopy of CoFe2O4-CoFe composites showed the formation of core–shell type nanostructures. Therefore enhanced exchange coupling between soft CoFe and hard CoFe2O4 magnetic phases is observed. This work shows that the magnetic properties (saturation magnetization, coercivity, and remanent magnetization) of CoFe2O4-CoFe composites can be tuned as per requirement by controlling the content of soft magnetic phase CoFe and thereby, the exchange coupling between the hard magnetic phase CoFe2O4 and the soft magnetic phase CoFe can be tuned.

Novel method for preparation of high-performance SmFe12/α-Fe nanocomposite magnets by rapid thermal processing

SmFe12-based magnets have attracted considerable attention because of their high intrinsic magnetic properties. The metastable ThMn12-type SmFe phase can be easily decomposed into the α-Fe phase during heat treatment process. The nanocomposite theory of soft and hard magnetic phases is used to improve the magnetic properties of SmFe12-based magnets. At present, it is difficult to obtain strong exchange coupling in SmFe12/α-Fe nanocomposite magnets prepared by melt spinning or melt spinning followed by isothermal heat treatment. This study proposes a SmFe12/α-Fe nanocomposite magnet with a maximum energy product of 84.5 kJ/m3 by melt spinning followed by rapid thermal processing (RTP). The effects of RTP time on the phase composition, microstructure, and exchange coupling of the magnets were systematically studied. The results showed that a suitable RTP time benefitted the formation of fine and uniform 1:12 phase grains in the magnet. Henkel curves, magnetic domains and quantitative analysis based on the exchange coupling volume were employed to study the exchange coupling of the magnets, which indicated that the enhanced hard/hard-exchange coupling strength originating from the uniform and fine hard magnetic 1:12 phase grains is the main reason for the improvement in the overall exchange coupling strength. We believe this study provides a new technology for preparing high-performance SmFe12/α-Fe nanocomposite magnets with a high exchange coupling strength.

Novel Rare Earth (RE)-Free Nanocomposite Magnets Derived from L10-Phase Systems.

In the quest for novel rare earth (RE)-free magnetic materials, which also exhibit other additional properties such as good corrosion resistance and potential to operate at higher temperatures, an alloy deriving from the binary FePt system, with Mo and B addition, has been synthesized for the first time, using the out-of-equilibrium method of rapid solidification form the melt. The alloy with the composition Fe49Pt26Mo2B23 has been subjected to thermal analysis through differential scanning calorimetry in order to detect the structural disorder - order phase transformation as well as to study the crystallization processes. For the stabilization of the formed hard magnetic phase, the sample has been annealed at 600 °C and further structurally and magnetically characterized by means of X-ray diffraction, transmission electron microscopy, 57Fe Mössbauer spectrometry as well as magnetometry experiments. It has been proven that after annealing at 600 °C the tetragonal hard magnetic L10 phase emerges via crystallization from a disordered cubic precursor and becomes the predominant phase in terms of relative abundance. Moreover, it has been revealed by quantitative analysis via Mössbauer spectroscopy that the annealed sample exhibits a complex phase structure, where the L10 hard magnetic phase is accompanied by few other soft magnetic phases, in minority abundance: the cubic A1, orthorhombic Fe2B and residual intergranular region. The magnetic parameters have been derived from 300 K hysteresis loops. It was shown that, contrary to the as-cast sample which behaves as a typical soft magnet, the annealed sample presents strong coercivity and high remanent magnetization, accompanied by a large saturation magnetization. These findings offers good insight into the potential developing of novel class of RE-free permanent magnets, based on Fe-Pt-Mo-B, where the magnetic performance emerges from the co-existence of hard and soft magnetic phases in controlled and tunable proportions, capable of finding good applicability in fields requiring good catalytic properties and strong corrosion resistance.

Microstructure and magnetic properties of exchange-coupled nanocomposite Sm0.75Zr0.25(Fe0.8Co0.2)11Ti alloy

The preparation of ThMn12-type Sm-based permanent alloy with excellent magnetic properties has always been the focus of research. In this work, Sm0.75Zr0.25(Fe0.8Co0.2)11Ti alloys were prepared by arc melting followed by melt spinning, and then heat treatment at 800 °C for 5–30 min was conducted to optimize magnetic properties. Well exchange-coupled Sm0.75Zr0.25(Fe0.8Co0.2)11Ti alloy containing 1:12 phase and α-Fe phase was obtained successfully. With the increase of annealing time, the grain size is greatly increased from ∼30 nm of 5 min to ∼60 nm of 30 min, which is the main reason for the appearance of “kink” in the second quadrant demagnetization curve, and this can be confirmed by micromagnetic simulation. Moreover, the results from micromagnetic computation show that the magnetization vector of α-Fe phase has reversed at zero field in the coarse-grained model, but this reversal is not observed in the fine-grained model. The inconsistent reversal of hard and soft magnetic phases leads to the appearance of the “kink”.

Phase stability and coercivity in La2Fe14B magnet

Critical rare-earth free La2Fe14B (2:14:1) has the potential to be a gap permanent magnet. However, La2Fe14B decomposes into La, α-Fe, and LaFe4B4 phases below 1067 K. The phase stability and coercivity have been studied in La2Fe14B magnet using first principles DFT (density functional theory) calculation and micromagnetic simulation. For a perfect La2Fe14 B cube (edge length of 256 nm) without any structural defects and soft magnetic secondary phases, the coercivity (8.5 kOe) is reduced to ∼40% of its magnetocrystalline anisotropy field (HA = 20 kOe). Further, the coercivity sharply reduces to 3.2 kOe upon forming a thin layer (2 nm) of α-Fe on the surface of the La2Fe14B cube particle. The DFT calculations indicate that a partial replacement of La by other rare-earth (RE) elements can enhance the structural stability of 2:14:1. The gains in cohesive energy are 0.75, 0.10, and 0.33 eV per formula unit in (La0.5RE0.5)2Fe14B with RE = Ce, Pr, and Nd, respectively. Stabilizing the 2:14:1 structure and mitigating the formation of soft magnetic structural defects or impurity phases such as α-Fe is necessary to develop La2Fe14B based magnet, which can be moderately achieved via partial substitution of La by other rare earth elements such as Ce, Pr, and Nd.

Maximum energy product of exchange-coupled Sm(FeCo)12/α-Fe nanocomposite particle

The effects of the coating surface orientation of the α-Fe soft magnetic layer on the Sm(Fe0.8Co0.2)12 hard magnetic phase and the volume fraction of α-Fe, VFe, on the maximum energy product, (BH)max of exchange-coupled Sm(Fe0.8Co0.2)12/α-Fe nanocomposite magnet particles were micromagnetics OOMMF package was systematically investigated. The (BH)max of the reference model, Sm(Fe0.8Co0.2)12 particles without Fe layer, was 630 kJ/m3. In contrast, in the nanocomposite magnet particle model with soft magnetic layers on both sides of the hard magnetic phase, (BH)max reached a maximum value of 657 kJ/m3 at VFe = 12% (Fe layer thickness, tFe = 2 nm). In the model with α-Fe coating on the top and bottom surfaces of the hard magnetic phase, (BH)max = 636 kJ/m3 at VFe = 4% (tFe = 2 nm). Furthermore, the coating of the soft magnetic phase on both sides of the hard phase particles reduces the magnitude of the demagnetizing field, Hd of the nanocomposite magnet particles, indicating that the side coating of the soft magnetic phase is effective in increasing (BH)max. These findings allow for a greater degree of freedom in the design of nanocomposite magnets by adjusting not only the VFe volume fraction of the hard/soft phases but also their arrangement.

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.

Achieving Multiple-Resonance Permeability at Centimeter Waveband by Joint Strategies of Hard/Soft Exchange-Coupling and Selective Doping for Superior Microwave Absorption

With the prosperous development of radar technology and 5G communication, the microwave absorbing materials have become extremely crucial to improve the service life of weapons and working quality of equipment in modern society. However, it still remains a huge challenge to achieve broad absorption bandwidth at centimeter waveband due to the frequency-dependent quarter-wavelength matching thickness. In this work, the Ba(ZrNi)0.6Fe10.8O19/NiFe2O4 composites are proposed and prepared by an in situ sol–gel method. Herein, the hard/soft magnetic exchange-coupling and the selective doping strategies are dexterously integrated to achieve multiple-resonance permeability at centimeter waveband. In addition, by changing the ratio of hard and soft magnetic phases, the coupling effect is regulated to modify the multimagnetic resonance effect and optimize the absorption bandwidth. Finally, the maximum absorption bandwidth of the Ba(ZrNi)0.6Fe10.8O19/NiFe2O4 composites reaches (RL < −5 dB) to 8.6 GHz, exhibiting a promising prospect in centimeter-wave absorption.

Crystallization kinetics of Ti-doped Nd&lt;sub&gt;2&lt;/sub&gt;Fe&lt;sub&gt;14&lt;/sub&gt;B/α-Fe nanocomposite permanent magnets

Nanocomposite magnet consisting of a fine mixture of magnetically hard and soft phase has received much attention for potential permanent magnet development. One of the important requirements for alloys to exhibit excellent magnetic properties is a nanocrystalline grain size. The soft and hard magnetic phases can simultaneously achieve ideal nanoscale composites. The effect of Ti additions in the amorphous crystallization process of the exchange-coupled nanocomposite Nd&lt;sub&gt;2&lt;/sub&gt;Fe&lt;sub&gt;14&lt;/sub&gt;B/α-Fe magnet prepared by melt spinning is investigated. The results show that Ti can change the crystallization kinetics of the NdFeB melt-spun ribbons. The Ti can increase the activation energy of α-Fe and contrarily reduce the activation energy of a metastable 1∶7 phase, so the growth speed of α-Fe decreases and the metastable 1∶7 phase can stably precipitate from the amorphous phase. When the annealing temperature increases, a metastable 1∶7 phase is decomposed into the α-Fe phase and the Nd&lt;sub&gt;2&lt;/sub&gt;Fe&lt;sub&gt;14&lt;/sub&gt;B phase. The microstructure observation shows that the grains of the alloys doped with Ti are fine and uniform, with an average grain size of about 20 nm, and no particularly large α-Fe particles appear. The optimal magnetic property is (&lt;i&gt;BH&lt;/i&gt;)&lt;sub&gt;max&lt;/sub&gt; = 12 MG·Oe (1 G = 10&lt;sup&gt;–4&lt;/sup&gt; T, 1 Oe = 79.57795 A/m) when Ti addition is 1.0%.