Excellent magnetic softness in TbFe/FeCoV multilayers

[Tb4oFe6o（x nm）/Fe49Co49V2（y nm）]N multilayers were prepared by multitarget magnetron sputtering using a rotary turn-table technique in a stop-and-go mode. The mulfilayers were investigated using X-ray diffraction, field emission scan electron microscopy and vibrating sample magnetometry. The result shows that the coercive field drops abruptly with increasing number of bilayers, and it remains generally stable when the number of bilayers is 10 or higher. An excellent magnetic softness with a coercivity of 1.0 mT is obtained for x = 5 and y = 5 after annealing at 250℃. A crystalline state is observed in FeCoV layers before and after annealing by X-ray diffraction.

Excellent magnetic softness-magnetization synergy and suppressed defect activation in soft magnetic amorphous alloys by magnetic field annealing

Fe-based amorphous alloys with high saturation magnetic flux density(B_(s))are increasingly attractive from both scientific and technological points of view,however,they usually suffer from the trade-off between magnetization and softness.In this work,we explore the soft magnetic properties(SMPs),magnetic and atomic structures,and defect activation during creep deformation of as-quenched and annealed Fe_(82.65-x)Co_(x)Si_(2)B_(14)Cu_(1.35)(x=0-20)amorphous alloys(AAs).Improved magnetic softness-magnetization synergy has been realized in all these alloys by field annealing.Particularly,superb SMPs with superhigh B_(s) of 1.86 T,low coercivity of 1.2 A/m and high effective permeability of 16300 are obtained in the Fe_(66.65)Co_(16)Si_(2)B_(14)Cu_(1.35) AA.The locally regularized arrangement of domains,homogenized structure with less structural/magnetic defects and suppressed crystal-like ordering by field annealing contribute synergistically to the superb SMPs.Besides,the relaxation time spectra obtained from creep deformation indicate less liquid-like and solid-like defects activated in the field-annealed AA,which is correlated with the structural homogenization and superb SMPs.This work provides new and comprehensive insight into the interplay among external field,heterogeneous structure,SMPs and defect activation of Fe-based AAs,and offers a promising pathway for softening amorphous alloys with high Bs.

Influence of iron powder content on the electromagnetic and mechanical performance of soft magnetic geopolymer composite

In the induction heating of airport pavement to remove snow and ice,soft magnetic geopolymer composite(SMGC)can be used to gather the dissipated electromagnetic energy,thus enhancing the energy utilization efficiency.The aim of this work is to analyze the influence mechanism of iron powder content on the electromagnetic and mechanical performance of SMGC,so as to provide theoretical guidance for the design of soft magnetic layer within airport pavement structure.The results show that the increase of iron powder content reduces the resistance and magnetoresistance of SMGC by decreasing the content of non-magnetic phases between iron powder.However,the reduction of iron powder spacing also provides a shorter transmission path for the inter-particle eddy currents in the SMGC specimen,which enhances the exchange coupling between iron powder,thus increasing the electromagnetic loss.Therefore,the compatibility between magnetic permeability and electromagnetic loss should be considered comprehensively in the mix design of SMGC.In addition,although iron powder can enhance the mechanical properties of SMGC by improving the density of geopolymer matrix,the excessive amount of iron powder can lead to a weak interfacial transition zone between geopolymer matrix and iron powder.According to the induction heating results,optimized SMGC can improve the energy transfer efficiency of induction heating by 24.03%.

Sodium Nitrate Passivation as a Novel Insulation Technology for Soft Magnetic Composites

Sodium nitrate passivation has been developed as a new insulation technology for the production of FeSiAl soft magnetic composites (SMCs). In this work, the evolution of coating layers grown at different pH values is investigated involving analyses on their composition and microstructure. An insulation coating obtained using an acidic NaNO_(3) solution is found to contain Fe2O_(3), SiO_(2), Al2O_(3), and AlO(OH). The Fe2O_(3) transforms into Fe3O4 with weakened oxidizability of the NO_(3)– at an elevated pH, whereas an alkaline NaNO_(3) solution leads to the production of Al2O_(3), AlO(OH), and SiO_(2). Such growth is explained from both thermodynamic and kinetic perspectives and is correlated to the soft magnetic properties of the FeSiAl SMCs. Under tuned passivation conditions, optimal performance with an effective permeability of 97.2 and a core loss of 296.4 mW∙cm−3 is achieved at 50 kHz and 100 mT.

Experimental research based on a C-band compact transit-time oscillator with a novel diode loading an embedded soft magnetic material and shielding structure

In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shielding structure is proposed.The soft magnetic material is designed to enhance the local magnetic field in the diode region.Moreover,the diode applies a shielding structure which can reduce the radial electric field.From simulation research,it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode.Through simulation research,it is verified that the diode can increase the conversion efficiency of the transit-time oscillator(TTO)from 30%to 36.7%.In our experimental study,under the conditions of a diode voltage of 540 kV and a current of 10.5 kA,the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied.The corresponding conversion efficiency is improved from 20.0%to 26.6%,which is 6.6%higher than that of a device loaded with a conventional diode.Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field,and contribute to the miniaturization and compactness of high-power microwave devices.

Effect of seed layers on the static and dynamic magnetic properties of CoIr films with negative effective magnetocrystalline anisotropy

The c-axis oriented hcp-Co_(81)Ir_(19)magnetic films were prepared on different seed layers(Ni,Cu,Ir,Pt,Au,and No seed).We systematically investigated the impact that surface-free energy and strain energy have on the orientation and defects and/or internal stress of the grains by increasing the lattice mismatch ratio.Moreover,the initial permeability and the natural resonance frequency were discussed in great detail using a comparison between calculated values and experimental values.We found that the almost unchanged 4πM_(s) andμ_(i) are not affected,while the changed H_(c),intrinsic K_(grain),and f_(r) are strongly dependent on the seed layer and seed layer material.Moreover,the extracted damping constant is sensitive to the defects and/or internal stress and orientation of the grains.Therefore,the soft magnetic properties and microwave properties are adjusted and optimized by seed layers with different materials.

Influence of Phosphorus Content and Magnetic Annealing on Soft Magnetic Properties of Electrodeposited Amorphous FeMnP Alloy Films

In this work, we investigated the influence of phosphorus and magnetic anneal on the soft magnetic properties of electrodeposited FeMnP alloy films prepared by changing sodium hypophosphite concentrations. X-ray diffraction radiation patterns showed an amorphous structure of electrodeposited alloy films. The saturation magnetization and coercivity value decreased from 586 emu/cc to 346 emu/cc, and 52 Oe to 18 Oe, with the P content increased, respectively. The absorption resonance peak became broad as the P content increased, and the natural resonance frequency decreased from 1.8 GHz to 0.6 GHz, with the P content increasing. Magnetic annealing of samples reduced the magnetic damping, and natural resonance frequency increased by about 1.8 GHz and 3.5 GHz for the sample with lower and higher P content. The film structure with lower P content changed at 300˚C, while the structure remains unchanged for the films with higher P content. Thus, the crystallization temperature could depend on the P content in the film. FeMnP alloy films could be used in high-frequency devices.

FRACTAL STRUCTURE OF THE CORE LOSS SPECTURM OF Fe-B-Si AMORPHOUS SOFT MAGNETIC ALLOY

The core loss spectrum P(f) of Fe-B-Si amorphous soft magnetic alloy has been studied.It is found that P(f) has the fractal structure.The effect of heat treatment on the fractal dimension Df is discussed.

Performance improvement of Fe-6.5Si soft magnetic composites with hybrid phosphate-silica insulation coatings

Fe-6.5Si soft magnetic composites(SMCs)with hybrid phosphate-silica insulation coatings have been designed to improve their comprehensive property via chemical coating combining sol-gel method in this work.The microstructure and magnetic performance of the Fe-6.5Si SMCs with hybrid phosphate-silica insulation coatings were investigated.The hybrid phosphate-silica coatings with high heat resistance and high withstand pressure,formed on the surface of the Fe-6.5Si ferromagnetic powders,were found stable in the composites.Compared with Fe-6.5Si SMCs coated by single phosphate or single silica,Fe-6.5Si SMCs with hybrid phosphate-silica show much higher permeability and lower core loss.The work provides a new way to optimize the magnetic performance of soft magnetic composites.

Preparation and characterization of carbonyl iron soft magnetic composites with magnesioferrite insulating coating layer

Spherical carbonyl iron(Fe)powders were coated with magnesioferrite(MgFe2O4)insulating coating layer and then mixed with epoxy-modified silicone resin(ESR).Soft magnetic composites(SMCs)were fabricated by compaction of the coated powders and annealing treatment.Transmission electron microscopy(TEM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray diffractometry(XRD)and X-ray photoelectron spectroscopy(XPS)revealed that the MgFe2O4 layer was coated on the surface of the iron powders.The magnetic properties of SMCs were determined using a vibrating sample magnetometer and an auto testing system for magnetic materials.The results showed that the SMCs prepared at 800 MPa and 550℃ exhibited a significant core loss of 167.5 W/kg at 100 kHz and 50 mT.

Powder injection molding of Fe-Ni soft magnetic alloys

With miniaturization and complication of the shape of electronic devices in recent years,powder injection molding(PIM)seems to be a suitable process for fabricating the higher performance soft magnetic components.In this paper,high quality Fe-50Ni soft magnetic alloy was fabricated by PIM with carbonyl iron and nickel,and the effect of sintering process on its microstructure and magnetic properties were investigated.The mechanical and magnetic properties can be obviously improved by increasing the sintering temperature or using the hydrogen atmosphere instead of high vacuum,which causes by the increase of grain size and the densification.At the optimum sintering conditions,the PIM Fe-50Ni soft magnetic alloy with high properties are obtained,whose relative density,tensile strength,B_(m),H_(c),μ_(m)are 97%,465 MPa,1.52 T,16.62 A·m^(-1),42.5 mH·m^(-1),respectively.

Influence of electroplating conditions on magnetic properties of Fe-36wt.% Ni alloy film

A Fe-Ni soft magnetic film was prepared in sulphate solution by electroplating.The influences of the molar ratio of n[Fe^(2+)]/n[Ni^(2+)],current density,bath temperature,pH and L-ascorbic acid concentration on magnetic properties of Fe-Ni alloy film were investigated.The results show that the saturated flux density(BS)of the film increases initially and decreases after it reaches the specific value with the increase of n[Fe^(2+)]/n[Ni^(2+)]molar ratio,current density,bath temperature and pH.However,the relationship between L-ascorbic acid concentration and BS keeps linear.It is observed that the coercive force(H_(c))is enhanced with the increase of n[Fe^(2+)]/n[Ni^(2+)]molar ratio,current density and pH.By comparison,when the bath temperature increases,Hc always decreases.With the increase of L-ascorbic acid concentration,the coercive force increases initially and then decreases.

Effect of niobium on glass-formation ability and soft magnetic properties of Gd-doping glassy alloys

The effect of niobium on glass-formation ability and soft magnetic properties were studied in Fe-Gd-B glassy alloys. The glassy alloys exhibited high glass-formation ability when the element of Nb was added. Bulk glassy rod （Fe0.87Co0.13）68.5Gd3.5Nb3B25 with a diameter up to 3 mm was produced by copper mold casting. The size of the atom might play an important role in increasing glass-formation ability. The coercive force of glassy （Fe0.87Co0.13）71.5.xGd3.sNbxB25 （x=1.2, 1.5, 2, 2.5, 3, 4） alloys decreased after the addition of niobium element and was in the range of 1.5-2.9 A/m. The permeability spectrum of （Fe0.87Co0.13）70.3Gd3.5Nb1.5B25 glassy ribbon showed that the relaxation frequency （f0） was 6.1 MHz.

Manufacture of Bulk Amorphous Crystal and Micro-Crystal for Pr_(60)Cu_((20-x))Ni_(10)Al_(10)Fe_x and Characteristics of Its Magnetic Apparatus

Bulk amorphous crystal and microcrystal for Pr60Cu(20-x)Ni10Al10Fex (x = 0, 8, 15, 20) with the diameter ofΦ2 ~ 6 mm were manufactured by electric arc smelting, high frequency heating and copper mold upper suction casting, and its structure was analyzed by X-ray diffract meter. It showed soft magnetic characteristic gradually when Fe content in it was up to 8% . The material was applied to magnetic-electric sensor as key component, output signal of which was measured with the change of Fe content. It shows that the signal changes from weak to strong with the increase of Fe content and presents the largest peak value when Fe is replaced by Cu completely.

Reduction of Coercivity of Fe-N Soft Magnetic Film by Heat Treatment

200 nm thick Fe-N magnetic thin films were deposited on glass substrates by RF sputtering. The as-deposited films have high saturation magnetization but their coercivity is also higher than what is needed Therefore it is very important to reduce coercivity. The samples were vacuum annealed at 250℃ under 12000 A/m magnetic field. When the N content was in the range of 5-7 at. pct, the thin films consisted of α' +α' after heat treatment and had excellent soft magnetic properties of 4πMs=2.4 T, HC <80 A/m. However, the thickness of a recording head was 2μm, and Hc increased as thickness increased. In order to reduce the Hc, the sputtering power was raised from 200 W to 1000 W to reduce the grain size. 2μm Fe-N thin films were vacuum annealed under the same condition, when the N content was in the range of 5.9-8.5 at. pct, the thin films kept its excellent magnetic properties of 4πMs=2.2 T, HC <80 A/m. The properties of the films meet the need of a recording head material used in the dual-element GMR/inductive heads.

Serrated magnetic properties in metallic glass by thermal cycle

Fe-based metallic glasses（MGs） with excellent soft magnetic properties are applicable in a wide range of electronic industry. We show that the cryogenic thermal cycle has a sensitive effect on soft magnetic properties of Fe78Si9B13 glassy ribbon. The values of magnetic induction（or magnetic flux density） B and Hc coercivity c show fluctuation with increasing number of thermal cycles. This phenomenon is explained as thermal-cycle-induced stochastically structural aging or rejuvenation which randomly fluctuates magnetic anisotropy and, consequently, the magnetic induction and coercivity. Overall,increasing the number of thermal cycles improves the soft magnetic properties of the ribbon. The results could help understand the relationship between relaxation and magnetic property, and the thermal cycle could provide an effective approach to improving performances of metallic glasses in industry.

Fabrication and magnetic properties of NiFe-ZnO nano-granular films

Excellent soft magnetic and high frequency prop- erties were obtained successfully in the （Ni75Fe25）x（ZnO）1-x granular films fabricated on the glass substrate by RF magnetron oblique sputtering. The microstructure, mag- netic and high frequency properties were investigated systematically. High resolution transmission electron micrographs show that the film consists of fcc Ni75Fe25 particles uniformly embedded in an amorphous insulating matrix ZnO with particle size a few nanometers. The （Ni75Fe25）x（ZnO）1-x films exhibit excellent soft magnetic properties in a widex range from 0.50 to 0.80 with coer- civity not exceeding 5 × 10^-4 T, which is ascribed to the exchange coupling between magnetic particles. Especially for the sample with x = 0.64, coercivities in hard and easy axes are 5.0 ×10^-5 and 3.6 × 10^-4 T, respectively, and the electric resistivity ρ reaches 1,790 μΩ.cm. The dependence of complex permeability u = u′- ju″on frequency f shows that the real part u′ is more than 130 below 500 MHz, and the ferromagnetic resonance fre- quency fr reaches 1.32 GHz, implying the promising for high frequency application.

Hopkinson Effect in Soft Magnetic Materials

The μi-T curves of the alloy Fe73.5Cu1 Nb3Si13.5B9 in the amorphous state and in the nanocrys-talline state have been investigated. For comparison, μi-T curves of the other two kinds of typical soft magnetic alloys also have been measured. It was found that a sharp Hopkinson peak appeared at the Curie point for each amorphous and crystalline alloy but there was no Hopkinson peak for the nanocrystalline alloy at the Curie point of the residual amorphous phase. This phenomenon has been explained in terms of the characteristic temperature dependence of the effective magnetic anisotropy.

High-frequency magnetic properties and core loss of carbonyl iron composites with easy plane-like structures

To fully release the potential of wide bandgap(WBG)semiconductors and achieve high energy density and efficiency,a carbonyl iron soft magnetic composite(SMC)with an easy plane-like structure is prepared.Due to this structure,the permeability of the composite increases by 3 times(from 7.5 to 21.5)at 100 MHz compared with to the spherical carbonyl iron SMC,and the permeability changes little at frequencies below 100 MHz.In addition,the natural resonance frequency of the composite shifts to higher frequencies at 1.7 GHz.The total core losses of the composites at 10,20,and 30 m T are80.0,355.3,and 810.7 m W/cm^(3),respectively,at 500 k Hz.Compared with the spherical carbonyl iron SMC,the core loss at500 k Hz is reduced by more than 60%.Therefore,this kind of soft magnetic composite with an easy plane-like structure is a good candidate for unlocking the potential of WBG semiconductors and developing the next-generation power electronics.

Behavior of Medium-frequency Core Loss in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency have been investigated in the ranges of 100 Hz<= f<=25000 Hz and 0.1 T< =Bm <=1.0 T for three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys. The measured and calculated results showed that the total power loss per cycle clearly exhibited a nonlinear behavior in the range below 3 kHz～5 kHz depending on both the magnetic state and the value of Dm, whereas it showed a quasi-linear behavior above this range. The total loss was decomposed into hysteresis loss, classical eddy current loss and excess loss, the obvious nonlinear behavior has been confirmed to be completely determined by the dependence of the excess loss on frequency. It has been indicated that the change rate of the excess loss per cycle with respect to frequency sharp decreases with increasing frequency in the range below about 3 kHz～5 kHz, wherease the rate of change slowly varies above this range, thus leading to the quasilinear behavior of the total loss per cycle. In this paper, some linear expressions of the total loss per cycle has been given in a wider medium-frequency segment, which can be used for roughly estimating the total loss.