Soft magnetic properties and giant magneto-impedance effect of Fe73.5−xCrxSi13.5B9Nb3Au1 (x=1–5) alloys

In this paper, the effect of microstructural and surface morphological developments on the soft magnetic properties and giant magneto-impedance (GMI) effect of Fe_73.5−xCr_xSi_13.5B₉Nb₃Au₁ (x=1, 2, 3, 4, 5) alloys was investigated. It was found that the Cr addition causes slight decrease in the mean grain size of α-Fe(Si) grains. AFM results indicated a large variation of surface morphology of density and size of protrusions along the ribbon plane due to structural changes caused by thermal treatments with increasing Cr content. Ultrasoft magnetic properties such as the increase of magnetic permeability and the decrease of coercivity were observed in the samples annealed at 540 °C for 30 min. Accordingly, the GMI effect was also observed in the annealed samples.     

Role of Niobium in the nanocrystallization of a Fe73.5Si13.5B9Nb3Cu alloy

The nanostructure of a nanocrystalline Fe_73.5Si_13.5B₉Nb₃Cu alloy has been studied by means of Mössbauer spectroscopy, 1D and 3D atom probes. After 6 h at 520 °C, the crystallized fraction of the alloy is about 53%. α$\mathrm{\alpha }$-Fe(Si) nanocrystals, 10–20 nm in diameter, are embedded in a retained amorphous matrix. They have a near Fe₈₀Si₂₀ composition and exhibit a DO₃ structure. The very low number density of Cu-rich particles does not match with the hypothesis of a systematic heterogeneous precipitation of α$\mathrm{\alpha }$-Fe close to Cu-rich particles. A detailed analysis of the distribution of alloying elements in the retained amorphous matrix reveals the formation of a Nb-rich shell around α$\mathrm{\alpha }$-Fe(Si) nanocrystals. It is proposed that this shell is formed during the growth of nanocrystals and the decomposition of the matrix, which tends toward a Fe₃B composition. The Nb-rich shell behaves as a diffusion barrier which inhibits the growth of nanocrystals. However, despite the presence of a Nb-rich shell, the junction between adjacent nanocrystals may occur, even if this phenomenon is rare.     

The existence of giant magnetocaloric effect and laminar structure in Fe73.5−xCrxSi13.5B9Nb3Cu1

Amorphous soft magnetic ribbons Fe_73.5−xCr_xSi_13.5B₉Nb₃Cu₁ (x=1–5) have been fabricated by rapid quenching on a single copper wheel. The differential scanning calorimetry (DSC) patterns showed that the crystallization temperature of α-Fe(Si) phase is ranging from 542 to 569 °C, a little higher than that of pure Finemet (x=0). With the same annealing regime, the crystallization volume fraction as well as the particle size of α-Fe(Si) crystallites decreased with increasing Cr amount substituted for Fe in studied samples. Especially, the interesting fact is that the laminar structure of heat-treated ribbons on the surface contacted to copper wheel in the fabricating process has been firstly discovered and explained to be related to the existence of Cr in studied samples. The hysteresis loop measurement indicated that there is the pinning of displacement of domain walls. The giant magnetocaloric effect (GMCE) has been found in amorphous state of the samples. After annealing, the soft magnetic properties of investigated nanocomposite materials are desirably improved.     

Annealing effect on soft magnetic properties and magnetoimpedance of Finemet Fe73.5Si13.5B9Nb3Au1 alloy

Effect of annealing on the soft magnetic properties of Fe_73.5Si_13.5B₉Nb₃Au₁ amorphous ribbon has been investigated by means of structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range of 1–10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 °C for 30, 60, 90 min, soft magnetic properties have been improved drastically. Among the samples investigated, the sample annealed at 530 °C for 90 min showed the softest magnetic behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing.     

Structural and magnetic properties of Co1−xZnxFe2O4 nanoparticles by co-precipitation method

Co_1−xZn_xFe₂O₄ nanoparticles were prepared by co-precipitation method with x varying from 0 to 1.0. The powder samples were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The average crystallite sizes of the particles were determined from XRD. X-ray analysis showed that the samples were cubic spinel. The average crystallite size (D_aveXR) of the particles precipitated was found to vary from 6.92 to 12.02 nm decreasing with the increase in zinc substitution. The lattice constant (a_o) increased with the increase in zinc substitution. The specific saturation magnetization (M_S) of the particles was measured at room temperature. The magnetic parameters such as M_S, H_c, and M_r were found to decrease with the increase in zinc substitution. FTIR spectra of the Co_1−xZn_xFe₂O₄ with x varying from 0 to 1.0 in the range 400–4000 cm⁻¹ were reported. The spinel structure and the crystalline water adsorption of Co_1−xZn_xFe₂O₄ nanoparticles were studied by using FTIR.     

Magnetic properties of nanocrystalline Co1−xZnxFe2O4 prepared by forced hydrolysis method

Nanocrystalline zinc-substituted cobalt ferrite powders, Co_1−xZn_xFe₂O₄ (x=0, 0.2, 0.4), were for the first time prepared by forced hydrolysis method. Magnetic and structural properties in these specimens were investigated. The average crystallite size is about 3.0 nm. When the zinc substitution increases from x=0 to x=0.4, at 4.2 K, the saturation magnetization increases from 72.1 to 99.7 emu/g and the coercive field decreases from 1.22 to 0.71 T. All samples are superparamagnetic at room temperature and ferrimagnetic at temperatures below the blocking temperature. The high value of the saturation magnetization and the very thin thickness of the disorder surface layer of all samples suggests that this forced hydrolysis method is suitable not only for preparing two metal element systems but also for three or more ones.     

Magnetic viscosity-coercivity relation for Fe1−xCox fine particles

The variation of the applied field results in a subsequent change of magnetization with time. There is a relationship between the coercivity (H_c), as the equilibrium characteristic of the system, and its magnetic stability (1/S), as a parameter characterizing the time dependence. 1/S as a function of H_c has been measured and studied for different Fe_1−xCo_x samples. We synthesized several samples with different values of x by applying various magnetic fields during the grains’ growth, and observed a linear relationship between 1/S and H_c.     

Monodispersed nanocrystalline Co1–xZnxFe2O4 particles by forced hydrolysis: Synthesis and characterization

Zinc-substituted cobalt ferrites, Co_1–xZn_xFe₂O₄, were for the first time successfully prepared by forced hydrolysis method. The obtained materials are single phase, monodispersed nanocrystalline with an average grain size of about 3 nm. These materials are superparamagnetic at room temperature and ferrimagnetic at temperature lower than the blocking temperature. When the zinc substitution increases from x=0 to 0.4, at 4.2 K, the saturation magnetization increases from 72.1 to 99.7 emu/g. The high saturation magnetization of these samples suggests that this method is suitable for preparing high-quality nanocrystalline magnetic ferrites for practical applications.     

Effect of carbon content on structure and magnetic properties for (Fe,Ni)1−xCx by mechanical alloying

FCC (Fe₅₅Ni₄₅)_1−xC_x   supersaturated solid solution was prepared in a wide concentration range (0?x?0.9)$(0?x?0.9)$ by mechanical alloying of nanocrystalline Fe₅₅Ni₄₅ with graphite. The lattice constant of Fe₅₅Ni₄₅ increases linearly with increasing carbon content up to x=0.25$x=0.25$. At the same time, it is found that the magnetic moment per metal atom (Fe, Ni) decreases linearly with increasing carbon content for 0?x?0.25$0?x?0.25$ with a slope of 1.2 μ_B/at. For high carbon content, x?0.5$x?0.5$, it is observed that the decrease of lattice constant and increase of moment per metal atom (Fe, Ni) with increasing C content, indicates that the dissolution of carbon is hindered by the high-volume fraction of graphite in the initial powder mixture. The complete amorphization of x=0.5$x=0.5$ does not occur after the extended ball milling. The alloying effect of carbon on the magnetization is compared with other metalloid B, P, and Si in Fe- and Ni-based binary system.     

Studies of the relaxed amorphous phase in the Fe80Nb6B14 alloy

The paper presents measurements of magnetic permeability, magnetic after-effects, magnetostriction, DSC and XPS for the Fe₈₀Nb₆B₁₄ amorphous alloys preliminary annealed for 1 h at temperatures ranging from 300 to 770 K. It was shown that annealing out of free volume and internal stresses causes a decrease of magnetostriction coefficient and leads to the formation of the energetically stable relaxed amorphous state. The XPS spectra show local fluctuation of boron density. This effect was attributed to the formation of small iron clusters—the characteristic feature for the relaxed amorphous phase.     

Magnetostrictive behaviour of Fe73.5Si13.5B9Nb3−xMoxCu1 alloys

Magnetostriction, dilatation and calorimetric measurements were performed on FINEMET type as-quenched and heat treated ribbons. Nb was gradually replaced by Mo in order to study the influence of the refractory elements exchange on several magnetostriction parameters. The results could be correlated with magnetic and structural transformations throughout thermal treatments and assured that the whole series is suitable for technical applications.     

Synthesis and magnetic properties of antiferromagnetic Co3O4 nanoparticles

Antiferromagnetic Co₃O₄ nanoparticles with diameter around 30 nm have been synthesized by a solution-based method. The phase identification by the wide-angle X-ray powder diffraction indicates that the Co₃O₄ nanoparticle has a cubic spinel structure with a lattice constant of 0.80843(2) nm. The image of field emission scanning electron microscope shows that the nanoparticles are assembled together to form nanorods. The magnetic properties of Co₃O₄ fine particles have been measured by a superconducting quantum interference device magnetometer. A deviation of the Néel temperature from the bulk is observed, which can be well described by the theory of finite-size scaling. An enhanced coercivity as well as a loop shift are observed in the field-cooled hysteresis loop. The exchange bias field decreases with increasing temperature and diminishes at the Néel temperature. The training effect and the opening of the loop reveal the existence of the spin-glass-like surface spins.     

Transmission electron microscopy study of large field induced anisotropy (Co1−xFex)89Zr7B4 nanocomposite ribbons with dilute Fe-contents

Electron microscopy was employed to investigate the structure of magnetic field crystallized (Co_1−xFe_x)₈₉Zr₇B₄ alloys with only dilute Fe-contents (x=0, 0.025, 0.05, and 0.10). The x=0.025 and 0.05 alloys exhibit very large field induced anisotropies and multiple nanocrystalline phases (BCC, FCC, and HCP) surrounded by an intergranular amorphous phase. Correlation between the volume fraction crystallized and the measured value of H_K suggests that the large K_U values are associated with the crystalline phases that form. Multiple crystalline phases are present for the highest K_U alloys and so the presence of FCC and/or HCP-type nanocrystals may be responsible for these observations. High-resolution transmission electron microscopy (HRTEM) illustrates a number of microstructural features including (1) high densities of stacking faults in many of the FCC and, in particular, the HCP-type nanocrystals, (2) infrequent BCC/FCC orientation relationships, and (3) nanocrystals with disordered or long period stacking sequences of close-packed planes. High densities of planar faults are suggested as a potential source of K_U for the FCC and HCP-type nanocrystals, but the origin of the large values of K_U found in dilute Fe-containing, Co-rich “nanocomposite” alloys is an area where further work is needed.     

A study on microstructure,magnetic properties and kinetics of the nanocrystallization of Fe40Ni38B18Mo4 metglass

This study has investigated the microstructure and magnetic properties of Fe₄₀Ni₃₈B₁₈Mo₄ at various degrees of crystallization from the amorphous state. TEM and XRD studies confirmed that phases forming after crystallization at temperatures around 414 and 522 °C were cubic (Fe, Ni, Mo)₂₃B₆ phase and FCC (Fe, Ni) solid solution. The growth behavior and morphology of the nanocrystalline phases have been studied as a function of time and temperature. Nanoparticles were lying in the size range of 10–20 nm and they were stable below 522 °C. Kissinger approach, Ozawa method and Yi Qun Gao method were employed to determine and compare the kinetic parameters of the crystallization processes. A growth mechanism of crystallizing phases was proposed on the basis of these results. Magnetic properties mainly coercivity and saturation magnetization of as-received and heat-treated samples were evaluated.     

The structure and magnetic properties of Zn1−xNixFe2O4 ferrite nanoparticles prepared by sol–gel auto-combustion

Zn_1−xNi_xFe₂O₄ ferrite nanoparticles were prepared by sol–gel auto-combustion and then annealed at 700 °C for 4 h. The results of differential thermal analysis indicate that the thermal decomposition temperature is about 210 °C and Ni–Zn ferrite nanoparticles could be synthesized in the self-propagating combustion process. The microstructure and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscope, and Vibrating sample magnetometer. It is observed that all the spherical nanoparticles with an average grain size of about 35 nm are of pure spinel cubic structure. The crystal lattice constant declines gradually with increasing x from 0.8435 nm (x=0.20) to 0.8352 nm (x=1.00). Different from the composition of Zn_0.5Ni_0.5Fe₂O₄ for the bulk, the maximum M_s is found in the composition of Zn_0.3Ni_0.7Fe₂O₄ for nanoparticles. The H_c of samples is much larger than the bulk ferrites and increases with the enlarging x. The results of Zn_0.3Ni_0.7Fe₂O₄ annealed at different temperatures indicate that the maximum M_s (83.2 emu/g) appears in the sample annealed at 900 °C. The H_c of Zn_0.3Ni_0.7Fe₂O₄ firstly increases slightly as the grain size increases, and presents a maximum value of 115 Oe when the grains grow up to about 30 nm, and then declines rapidly with the grains further growing. The critical diameter (under the critical diameter, the grain is of single domain) of Zn_0.3Ni_0.7Fe₂O₄ nanoparticles is found to be about 30 nm.     

高Br纳米晶Fe73.5Cu1Nb3Si13.5B9合金的损耗行为

在f=10—20000Hz和B_m=0.1—1.0T范围内,测量了高B_r纳米晶Fe_73.5Cu₁Nb₃Si_13.5B₉合金的损耗.把总损耗分离为磁滞损耗、经典涡流损耗和过剩损耗.测量结果表明,每周损耗随频率的变化表现出明显的非线性行为.用Bertotti的损耗统计理论描述了这种非线性行为.大致在两个频率范围内,有两种不同的描述方式. 关键词：     

Magnetic domain structure in Fe78.8−xCoxCu0.6Nb2.6Si9B9 nanocrystalline alloys studied by Lorentz microscopy

The magnetic domain structures of Fe_78.8−xCo_xCu_0.6Nb_2.6Si₉B₉ (x=0, 20, 40, 60) alloys are investigated by Lorentz microscopy coupled with the focused ion beam method. The specimen prepared using the FIB method is found to have a considerably more uniform thickness compared to that prepared using the ion-milling method. In Fe_38.8Co₄₀Cu_0.6Nb_2.6Si₉B₉ and Fe_18.8Co₆₀Cu_0.6Nb_2.6Si₉B₉ alloys, 180° domain walls extending in the direction of the induced magnetic anisotropy are observed. Analysis with Lorentz microscopy reveals that the width of the magnetic domains decreases with an increase in the cobalt content or the induced magnetic anisotropy K_u, that is, the domain width d is proportional to the induced magnetic anisotropy (K_u)^−1/4. On the other hand, in the in situ Lorentz microscopy observation as a function of temperature, magnetic ripple structures are found to appear in a localized area due to the fluctuation of magnetization vectors from 423 K. It is observed that the induced magnetic anisotropy caused by the applied magnetic field at 803 K is not suppressed by the magnetic ripple structures observed at 423–443 K.     

频率对纳米晶软磁合金磁性能影响的理论解释

根据原子力显微镜（AFM）对Fe基纳米晶Fe_735Cu₁Nb_{3< /sub>Si135B9合金薄带的介观结构的研究结果，提出了解释纳米晶软磁合金磁性能的理论模型——柱、球混合模型，并成功地解释了频率对纳米晶软磁合金磁性能的影响，所得理论体现了Herzer理论和纪松理论的特点，并弥补了它们的不足，同时提出了纳米晶粒电导率σ、磁导率μ对合金磁性有影响的观点. 关键词： 铁基纳米晶合金 模型 频率 软磁性能}     

Fabrication and magnetic properties of Fe3O4 nanowire arrays in different diameters

Fe₃O₄ nanowire arrays with different diameters of D=50, 100, 150 and 200 nm were prepared in anodic aluminum oxide (AAO) templates by an electrodeposition method followed by heat-treating processes. A vibrating sample magnetometer (VSM) and a Quantum Design SQUID MPMS magnetometer were used to investigate the magnetic properties. At room temperature the nanowire arrays change from superparamagnetism to ferromagnetism as the diameter increases from 50 to 200 nm. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements show that the blocking temperature T_B increases with the diameter of nanowire. The ZFC curves of D=50 nm nanowire arrays under different applied fields (H) were measured and a power relationship between T_B and H were found. The temperature dependence of coercivity below T_B was also investigated. Mössbauer spectra and micromagnetic simulation were used to study the micro-magnetic structure of nanowire arrays and the static distribution of magnetic moments of D=200 nm nanowire arrays was investigated. The unique magnetic behaviors were interpreted by the competition of the demagnetization energy of quasi-one-dimensional nanostructures and the magnetocrystalline anisotropy energy of particles in nanowires.