Structural and magnetic properties of nanostructured Fe50(Co50)-6.5 wt% Si powder prepared by high energy ball milling

This work investigates the effects of 6.5 wt% Si addition and milling times on the structural and magnetic properties of Fe₅₀Co₅₀ powders. For this purpose, at first the elemental Fe and Co powders were milled for 10 h to produce Fe₅₀Co₅₀ alloy and then Si was added and the new product was milled again for different times. The microstructural and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results show that the minimum crystallite size of the as-milled powders (∼12 nm) has been achieved after introducing Si and milled for 8 h (total milling time of 18 h). Also an amount of 188 emu/g has been achieved for M_s. This amount of M_s is higher than most of those which have been already reported for M_s of different Fe-Si systems.     

FMR study of thin films of Co2Cr0.6Fe0.4Al and Co2MnSi Heusler alloys

The method of ferromagnetic resonance (FMR) was used to study magnetic properties of thin films of half-metallic ferromagnetic Heusler alloys Co₂Cr_0.6Fe_0.4Al and Co₂MnSi depending on the film thickness and the presence or absence of a vanadium buffer layer. It is shown that the FMR method is a highly efficient technique for studying nanoscale magnetic properties of thin films, especially for the investigation of their magnetic inhomogeneities and anisotropy. Samples of Co₂Cr_0.6Fe_0.4Al and Co₂MnSi were prepared by magnetron-sputtering deposition on substrates of single-crystal silicon dioxide (SiO₂) with an orientation (100). It has been shown that the magnetic properties of thin Co₂Cr_0.6Fe_0.4Al films strongly depend on both the film thickness (25 or 100 nm) and the presence of an intermediate vanadium layer (50 nm). Well-resolved spin-wave modes were observed in the sample 100 nm thick without a vanadium buffer layer, which made it possible to determine the parameter of spin stiffness D for this ferromagnet. Two series of thin films of Co₂MnSi have also been studied, which were prepared on a buffer layer of vanadium (42 nm thick): (1) with various thicknesses (4–100 nm) and a fixed annealing temperature (450°C) and (2) with a fixed thickness (80 nm) and various annealing temperatures (425–550°C). It has been shown that in the series of Co₂MnSi films with a variable thickness (4–100 nm) the greatest value of magnetization is reached for a film with a thickness of 61 nm. The investigations of the other series of films, which were annealed at various temperatures, show that to achieve both a greater magnetization and a better structural homogeneity, annealing at temperatures T ≥ 450°C is required. In addition, low-intensity spin-waves were observed in some samples with thicknesses of 100 and 61 nm, which made it possible to estimate the spin-stiffness parameter D for the Co₂MnSi Heusler alloy as well.     

Magnetic and structural studies of mechanically alloyed (Fe50Co50)62Nb8B30 powder mixtures

Amorphous (Fe₅₀Co₅₀)₆₂Nb₈B₃₀ powder mixture was prepared by mechanical alloying from elemental Fe, Co, B and Nb powders in a planetary ball mill under argon atmosphere. Structural, thermal and magnetic properties were performed on the milled powders by means of X-ray diffraction, differential scanning calorimetry and magnetic measurements. The amorphous state is reached after 125 h of milling. The excess enthalpy due to the high density of defects is released at temperature below 300 °C. Crystallisation and growth of crystal domains are the dominating processes at high temperatures. The saturation magnetisation decreases rapidly during the first 25 h of milling to about 15.24 A m²/kg and remains nearly constant on further milling. Coercivity, H_c, value of about 160 Oe is obtained after 125 h of milling.     

Improvement of soft magnetic properties of CoFeSiB thin film by external magnetic field and Zr addition

Co₄₀Fe₁₇Si₃₂B₁₁ thin film (150 nm) was deposited by using an RF magnetron co-sputtering system on a Si (100) substrate. A self-designed substrate holder, including various hard magnets arranged around the substrates, was utilized so that various external magnetic fields could be applied to the Si substrates during the film deposition. By the effect of this deposition field, the applied field during the sample deposition, the squareness of the CoFeSiB thin film was significantly enhanced. From the angular analysis of the magnetic hysteresis curves from easy (parallel to external magnetic field) to hard (perpendicular to external magnetic field) direction of magnetization, it can be deduced that Co and Fe atoms were magnetically arranged to the easy magnetization axis by an external magnetic field which was induced during deposition. Also, the compositional cluster size of the CoFeSiB thin film was remarkably reduced by Zr addition, causing a decrease in the value of coercivity. These results suggest that apparent magnetic anisotropy was achieved, and the soft magnetic property of the CoFeSiB thin film was remarkably enhanced by the combination of the deposition field and Zr addition.     

Laser ablated Fe100−xPdx and Fe100−xMnx thin films (x=20 and 50)

Thin films (50 nm) of Fe_100−xPd_x and Fe_100−xMn_x (x=20 and 50) were deposited by laser ablation on a Si wafer and studied by X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). In all cases, the XRD patterns of the target surface before and after ablation show a congruent transfer of ablated material. For the Fe₈₀Pd₂₀ thin film, XRD spectra show the formation of FePd, iron, Pd oxide and traces of hematite in the ablated film. Complementary information obtained by CEMS indicates the presence of an upper 50-nm thick surface layer of hematite in the deposited film. Fe₅₀Pd₅₀ phase was observed by CEMS and a Pd oxide component was identified by XRD, along with traces of hematite. In the case of Fe₈₀Mn₂₀, the CEMS spectrum is consistent with the occurrence of the antiferromagnetic FeMn phase and the XRD pattern also shows the presence of Fe in the structure. For the system Fe₅₀Mn₅₀, we obtain by CEMS an antiferromagnetic phase of FeMn and by XRD we trace the presence of nanohematite and in-depth iron. For x=20 in both iron-rich systems investigated, we observe the segregation of iron with subsequent conversion to hematite. The study shows that the stoichiometry of the compounds plays a decisive role in determining their structural and magnetic properties.     

Annealing effect on the soft magnetic properties of high moment FeCo–O thin films

We have investigated the annealing effect on the soft magnetic properties of high magnetic moment (Fe_0.65Co_0.35)_100−xO_x (0<x<5 at.%) thin films. The coercivity of the as-deposited (Fe_0.65Co_0.35)₉₉O₁ film decreased from 120 to 5 Oe after annealing at 480 °C. The reason for this vast magnetic softening is discussed based on the microstructural observation results.     

Magnetoresistive sensitivity and uniaxial anisotropy of spin-valve microstrips with a synthetic antiferromagnet

Microobjects (strips) were formed by contact photolithography using Та/Ni₈₀Fe₂₀/Co₉₀Fe₁₀/Cu/Co₉₀Fe₁₀/Ru/Co₉₀Fe₁₀/Fe₅₀Mn₅₀/Ta spin-valves prepared by magnetron sputtering. A mutually perpendicular arrangement of uniaxial and unidirectional anisotropy axes in microobjects has been formed using two different thermomagnetic treatment regimes. The magnetoresistive sensitivity of spin valve and spin-valve-based microobject has been found to depend on the mutual arrangement of the easy magnetization axis and direction of magnetic field applied upon thermomagnetic treatment. The obtained data have been interpreted taking into account changes in the induced anisotropy and anisotropy due to the shape of the microobject.     

Thermoelectric properties of tin-filled skutterudites prepared by mechanical alloying process

Sn-filled (Fe, Co)Sb₃ skutterudites of the form of Sn_yFe₃Co₅Sb₂₄ (0≤y≤1.5) were synthesized by the mechanical alloying of elemental powders followed by vacuum hot pressing. The phase transformations that occur during both mechanical alloying and vacuum hot pressing were examined by X-ray diffraction. Single-phase Sn-filled skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. The thermoelectric properties of the hot-pressed specimens were evaluated as a function of temperature and tin content. The void filling of tin (up to y=1.0) in Fe₃Co₅Sb₂₄ appeared to increase the thermoelectric figure of merit.     

Induced magnetic anisotropy in permalloy films annealed with magnetic field

The effect of magnetic annealing on Fe₂₁Ni₇₉ films was investigated through the characterization of crystal structure and magnetic properties. Fe₂₁Ni₇₉ films were deposited on thermally oxidized Si substrates using a DC magnetron sputter. A highly a-axis oriented Fe₂₁Ni₇₉ film was grown on Si substrate by magnetic annealing. Columnar grain growth was dominant in the films annealed with magnetic field. Both the area surrounded by hysteresis curve, and coercivity, were increased by magnetic annealing, indicating that the magnetic annealing induced the anisotropy energy. Through EXAFS analysis, 1.19×10^?3 was obtained as the strain of a specimen annealed with magnetic field. This value confirmed that induced magnetic anisotropy was formed by atomic pair ordering.     

Structure and magnetic, electrical, and optical properties of thin films of Fe2NbSn and Co2Cr0.6Fe0.4Al Heusler alloys prepared by the method of magnetron sputtering

Method of magnetron sputtering of mosaic targets has been used to prepare thin films of Fe₂NbSn and Co₂Cr_0.6Fe_0.4Al Heusler alloys. In these alloys, the band calculations predict the existence of a high degree of polarization of charge carriers. The chemical composition and the magnetic and structural characteristics of the films of both compounds have been studied. In the films of the Fe₂NbSn alloy, which never has been investigated previously, we also studied optical and electrical properties. Based on the data obtained, we concluded that we obtained films with a composition close to stoichiometric. The annealing of the films leads to the appearance of a crystal structure and magnetic properties that correspond to the theoretical calculations. In the case of the Co₂Cr_0.6Fe_0.4Al alloys, the structural and magnetic characteristics are identical to the literature data for the films obtained using continuous targets.     

Effect of phase separation in an Fe20Ni80/Fe50Mn50 structure with exchange coupling

The effect of heat treatment and partial oxidation of an Fe₅₀Mn₅₀ layer on the structure and magnetic properties of exchange-coupled Fe₂₀Ni₈₀/Fe₅₀Mn₅₀ layers has been investigated. The behavior of the exchange-bias field and coercive force depending on the temperature of annealing upon heat treatment in a vacuum or in an oxygen-containing gas mixture has been studied. It has been shown that, by adjusting the parameters of annealing in the gas mixture, it is possible to increase the field of switching of the exchange-coupled Fe₂₀Ni₈₀/Fe₅₀Mn₅₀ layers.     

Formation and magnetic properties of nanocrystalline Fe60Co40 alloys produced by mechanical alloying

The Fe₆₀Co₄₀ alloys were prepared by mechanical alloying of the Fe and Co powders using a high-energy ball mill. They were studied with respect to phase formation and magnetic properties using x-ray diffraction, scanning electron microscopy, and measurements of coercivity and remanence (B _r). The evaluation of Fe lattice parameters during milling showed that formation of a body-centered cubic solid solution occurred by mechanical alloying after 12 h of milling. Intensive milling of Fe-Co powders results in a nonequilibrium microstructure characterized by grain refinement to a minimum of 10–13 nm and the introduction of internal strain up to 0.5%.     

Hydrothermal growth and characterization of magnetite (Fe3O4) thin films

Well-crystallized magnetite (Fe₃O₄) thin films were successfully prepared by a simple hydrothermal process using hydrazine hydrate as the mineralizer. X-ray diffraction and scanning electron microscopy (SEM) and transmission electron microscopy were employed to characterize the products. SEM images show that the uniform Fe₃O₄ film (∼ 3 μm in thickness) is firmly grown on a nickel substrate. The magnetic property of the Fe₃O₄ particles scraped from the film was measured by Physical Property Measurement System (PPMS) at room temperature, and the magnetization curve reveals a soft ferromagnetic behavior with high saturation magnetization of 85 emu/g. Furthermore, the chemical and growth mechanisms for the hydrothermal formation of the Fe₃O₄ film are discussed.     

Structure and magnetic properties of mechanically alloyed Tb0.2Pr0.8（Fe0.4Co0.6）1.93 and magnetostriction of its epoxy composite

The C15 Laves phase with composition Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 was synthesized by mechanical alloying (MA) and subsequent annealing process. The structure and magnetic properties of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 were investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer, and a standard strain technique. The effect of annealing on the structure and magnetic properties was studied. The analysis of XRD shows that the high Pr-content Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 alloy with the single phase of MgCu₂-type structure can be successfully synthesized by MA method. The sample annealed at 450°C is found to have a coercivity of 196 kA/m at room temperature. An epoxy/Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 composite was produced by a cold isostatic pressing technique. A large magnetostriction of 400 ppm, at an applied magnetic field of 800 kA/m, was found for the composite. The epoxy-bonded Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 composite combines a high magnetostriction with a significant coercivity, which is a promising magnetostrictive material.     

Milling and subsequent thermal annealing effects on the microstructural and magnetic properties of nanostructured Fe90Co10 and Fe65Co35 powders

The influence of milling and subsequent annealing on the microstructural and magnetic properties of Fe₉₀Co₁₀ and Fe₆₅Co₃₅ alloys is investigated. After milling for 8 h a body-centred cubic nanostructured Fe–Co alloy forms with an average crystallite size of about 12 nm. The magnetization saturation (M_S) increases 16% for Fe₆₅Co₃₅ and 5% for Fe₉₀Co₁₀ alloys by milling for 8 h. Subsequent annealing of Fe₉₀Co₁₀ and Fe₆₅Co₃₅ powders for 105 min at 550 °C improves the M_S about 6 and 11%, respectively. Before annealing, the coercivity increases (up to 60 Oe) by milling for 3 h, followed by a reduction on milling for longer periods (45 h). At the initial stage of the heating, a sharp decrease in H_C to 8–10 Oe occurs due to the relief of internal strain. Further heating leads to an increase in the coercivity (intermediate times) followed by a slight diminution on heating for final stage.     

Effect of Structure on the Magnetic Properties of Rapidly Hardened Powders of the Nd – Fe – B System

The structure and magnetic properties of rapidly hardened powders from alloys based on Nd₂Fe₁₄B compounds are studied. Centrifugally sprayed powders with a multiphase structure bearing Nd₂Fe₁₄B, Nd(OH)₃, and α-Fe phases are described. A decrease in the size of crystals of the magnetic phases (Nd₂Fe₁₄B and α-Fe) and the amount of α-Fe are shown to increase the magnetic properties of such powders. At the same time, powders obtained by melt spinning are shown to be single-phase ones with more dispersed crystals and higher magnetic properties.     

MAGNETOMECHANICAL DAMPING CAPACITY OF <110> ORIENTED Tb0.36Dy0.64(Fe0.85Co0.15)2 ALLOY

采用区熔定向凝固方法, 以480 mm/h速度制备了<110>取向Tb_0.36Dy_0.64(Fe_0.85Co_0.15)₂合金棒. 通过测试在0---0.325 T磁场范围内合金 棒的应力--应变回线, 计算了应力幅σ_m分别为-10,-30和-50 MPa的阻尼系数Δ W/W. 结果表明, 零磁场下的Δ W/W最大; 随磁场强度增大, 同一σ_m条件下的Δ W/W逐渐降低. 在低磁场中, Δ W/W随σ_m的增加而降低; 在高磁场中,  Δ W/W随σ_m的增加而升高. 利用不同预压应力下的磁致伸缩--磁化强度关系曲线, 分析了磁场--应力复合加载条件下非180°磁畴和畴壁的运动形式. 依据局部内应力理论, 解释了合金棒的磁机械阻尼系数随外磁场强度和应力幅值变化的规律.     

Influences of NiCO<Subscript>3</Subscript> content on the microstructure and magnetic properties of Ni<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> powders prepared by SHS

Stoichiometric Ni_0.5Zn_0.5Fe₂O₄ powders were produced by self-propagating high temperature synthesis (SHS). The effects of NiCO₃ content in the raw materials on the microstructure and magnetic properties of Ni-Zn ferrite powders were systematically studied. The Ni_0.5Zn_0.5Fe₂O₄ powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The magnetic properties of the powders were evaluated by vibrating sample magnetometry (VSM). The results show that the introduction of NiCO₃ into reactants improves the conversion percentage and refines the Ni_0.5Zn_0.5Fe₂O₄ particles. The increase of NiCO₃ content enhances the magnetic properties of Ni_0.5Zn_0.5Fe₂O₄. Particularly, the saturation magnetization reaches the maximum when the NiCO₃ content is 3 at.%.     

Air-oxidation behavior of a [(Fe50Co50)75B20Si5]96Nb4 bulk metallic glass at 500–650 °C

The oxidation behavior of a [(Fe₅₀Co₅₀)₇₅B₂₀Si₅]₉₆Nb₄ bulk metallic glass was studied over the temperature range of 500–650 °C in dry air. The oxidation kinetics generally followed the parabolic-rate law, and the parabolic-rate constants (k_p values) of the glassy alloy increased with increasing temperature. The k_p values of the glassy alloy were lower than those of the binary FeCo alloy. The scales formed on the FeCo alloy consisted of Fe₃O₄ and minor Fe₂O₃, while B₂O₃ was also observed on the amorphous substrate, whose formation may be responsible for the slower oxidation rates of the glassy alloy.     

Microstructures and magnetic properties of carbon nanotube/Co-oxide nanocomposite powders

Carbon nanotube embedded cobalt oxide (CNT/Co-oxide) nanocomposite powders were synthesized by molecular-level mixing followed by calcination. The surface morphology of the fabricated nanocomposite powders shows Co-oxide coated CNTs homogeneously dispersed in the Co-oxide nanopowders. XRD patterns reveal that CoO–Co₃O₄ nanopowders were obtained as a complex phase. The nanocomposite powders exhibit ferromagnetism with a saturation magnetization of 75emu g^?1, while CoO–Co₃O₄ nanopowders without CNTs are paramagnetic. These results indicate that incorporating CNTs into Co-oxide nanopowders triggers a change of the magnetic properties towards ferromagnetism.