Recoilless fraction, structural, magnetic and thermal properties of Fe73.5Cu1Nb3Si13.5B9 alloy

Differential scanning calorimetry, X-ray diffraction and room temperature Mössbauer spectrum measurements of Fe_73.5Cu₁Nb₃Si_13.5B₉ (Finemet) alloy have been carried out in order to study its structural and magnetic properties as a function of annealing temperature. The DSC profile of as-quenched Finemet showed two exothermic peaks at 530 and 702 °C, corresponding to two crystallization processes. The Finemet alloy remains amorphous at 450 °C with one broad peak in XRD pattern and one broad sextet in Mössbauer spectrum. When the Finemet alloy was annealed at 550 °C, only well indexed body-center-cubic phase was detected. After being annealed at 650 and 750 °C, the XRD patterns showed the coexistence of α-Fe(Si) and Fe-B intermetallic phases with the increase in XRD peak intensities, indicating the growth of crystallites and the decomposition of Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy at elevated temperatures. The Mössbauer spectra of annealed Finemet alloy could be fitted with 4 or 5 sextets and one doublet at higher annealing temperatures, revealing the appearance of different crystalline phases corresponding to the different Fe sites above the crystallization temperature. The appearance of the nanocrystalline phases at different annealing temperatures was further confirmed by the recoilless fraction measurements.     

Microstructure evolution in the rapidly quenched Fe78Si9B13 ribbons

We report microstructure evolution in as-spun Fe₇₈Si₉B₁₃ ribbons under various wheel speeds (s), which was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). With decreasing s, the volume fraction of the residual amorphous phase (V_a) in the as-spun ribbons decreases gradually, and the total exothermic heat of the crystallization in the DSC curves also decreases, but the ratio of the exothermic heat of the second crystallization to the first one is on the contrary. α-Fe is found in the ribbon with s of 32.9 m/s, while α-Fe, eutectic α-Fe+Fe₂B, and Fe₃Si phases are found in ribbons with s of 25.6 and 18.3 m/s. The phase precipitating behavior in cooling processes is well consistent with the annealing process in the literatures.     

Effect of the heat treatment on the corrosion behaviour of amorphous Fe-Cr-P-C-Si alloy in 0.5 M H2SO4

The effect of the heat treatment on the corrosion behaviour of amorphous Fe₈₅Cr₅P₆C₃Si alloy in 0.5 M H₂SO₄ has been investigated using electrochemical techniques. Heat treatment was carried out at temperatures varying between 250 and 650 °C at different times 30, 60, 120 and 240 min. The evolution of crystallization processes after annealing was identified by differential thermal analysis (DTA) and by X-ray diffraction (XRD). The diagrams obtained by DTA show that the structure of samples treated at high temperature changes towards a crystalline state. This crystallization phenomenon is confirmed by the analysis with the XRD. The results obtained from the polarization curves reveal that for all the studied temperatures of annealing, Fe-Cr-P-C-Si exhibits a phenomenon of passivation without breakdown of passivity. The best corrosion resistance is obtained at the temperature of annealing 350 °C. For an annealing at higher temperatures, Fe₈₅Cr₅P₆C₃Si becomes less corrosion resistant than same amorphous alloy treated with temperatures lower than 350 °C.     

Mössbauer spectroscopy studies of spin reorientations in amorphous and crystalline (Co0.2Fe0.8)72.5Si12.5B15 glass coated micro-wires

Thermo-gravimetric, differential scanning calorimetry and comprehensive ⁵⁷Fe Mössbauer spectroscopy studies of amorphous and crystalline ferromagnetic glass coated (Co_0.2Fe_0.8)_72.5Si_12.5B₁₅ micro-wires have been recorded. The Curie temperature of the amorphous phase is T_C(amorp) ∼730 K. The analysis of the Mössbauer spectra reveals that below 623 K the easy axis of the magnetization is axial-along the wires, and that a tangential or/and radial orientation occurs at higher temperatures. At 770 K, in the first 4 hours the Mössbauer spectrum exhibits a pure paramagnetic doublet. Crystallization and decomposition to predominantly α-Fe(Si) and Fe₂B occurs either by raising the temperature above 835 K or isothermally in time at lower temperatures. Annealing for a day at 770 K, leads to crystallization. In the crystalline material the magnetic moments have a complete random orientation. After cooling back to ambient temperature, both α-Fe(Si) and Fe₂B in the glass coated wire show pure axial magnetic orientation like in the original amorphous state. The observed spin reorientations are associated with changes in the stress induced by the glass coating.     

Crystallization behavior and microstructure of Fe75Co6Zr9B10 alloy

Fe₇₅Co₆Zr₉B₁₀ amorphous alloy prepared by melt-spinning was annealed at various temperatures. The crystallization behavior and microstructure were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The three exothermal peaks in the DTA curve of Fe₇₅Co₆Zr₉B₁₀ amorphous alloy correspond to the formations of α-Fe and α-Mn type phases, the growth of BCC-Fe volume fraction at the expense of α-Mn and residual amorphous phase and the precipitations of Fe₃Zr, etc. intermetallic compounds, respectively. The second exothermic peak is not influenced by heating rate, but it shifts to a higher temperature region with increasing preannealing temperature of Fe₇₅Co₆Zr₉B₁₀ alloy. The α-Mn type phase is metastable and its lattice parameter determined by TEM is 0.8830 nm. AFM images show the development of surface morphology of alloy after annealing. The particle size increases with increasing annealing temperature.     

The effect of different temperature annealing on phase relation of LaFe11.5Si1.5 and the magnetocaloric effects of La0.8Ce0.2Fe11.5−xCoxSi1.5 alloys

The phase relation of LaFe_11.5Si_1.5 alloys annealed at different high-temperature from 1223 K (5 h) to 1673 K (0.5 h) has been studied. The powder X-ray diffraction (XRD) patterns show that large amount of 1:13 phase begins to form in the matrix alloy consisting of α-Fe and LaFeSi phases when the annealing temperature is 1423 K. In the temperature range from 1423  to 1523 K, α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase, and LaFeSi phase is rarely observed in the XRD pattern of LaFe_11.5Si_1.5 alloy annealed at 1523 K. With annealing temperature increasing from 1573  to 1673 K, the LaFeSi phase is detected again in the LaFe_11.5Si_1.5 alloy, and there is La₅Si₃ phase when the annealing temperature reaches 1673 K. There almost is no change in the XRD patterns of LaFe_11.5Si_1.5 alloys annealed at 1523 K for 3-5 h. According to this result, the La_0.8Ce_0.2Fe_11.5−xCo_xSi_1.5 (0≤×≤0.7) alloys are annealed at 1523 K (3 h). The analysis of XRD patterns shows that La_0.8Ce_0.2Fe_11.5xCo_xSi_1.5 alloys consist of the NaZn₁₃-type main phase and α-Fe impurity phase. With the increase of Co content from x=0 to 0.7, the Curie temperature T_C increases from 180 to 266 K. Because the increase of Co content can weaken the itinerant electron metamagnetic transition, the order of the magnetic transition at T_C changes from first to second-order between x=0.3 and 0.5. Although the magnetic entropy change decreases from 34.9 to 6.8 J/kg K with increasing Co concentration at a low magnetic field of 0-2 T, the thermal and magnetic hysteresis loss reduces remarkably, which is very important for the magnetic refrigerant near room temperature.     

Preparation,microstructure, and magnetic properties of a nanocrystalline Nd12Fe82B6 alloy by HDDR combined with mechanical milling

Nanocrystalline Nd₁₂Fe₈₂B₆ (atomic ratio) alloy powders with Nd₂Fe₁₄B/α-Fe two-phase structure were prepared by HDDR combined with mechanical milling. The as-cast Nd₁₂Fe₈₂B₆ alloy was disproportionated via ball milling in hydrogen, and desorption–recombination was then performed. The phase and structural change due to both the milling in hydrogen and the subsequent desorption–recombination treatment was characterized by X-ray diffraction (XRD). The desorption–recombination behavior of the as-disproportionated alloy was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The morphology and microstructure of the final alloy powders subject to desorption–recombination treatment were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results showed that, by milling in hydrogen for 20 h, the matrix Nd₂Fe₁₄B phase of the alloy was fully disproportionated into a nano-structured mixture of Nd₂H₅, Fe₂B, and α-Fe phases with average size of about 8 nm, and that a subsequent desorption–recombination treatment at 760 °C for 30 min led to the formation of Nd₂Fe₁₄B/α-Fe two-phase nanocomposite powders with average crystallite size of 30 nm. The remanence B_r, coercivity H_c, and maximum energy product (BH)_max of such nanocrystalline Nd₁₂Fe₈₂B₆ alloy powders achieved 0.73 T, 610 kA/m, and 110.8 kJ/m³, respectively.     

The effect of aging time and calcination temperature on the magnetic properties of α-Fe/Fe3O4 composite

Composites of α-Fe/Fe₃O₄ having dimensions in the range of 100–150 nm have been prepared by disproportion method. The structure and morphology are investigated by XRD and TEM. XRD shows that the metal has got the BCC structure. TEM shows balls of metallic iron about 100-nm-wide stuck to magnetite grains. Magnetic measurement shows that the sample aged for 3 h and calcined at 200 °C has the maximal saturation magnetization corresponding to the highest concentration of α-Fe in the final sample.     

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.     

Research on preparing compact bulk nanocomposite Nd2Fe14B/α-Fe magnetic materials by hot extrusion

In this paper, compact bulk nanocomposite Nd₂Fe₁₄B/α-Fe magnetic materials were prepared by hot extrusion of amorphous and nanocrystalline powders, which were prepared by high-energy ball-milling (HEBM) of the Nd₂Fe₁₄ B-type hard magnetic phase with 20 vol% of α-Fe as soft magnetic phase. The extrusion temperature has important influence on magnetic properties and microstructure of magnetic materials. The results show that the grain size of Nd₂Fe₁₄B and α-Fe phase increases steadily with increasing extrusion temperature. Furthermore, optimal extrusion temperature of 1223 K occurs, at which the highest magnetic properties and relative density can be obtained.     

Effect of Cu and Ga additions on the anisotropy of R2Fe14B/α-Fe nanocomposite die-upset magnets (R=Pr,Nd)

Fully dense nanocomposite magnets containing hard R₂Fe₁₄B and soft α-Fe phases were produced from both melt-spun and mechanically milled alloys by hot pressing and subsequent die upsetting. Although R-lean R–Fe–B alloys that do not contain the grain-boundary R-rich phase are known not to be susceptible to texture development by means of die upsetting, we found that small additions of Cu make the texturing possible. The resulting microstructure of oriented platelet grains is similar to that of the R-rich die-upset magnets. Properties of the Cu-containing R₂Fe₁₄B/α-Fe die-upset magnets can be further improved by adding Ga. The anisotropic Pr₁₂Fe₈₀Cu₁Ga₁B₆ magnet made from mechanically milled alloy and containing 17.2 wt% α-Fe had a remanence of 13 kG and a maximum energy product of 23.4 MG Oe. The Pr_11.25Fe_80.75Cu₁Ga₁B₆ magnet made from melt-spun alloy and containing 16.2 wt% α-Fe had a maximum energy product of 19.9 MG Oe. The low coercivity of 3–4 kOe typical for the Cu-containing R₂Fe₁₄B/α-Fe die-upset magnets is due to the relatively coarse α-Fe grains. The latter grains are too large for intergranular exchange interaction, but, nevertheless, they are well coupled with the R₂Fe₁₄B grains by a long-range magnetostatic interaction.     

Influence of deposition temperature on the structural and morphological properties of Be3N2 thin films grown by reactive laser ablation

Be₃N₂ thin films have been grown on Si(1 1 1) substrates using the pulsed laser deposition method at different substrate temperatures: room temperature (RT), 200 °C, 400 °C, 600 °C and 700 °C. Additionally, two samples were deposited at RT and were annealed after deposition in situ at 600 °C and 700 °C. In order to obtain the stoichiometry of the samples, they have been characterized in situ by X-ray photoelectron (XPS) and reflection electron energy loss spectroscopy (REELS). The influence of the substrate temperature on the morphological and structural properties of the films was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The results show that all prepared films presented the Be₃N₂ stoichiometry. Formation of whiskers with diameters of 100-200 nm appears at the surface of the films prepared with a substrate temperature of 600 °C or 700 °C. However, the samples grown at RT and annealed at 600 °C or 700 °C do not show whiskers on the surface. The average root mean square (RMS) roughness and the average grain size of the samples grown with respect the substrate temperature is presented. The films grown with a substrate temperature between the room temperature to 400 °C, and the sample annealed in situ at 600 °C were amorphous; while the αBe₃N₂ phase was presented on the samples with a substrate temperature of 600 °C, 700 °C and that deposited with the substrate at RT and annealed in situ at 700 °C.     

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.     

Influence of heating rate on the crystalline properties of 0.7BiFeO3-0.3PbTiO3 thin films prepared by sol-gel process

0.7BiFeO₃-0.3PbTiO₃ (BFPT7030) thin films were deposited on SiO₂/Si substrates by sol-gel process. The influence of heating rate on the crystalline properties of BFPT7030 thin films were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). XRD patterns of the films showed that a pure perovskite phase exists in BFPT7030 films annealed by rapid thermal annealing (RTA) technique. SEM and AFM observations demonstrated that the BFPT7030 films annealed by RTA at 700 °C for 90 s with the heating rate of 1 °C s⁻¹ could show a dense, crack-free surface morphology, and the films’ grains grow better than those of the films annealed by RTA at the same temperature with other heating rates. XPS results of the films indicated that the ratio of Fe³⁺:Fe²⁺ is about 21:10 and 9:5 for the films annealed by RTA at 700 °C for 90 s with the heating rate of 1 and 20 °C s⁻¹, respectively. That means the higher the heating rate, the higher the concentration of Fe²⁺ in the BFPT7030 thin films.     

Magnetic force microscopy characterization of heat and current treated Fe40Ni38Mo4B18 amorphous ribbons

The domain structure of a magnetostrictive Fe₄₀Ni₃₈Mo₄B₁₈ amorphous ribbon has been studied using magnetic force microscopy (MFM) at room temperature. First, the evolution of the magnetic domain patterns as a function of the annealing temperature has been investigated. In samples heat treated at 250 and 450 °C for 1 h, a transformation from 90° to 180° domain wall has been clearly observed, while the sample heat treated at 700 °C for 1 h showed a magnetic phase fixed by the crystalline anisotropy. Additionally, the evolution of the magnetic domain structure by applying a DC current was recorded by the MFM technique. For current annealed samples at 1 A for 1, 30 and 60 min, a transformation between different domain patterns has been observed. Finally, in samples treated by the current annealing method under simultaneous stress, an increase of the annealing time gives rise to a different magnetic structure arising from the development of transverse magnetic anisotropy.     

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.     

Magnetic characterization of dual phase FeZrB soft magnetic alloy

The magnetic properties and the annealing process of Fe₇₈Zr₇B₁₅ amorphous ribbons are investigated by X-ray diffraction (XRD), differential scanning calorimetry, and vibrating sample magnetometer. The fully amorphous structure of the as-quenched ribbons is confirmed by the XRD pattern. The Curie temperature and the saturation magnetization M_s of the ribbons are 305 °C and 124.3 emu/g, respectively. Annealing at 550 °C can result in an increase in M_s with annealing time due to the increasing crystallized volume fraction of α-Fe phase. The optimized annealing process is established at 550 °C for 20-30 min with maximum M_s of 146.6 emu/g. The morphology of the ribbons annealed at 550 °C is observed by scanning electron microscopy, showing that nanocrystalline α-Fe grains are dispersed in an amorphous matrix.     

Effect of nanoscale thin films of Dy2Fe14B on the magnetic hysteresis characteristics of melt-spun ribbons of Nd2Fe14B

The effectiveness of nanoscale Dy₂Fe₁₄B thin films on coercivity and energy product of melt-spun ribbons of Nd₂Fe₁₄B at high temperatures was investigated. It is hypothesized that the nanoscale Dy-thin film will act as an obstacle for the nucleation of reverse domains and also maximize the energy of domain walls and thereby improve the magnetic performance at high temperatures. Pulsed laser deposition (PLD) of amorphous Dy₂Fe₁₄B layers on Nd₂Fe₁₄B melt-spun ribbons was performed for a nominal thickness of 40 nm. The coated ribbons were then annealed in environmentally controlled quartz furnace at two different cycles (750 °C for 15 min and 900 °C for 2 h) to cause crystallization. Magnetic hysteresis tests conducted at 300 and 400 K revealed that there is small but consistent improvement in the magnetic properties of the coated ribbons annealed at 750 °C for 15 min. However, higher temperature annealing (900 °C for 2 h) drastically reduced the magnetic properties. The incomplete recrystallization of amorphous structure at 750 °C for 15 min and large grain growth and formation of non-magnetic phases at 900 °C for 2 h are believed to be responsible for not meeting the expected magnetic performance.     

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.