Soft magnetic properties of amorphous Fe52Co34Hf7B6Cu1 alloy treated by pulsed magnetic field and annealing

<正>The crystallization,microstructure,and soft magnetic properties of Fe₅₂Co₃₄Hf₇B₆Cu₁ alloy are studied.Amorphous Fe₅₂Co₃₄Hf₇B₆Cu₁ alloys are first treated by a pulsed magnetic field with a medium frequency,and then annealed at 100℃-400℃for 30 min in a vacuum.The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer.The soft magnetic properties of specimens are measured by a vibrating sample magnetometer（VSM）.The microstructure changes of specimens are observed by a Mossbauer spectroscopy and transmission electron microscope（TEM）.The results show the medium-frequency pulsating magnetic field will promote nanocrystallization of the amorphous alloy with a lower temperature rise.The nanocrystalline phase isα-Fe（Co） with bcc crystal structure,and the grain size is about 10 nm.After vacuum annealing at 100℃for 30 min,scattering nanocrystalline phases become more uniform,the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.     

Effect of crystallization of amorphous Fe5Co75Si4B16 alloy on its optical properties

The optical properties of ferromagnetic Fe₅Co₇₅Si₄B₁₆ alloy in the amorphous state and after temperature treatments have been investigated by spectroscopic ellipsometry in the energy range of 0.073–5.64 eV. It is shown that alloy crystallization changes significantly the frequency dependences of the optical constants and the dielectric functions calculated based on them. The atomic ordering is accompanied by a significant increase in the intensity of the fundamental band of quantum light absorption. The plasma and relaxation frequencies of conduction electrons have been calculated.     

Investigation of the magnetic characteristic of amorphous Fe40Ni40B20 and Fe6Co70Ni13Si7B4 foils by a magnetooptical method

Magnetic parameters, the local anisotropy field H_k, the effective field h related to the correlation radius, and the coercive force H_c, are determined for free and contact surfaces by investigating the magnetization curves of amorphous Fe₄₀Ni₄₀B₂₀ and Fe₆Co₇₀Ni₁₃Si₇B₄ foils by a highly-sensitive method of measuring the magnetooptical phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 49–52, November, 1989.     

退火处理Fe43Co43Hf7B6Cu1非晶合金的正电子湮没研究

对熔体急冷法制备的Fe₄₃Co₄₃Hf₇B₆Cu₁非晶合金进行了200,300,400和500 ℃保温30 min的退火处理,用正电子湮没寿命谱、X射线衍射、穆斯堡尔谱等方法研究了退火后试样的结构及结构缺陷变化.结果表明,在非晶合金的制备态,正电子主要在非晶基体相空位尺寸的自由体积中湮没,湮没寿命τ₁为158.4 ps,强度I₁关键词： 43Co₄₃Hf₇B₆Cu₁非晶')" href="#">Fe₄₃Co₄₃Hf₇B₆Cu₁非晶 退火处理 正电子湮没寿命 结构与结构缺陷     

Phase segregation in the Fe90Zr10 amorphous alloy under heating

A study of the changes in the structure of melt-quenched Fe₉₀Zr₁₀ amorphous alloys by x-ray diffraction, Auger spectroscopy, and transmission electron microscopy is reported. The samples were subjected to isochronous (for 1 h) and isothermal anneals at 100–650 °C. It is shown that an amorphous alloy annealed for one hour at 300–500 °C crystallizes with formation of a supersaturated solid solution of Zr in α Fe and the intermetallic compound Fe₃Zr. Isothermal anneal at 100 °C for up to 7000 h produces nanocrystallites 110–30 nm in size, with fuzzy interfaces between the grains. An alloy subjected to such an anneal contains two solid solutions of Zr in Fe, having a cubic and a weakly tetragonal lattice. Crystallization taking place during low-temperature anneals is preceded by phase segregation of the alloy within the amorphous state. The lattice periods of the solid solutions have been determined. The possibility of the alloy crystallizing by spinodal decomposition during prolonged annealing is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1769–1772 (October 1998)     

A potential Co36Fe36Si4B20Nb4 nanocrystalline alloy for high temperature soft magnetic applications

The paper addresses the structural, crystallization, soft magnetic and Curie temperature behaviour of Co₃₆Fe₃₆Si₄B₂₀Nb₄ alloy. The material, prepared in the form of ribbons by melt-spinning technique, was amorphous in the as-cast state. Differential scanning calorimetry (DSC) showed two stages of crystallization whereas thermal variation of electrical resistivity (TER) carried out to a higher range of temperature indicated three stages of crystallization. The first crystallization stage, which occurred at 845?K and 825?K in DSC and TER, respectively, was due to the formation of nanophase (CoFe)₂Si as evidenced by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The formation of these nanoparticles reduced the magnetocrystalline anisotropy, thereby revealing good soft magnetic properties in the samples annealed between 825?K and 875?K with coercivity less than 49.9?A?m^?1 (627?mOe) and susceptibility?～?0.72?×?10³. In this optimum nanocrystalline state, the material also exhibited a high Curie temperature above 1100?K, opening the scope of the present nanocrystalline alloy for high temperature applications.     

Hyperfine interactions in amorphous and nanocrystalline Fe80Ti7Cu1B12 alloy

⁵⁷Fe Mössbauer spectroscopy is used to elucidate the nature of the hyperfine interactions present in amorphous and nanocrystalline forms of Fe₈₀Ti₇Cu₁B₁₂ alloy. Two mutually independent distributions of hyperfine fields and one sextet of Lorentzian lines are employed to reproduce the broad (atoms in amorphous rest and interface zone) and narrow (ordered) parts of the spectra, respectively. The presented conclusions are derived from three-dimensional mapping of the hyperfine field distributions corresponding to both amorphous and interfacial spectral components. The individual distributions are decomposed into Gaussian components which characterize different types of hyperfine interactions.     

Nanoporosity and magnetic performance of Fe58Ni20Si9B13 amorphous metallic alloy

The structure and magnetic properties of this amorphous alloy are studied. The structure was varied by applying a hydrostatic pressure of 10 kbar. By means of small-angle x-ray diffraction analysis, two fractions of nanopores (30 and 140 nm in size) are revealed. The pressure decreases the size of nanopores and raises their mean spacing. As a result of pressure application, the maximal magnetic induction grows, in contrast to the remanent induction. A correlation between the magnetic properties and nanoporosity of the alloy is discussed.     

Changes of thermal, mechanical and magnetic properties of an amorphous Fe80Cr5B15 alloy during magnetic and structural phase transitions

Thermal, mechanical and thermomagnetic properties associated with the magnetic and structural transition of an amorphous Fe₈₀Cr₅B₁₅ alloy are described. The investigation was carried out in a simultaneous dilatometric and thermomagnetic experiment. An anomaly of the thermal expansion coefficient at the Curie point and a change in mechanical properties just before the onset of crystallization are observed. The results are compared with the thermal behavior obtained by differential scanning calorimetry.     

Low-temperature crystallization of the Fe−Co−B amorphous alloys

Low-temperature crystallization of the melt-spun amorphous ribbon Fe₆₄Co₂₁B₁₅ was measured by the⁵⁷Fe Mössbauerin situ scanning method in the temperature range of about 300 to 350°C. Least-squares fit of the time-dependent α-Fe?Co isothermal absorption intensity revealed up to three superimposed exponential processes. Taking into account that this method indicates the content of the crystallized metallic phase only, then the first two (nucleation and primary crystallization) processes are followed by a rather slow third one, which could only mean the decay of metastable (Fe, Co)₃B having a thermally activated character as well. Besides confirming the previously reported activation enthalpies for the two faster processes, that of the slowest one was determined as (450±10) kJ/mol.     

Crystallization kinetics of the Fe−Co−B amorphous alloys

A series of amorphous ribbons Fe_85−x Co _x B₁₅ was subjected to the isothermal crystallization annealing. The alloys forx=12, 15, 17, 19, 21, 23, and 25 at.% Co were measured at room temperature by standard transmission technique during interrupted annealing. The samples with 12 and 21 at.% Co were used for direct scanning at constant velocity of the outermost metallic peak. In both cases gradually increasing content of the metallic Fe−Co phase was observed in at least two stages. Several scanning temperatures applied with the 12 and 21 at.% Co samples made it possible to draw the Arrhenius plots and to estimate the activation enthalpies of the processes. By analysing the Avrami exponents and activation enthalpies, the first process is attributed to a comparatively fast primary Fe−Co crystallization followed by the transformations of the amorphous rest.     

Re-entrant magnetic behaviour in amorphous Fe-rich Fe100−x Zr x alloys

We report results of⁵⁷Fe Mössbauer measurements on the magnetically concentrated re-entrant amorphous Fe₁₀₀?xZr _x alloys (8≤x≤12) which give convincing evidence for a microscopic origin of the low-temperature magnetization anomaly atT _f<T _c. This is shown by an anomalous increase in the magnetic hyperfine field and in the relative intensities of the (?m=0)-Mössbauer lines belowT _f upon cooling. No evidence was found for an antiferromagnetic phase. The shape of the hyperfine-field distribution atT=4.2 K in zero external field and in a field of 3 T is unchanged, indicating homogeneous behaviour of all Fe moments near saturation. Ferromagnetic order is not long-ranged, but determined by exchange-coupled magnetic clusters. The cluster moment nearT _c is found to decrease strongly with increasing Fe content and extrapolates to zero atx≈96.     

Effect of structural disorder on magnetic frustrations in the Fe80Nb6B14 amorphous alloy

The paper presents measurements of magnetic frustrations for the Fe₈₀Nb₆B₁₄ amorphous alloy preliminary annealed for 1 h at temperatures ranging from 300 to 770 K in comparison with other parameters characterizing structural relaxation. It was shown that annealing out of free volume and internal stresses cause a reduction in number of frustrated states observed in the range 400>T>50 K. In the range 2<T<50 K additional frustrations due to iron clusters or nanograins were detected.     

Magnetic and magnetoelastic properties of Fe64Co21B15 and Fe73Co12B15 amorphous metal strips

The effect of magnetic annealing on the magnetic and magnetoelastic properties of FeCoB amorphous metal strips in the temperature range from 290 to 380°C has been investigated. With the method of photostimulated exoelectronic emission it has been found that in this temperature range there occurs crystallization of the surface of the test strips. It has been shown that the minima of the coercive force, residual induction, and differential magnetic permeability and the maximum absolute values of the negative Δ-effect are attained at magnetic annealing temperatures close to the temperatures corresponding to the maxima of the intensity of photostimulated exoelectronic emission. An explanation of the results obtained has been proposed which is based on the notions about the effect of internal stresses on the induced magnetic anisotropy of the test strips. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 59–65, August, 2006.     

Effect of mechanical tension on electrical transport properties of amorphous Fe92Zr8 alloy

The effect of mechanical tension and magnetic field on the electrical resistivity of amorphous Fe₉₂Zr₈ alloy has been studied as a function of temperature. The results show that resistivity is enhanced by the applied tension and magnetic field. The increase in the electrical resistivity is attributed to volumetric effect, disorder scattering and thermal vibrations. The observed increase in the Curie temperature caused by the applied stress was found to be about 7×10^–6 °C/PA and indicates that some structural changes occurred.     

Effect of silicon additions on the magnetic properties of Nd2Fe12Co2B alloy

The results of magnetic measurements performed on Nd₂Fe_12−xSi_xCo₂B alloys with 0⩽x⩽0.6 are presented. All the compound studied crystallize in the tetragonal Nd₂Fe₁₄B structure. The unit cell volume is found to decrease by introducing Si. With substitution of Fe by Si, the saturation moments decrease, but theanisotropy fields and Curie temperatures are found to increase significantly. For example, in Nd₂Fe_11.5Si_0.5Co₂b, at room temperature, μ_s=28.4μ_B, H_A=80 kOe and T_c=736 K.