Amorphous Fe73 Research Articles

Magnetic Properties and Large Magnetocaloric Effect in Amorphous Fe-Ag-Ni-Zr for Room-Temperature Magnetic Refrigeration

This paper reveals that a partial replacement of Fe by Ni (5%) and/or Ag (2%) in amorphous Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">85-x</sub> Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> (x = 0 and 2) alloys leads to the shift of T toward room temperature (RT) (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> = 308 and 303 K for x = 0 and 2, respectively). Basing on isothermal magnetization data, the magnetic entropy change (ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) of the amorphous alloys was calculated. Their maximum ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> values (|ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> |) achieve just around RT, corresponding to the ferromagnetic-paramagnetic (FM-PM) phase transition of the amorphous phase. Under a magnetic field change of 10 kOe, |ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> | values are ~1 J · kg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> · K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . We have also used different methods, such as the modified Arrott plots, the Kouvel-Fisher method, and critical isotherm analysis to study their critical property around the FM-PM phase transition. Our results suggest that the amorphous Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">85-x</sub> Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> alloys exhibit a second-order magnetic phase transition with the critical exponents of β = 0.389-0.396 and y = 1.279-1.334 close to those expected for the 3-D Heisenberg model. This proves the existence of short-range FM interactions in these alloys.

Nanomechanical characterization of amorphous and nanocrystalline FeCuNbSiB thin films

Mechanical properties (hardness and Young's modulus) of amorphous and nanocrystalline Fe73.5Cu1Nb3Si15.5B7 thin films (thicknesses from 1.4μm to 2μm) have been investigated using the depth-sensing nanoindentation technique. The amorphous films, having uniform and smooth surfaces, were deposited on glass, aluminum, silicon, and sapphire substrates using the high power impulse magnetron sputtering technique. The nanocrystalline state was achieved after isothermal treatments performed at temperatures between 463°C and 475°C. The mean value for the effective Young's modulus of the amorphous Fe73.5Cu1Nb3Si15.5B7 thin films is about 146GPa, regardless of their thickness or the substrate's nature. Increasing the thickness of the films, the hardness value increases up to 1GPa. After the thermal treatments performed at 475°C (when the films’ structure consists of b.c.c. α-Fe(Si) grains with average size of 15nm embedded in a residual amorphous matrix) the effective Young's modulus value decreases by about 13%, while hardness value increases by about 13% with respect to the as-deposited state.

In situ surface magneto-optical Kerr effect (s-MOKE) study of ultrathin soft magnetic FeCuNbSiB alloy films

Herein we report on an in situ surface magneto-optical Kerr effect (s-MOKE) study of ion-beam-sputtered ultra-thin films of an amorphous Fe73.9Cu0.9Nb3.1Si13.2B8.9 (FINEMET) alloy with film growth that ranges from a fraction of a nm to a few tens of nms. Extrapolating the linear variation of the Kerr signal with film thickness suggests the absence of a magnetic dead layer at the substrate/FINEMET film interface, and hence the absence of any intermixing. The presence of a thin SiO2 film at the surface of the Si substrate may be responsible for preventing possible intermixing of Fe with Si to form nonmagnetic silicide. Close to the onset of ferromagnetic ordering, a steep increase in the coercive field with film thickness can be explained in terms of the Volmer–Weber growth of the film. Furthermore, the temperature dependence of the hysteresis loops of a 41 nm-thick FINEMET film has been studied. The Curie temperature of the amorphous film is found to be lower than that of a ribbon of the same composition. The origin of a uniaxial magnetic anisotropy in the as-prepared stage is attributed to the generation of some long-range stresses in the film, which are relieved close to the onset temperature for nanocrystallization.

Solvothermal synthesis of pyrite FeS2nanocubes and their superior high rate lithium storage properties

Iron pyrite nanocubes with particle sizes of around 80–120 nm have been synthesized via a facile solvothermal method. Time-dependent characterization found that the iron(II) chloride and sulfur precursors first react to form sheet-like amorphous Fe1−xS, which transforms into pyrite FeS2 nanocubes upon further heating. As an anode material for lithium ion batteries, the as-synthesized pyrite FeS2 nanocubes were found to deliver a reversible discharge capacity of 540 mA h g−1 after cycling for 150 cycles at a current density of 1 A g−1. Even at higher current density of 5 A g−1, the pyrite FeS2 electrode still managed to give a stable discharge capacity of about 220 mA h g−1. The enhanced lithium storage properties are attributed to its higher specific surface area that can provide more lithium ion (Li+) reaction sites, leading to less polarization and better cycling performance.

Surface Properties of a Nanocrystalline Fe–Ni–Nb–B Alloy After Neutron Irradiation

Abstract The effect of neutron radiation on the surface properties of the nanocrystalline (Fe0.25Ni0.75)81Nb7B12 alloy was studied. Firstly, amorphous (Fe0.25Ni0.75)81Nb7B12 ribbon was brought by controlled annealing to the nanocrystalline state. After annealing, the samples of the nanocrystalline ribbon were irradiated in a nuclear reactor with neutron fluences of 1×1016cm−2 and 1 × 1017cm−2 . By utilizing the magnetic force microscopy (MFM), topography and a magnetic domain structure were recorded at the surface of the ribbon-shaped samples before and after irradiation with neutrons. The results indicate that in terms of surface the nanocrystalline (Fe0.25Ni0.75)81Nb7B12 alloy is radiation-resistant up to a neutron fluence of 1 × 1017cm−2 . The changes in topography observed for both irradiated samples are discussed

The Influence of Vanadium on Magnetism and Magnetocaloric Properties of Fe 8 0 − x V x B12Si8 (x = 8, 10, and 13.7) Amorphous Alloys

Amorphous soft magnetic Fe80−x VxB12Si8 ribbons (0 ≤ x ≤ 14) have been fabricated by melt spinning technique, and their magnetic and magnetocaloric properties have been studied. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. The addition of vanadium to the ternary Fe80B12Si8 alloy results in a decrease of the Curie temperature of amorphous alloys, TC, from 473.5 to 335 K. With an increasing V content, the average magnetic moment of Fe atom and the magnetic entropy change also decrease. Fe66.3V13.7B12Si8 alloy exhibits the highest refrigeration capacity of 93.7 J kg−1 and moderate peak magnetic entropy of 1.034 J kg−1 K−1 (TC = 335 K) under the maximum applied field of 2 T. The results from this work showed that V containing amorphous alloy 13.7 at. % is an interesting material and potential candidate for magnetic refrigerants working near room temperature. The observed −ΔSMmax values compare favorably with other amorphous Fe-based alloys.

Corrosion Resistance of FeSiB and FeCuNbSiB Alloys and Its Influence on Their Soft Magnetic Properties in NaOH Solution

Abstract Amorphous Fe78Si9B13 and nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloys with low coercivity, high saturation magnetic flux density and high permeability have attracted extensive attention. In this paper the influence of corrosion on their soft magnetic properties of Fe78Si9B13 and Fe73.5Cu1Nb3Si13.5B9 alloys tested in the NaOH solution (pH=9∼10) was investigated. Changes of soft magnetic properties including effective permeability, coercivity and saturated magnetic flux density were analyzed. The samples were characterized by X-ray diffraction and 3D high depth of field microscope. The results show that some orange precipitates corresponding to an iron oxide are produced in the solution after corrosion, and the structures of Fe78Si9B13 and Fe73.5Cu1Nb3Si13.5B9 alloys remain unchanged. The soft magnetic properties of these alloys decrease after corrosion. The decrease of effective permeability μe and saturated magnetic flux density Bs, after corrosion, observed in the amorphous Fe78Si9B13 sample, was larger than that observed in the nanocrystalline Fe73.5Cu1Nb3Si13.5B9 sample.

Effect of Si addition on the corrosion properties of amorphous Fe-based soft magnetic alloys

Effects of an addition of Si and P into amorphous Fe85.2B14Cu0.8 based soft magnetic alloys were investigated in boric-borate buffer solution. The addition of P decreased the passive current density effectively. Substituting Si for P in Fe85.2SixB9P5−xCu0.8 (x=0, 1, 2at.%) alloys further improved corrosion resistance. After the removal of the oxide films, the passive current density was higher than those covered by the oxide films. The lowest passive current density was observed at 5×10−6A/cm2 on the Fe85.2Si1B9P4Cu0.8 alloy. On the other hand, the pitting potential of the alloys before and after removal of the oxide films was as high as about 0.96V and was independent of chemical composition of the alloys. The addition of Si and P could enhance the corrosion resistance of Fe85.2SixB9P5−xCu0.8 alloys via modification of the chemical composition of the oxide films. Cyclic voltammetric results indicated that the addition of Si suppressed the formation rate of bivalent Fe species, which slows down reaction rates of this rate-determining step.

The Effect of Nb Content on the Thermal, Structural, and Magnetic Properties of FeNbB Ribbons

Amorphous Fe80−xNbxB20 (x = 5, 10, 15) ribbons were prepared by single-roller melt spinning method. The thermal, structural and magnetic properties of Fe80−xNbxB20 (x = 5, 10, 15) ribbons were investigated using di erential thermal analysis, X-ray di raction, and vibrating sample magnetometer. The thermal stability is the lowest for Fe70Nb10B20 ribbon and the highest for Fe65Nb15B20 ribbon. Along with the increase of Nb content, the supercooled liquid region ∆Tx increases, indicating that the amorphous formation ability improves. The primary stages of crystallization of the three ribbons are di erent. The primary devitri cation phases are Fe23B6 type for Fe70Nb10B20 and Fe75Nb5B20 ribbons, and α-Fe type for Fe65Nb15B20 ribbon. Fe80−xNbxB20 (x = 5, 10) ribbons are ferromagnetic and the Fe65Nb15B20 ribbon is paramagnetic. The saturation magnetization (M s) decreases with increasing Nb content.

Kinetics and mechanism of thermally induced crystallization of amorphous Fe73.5Cu1Nb3Si15.5B7 alloy

Abstract Thermal stability of amorphous Fe73.5Cu1Nb3Si15.5B7 alloy and its crystallization kinetics and mechanism have been investigated. The alloy is stable up to 748 K, after which it undergoes multi-step crystallization with formation of α-Fe(Si)/Fe3Si, Fe2B, Fe16Nb6Si7, and Fe2Si crystalline phases. The crystallization occurs in two distinct and well separated complex processes, each corresponding to formation of two phases. Activation energy for the formation of the latter two phases is significantly higher, due to their formation out of the previously formed iron–silicon crystalline phase. By comparison of Avrami exponents of experimental system and a hypothetical system where no impingement occurs, the influence of impingement on reaction mechanism was successfully isolated. While the reaction mechanism was suggested as volume diffusion controlled growth of α-Fe(Si) and Fe2B phases, and interface-controlled growth of Fe16Nb6Si7 and Fe2Si phases, impingement plays an increasingly significant role as the crystallization progresses. The determined value of kinetic triplet was used to calculate the alloy lifetime, showing its resistance against crystallization.

Effect of laser processing on the structure and magnetic characteristics of an amorphous Fe73.5Nb3Cu1Si15.5B7 alloy

We have studied the effect of pulsed laser irradiation on the microstructure of the Fe73.5Nb3Cu1Si15.5B7 alloy at pulse durations in the range 10−7 to 10−5 s. At pulse durations shorter than 2 × 10−5 s, no crystalline phases have been detected. We have determined the threshold incident laser intensity as a function of pulse duration. The slope of the magnetization curve of the alloy has been shown to be influenced by laser processing conditions. We have determined the Curie temperatures of the alloy in its amorphous and crystalline states and the crystallization onset temperature of the amorphous alloy.

Influence of structurization of amorphous Fe73.5Si13.5B9Nb3Cu1 alloy on its spectral properties

The optical properties of Fe73.5Si13.5B9Nb3Cu1 ferromagnetic alloy in the amorphous, nanocrystalline, and crystalline states have been investigated by optical ellipsometry in the spectral range of 0.22–18 μm. It is established that the crystallization of alloy during heat treatment leads to a significant change in its optical constants, as well as the frequency dependences of dielectric functions calculated based on these constants. The structural ordering is accompanied by a considerable increase in the intensity of the fundamental absorption band and an occurrence of its blue shift. Some characteristics of conduction electrons are determined, the numerical values of which also depend on the degree of atomic order.

A facile approach for the synthesis of stable amorphous nanoscale zero-valent iron particles

Conventional methods for the preparation and stabilization of amorphous nanoscale zero-valent iron (NZVI) particles are complicated and costly. In this study, a facile and economic approach for synthesizing stable NZVI without the requirement of vacuum condition was explored. NZVI particles were simultaneously prepared and stabilized in non-deoxygenated aqueous solutions. Scanning electron microscopy, energy dispersive xray microanalysis (EDX), and x-ray photoelectron spectroscopy results showed that the as-prepared Fe0 were uniform spherical particles with a diameter ranging from 50 nm to 100 nm and a ∼5 nm thick oxide shell. The x-ray diffraction (XRD) patterns indicated that the main component of the particles was amorphous Fe0. As confirmed via EDX and XRD analyses, the Fe0 content in the stabilized NZVI particles was hardly changed after six months of storage in dry atmosphere.

Study on Positron Annihilation Lifetime of Amorphous Alloy Fe&lt;sub&gt;73.5&lt;/sub&gt;Cu&lt;sub&gt;1&lt;/sub&gt;Nb&lt;sub&gt;3&lt;/sub&gt;Si&lt;sub&gt;13.5&lt;/sub&gt;B&lt;sub&gt;9&lt;/sub&gt; by Magnetic Pulse Treated

The effect of magnetic pulse treatments on Fe73.5Cu1Nb3Si13.5B9 amorphous alloy prepared by melt-spun technique is investigated. The structural defects of the treated specimens are investigated by position annihilation lifetime spectra. The results show that amorphous alloy Fe73.5Cu1Nb3Si13.5B9 have two kinds of free volume. One is Bernal vacancy-like which is characterized by less than an atomic volume, Another is void-like defect. Under the applied pulsed magnetic field, the annihilation lifetime and the relative intensity of treated specimens is decrease because the crystallization phase separate out from the amorphous matrix. The relative intensity I2 is increase because the larger free volumes appear at grain boundary of Cu and Nb enrichment area.

Study of amorphous phase in Fe100−x(NbTiTa)x alloys synthesized by mechanical alloying and its effect on the crystallization phenomenon

Amorphous Fe100−x(NbTiTa)x (x=20, 30 and 40) alloy powders without metalloids were synthesized from commercially available pure elemental powders by mechanical alloying. Microstructure, glass-forming ability, thermal stability and crystallization kinetics of the as-milled powders were analyzed by SEM, XRD, DSC and TEM. Results show that Fe60(NbTiTa)40 has the best glass forming ability with ΔTx=101K, which could be explained by appropriate atomic-size mismatch and large negative heat of mixing among main constituent elements. The non-isothermal crystallization kinetics were analyzed. The values of the Avrami exponent (n) suggest that the crystallization of Fe60(NbTiTa)40 and Fe70(NbTiTa)30 amorphous alloy powders is governed by volume diffusion-controlled two-dimensional growth and three-dimensional growth, respectively. The materials obtained in this research provide good candidate for fabricating bulk Fe-based amorphous alloys and related bulk nanocrystalline materials through powder metallurgy methods.

Nanocrystallization kinetics and magnetic properties of the melt spun amorphous (Fe0.5Co0.5)77Si11B9Cu0.6Nb2.4 alloy

Kinetics of crystallization in an amorphous (Fe0.5Co0.5)77Si11B9Cu0.6Nb2.4 (at.%) alloy was investigated using differential scanning calorimetry (DSC). Transformed fraction as a function of temperature was obtained by accurate DSC measurement and the experimental data analyzed with Vyazovkin model-free kinetic method. Reconstructed form of the experimental kinetics model, g(α), clearly showed the crystallization mechanism do not belongs to a single model but almost follows the Avrami-Erofe’ev. Magnetic coercivity and hysteresis loss values of the annealed samples at 823K were 7.5Am−1 and 1.2Jm−3, compared to 17.1Am−1 and 37.1Jm−3 for as spun samples. Magnetic measurements show the annealing reduces both coercivity and hysteresis loss at all frequencies.

Fe-based nanocrystalline powder cores with ultra-low core loss

Melt-spun amorphous Fe73.5Cu1Nb3Si15.5B7 alloy strip was crushed to make flake-shaped fine powders. The passivated powders by phosphoric acid were mixed with organic and inorganic binder, followed by cold compaction to form toroid-shaped bonded powder-metallurgical magnets. The powder cores were heat-treated to crystallize the amorphous structure and to control the nano-grain structure. Well-coated phosphate-oxide insulation layer on the powder surface decreased the the core loss with the insulation of each powder. FeCuNbSiB nanocrystalline alloy powder core prepared from the powder having phosphate-oxide layer exhibits a stable permeability up to high frequency range over 2MHz. Especially, the core loss could be reduced remarkably. At the other hand, the softened inorganic binder in the annealing process could effectively improve the intensity of powder cores.

Tuning magnetic properties by hydrogen implantation in amorphous [formula omitted] thin films

Thin films of amorphous Fe100−xZrx(x=7.6–12.9at%) were synthesized by dc-magnetron sputtering. Samples with compositions of x=11.6 and 12.0at% were hydrogenated by implantation. The Curie temperature increases with hydrogen content from 232K for as-grown Fe88Zr12 to 370K for a sample hydrogenated to 31at%. The coercivity decreases dramatically upon hydrogenation, yielding films with tunable transition temperatures and soft magnetic properties.

Effects of chemical composition on nanocrystallization kinetics, microstructure and magnetic properties of finemet-type amorphous alloys

In this study, the kinetics of nanocrystallization of amorphous Fe73.5Si13.5B9Nb3Cu1 (F1) and Fe77Si11B9Nb2.4Cu0.6 (F2) alloys is investigated. The microstructure and magnetic properties of the nanocrystalline alloys are compared. The crystallization temperature of F2 alloy is shifted towards lower temperatures with respect to F1. Thus, the crystalline volume fraction and the crystalline grain size at specific annealing temperature for the F2 alloy are higher than for the F1 alloy, accounting for the higher coercive force of F2 alloy with respect to the one of F1 alloy. According to isoconversional methods, the activation energy for crystallization is variable as a function of transformed fraction because of the continuous changes in chemical composition during the transformation. Mean values of 350 and 290 kJ/mol are obtained for F1 and F2, respectively. Microstructural observations confirm that minor changes in chemical composition affect the kinetics and final microstructure of the nanocrystalline alloy, that determine the observed magnetic properties.

Stress Dependence of Switching Field during the Devitrification of Finemet-Based Magnetic Microwires

We have studied the influence of the thermal treatment on the stress dependence of the switching field during the devitrification of amorphous Fe73.5Cu1Nb3Si11.5B11 microwires. The non-destructive test (NDT) method based on the magnetization reversal of ferromagnetic materials is sensible to changes in microstructural characteristics and the stress state of the material. The stress dependence has been explained considering the magnetoelastic contribution to the switching mechanism which is modified applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses distribution through thermal treatments. We show that by properly setting a frequency during the measurement and adequate treatment of the sample, it is possible to vary the sensitivity, magnitude and stress dependence of the sample. Keywords: Magnetic bistability, glass-coated microwires, switching field, stress sensor