Amorphous Magnetic Alloys Research Articles

The use of conducting polymers as cathodes for the electrochemical deposition of magnetic transition metal/rare earth alloys

We report the electrodeposition of Cu and Ni in aqueous solutions together with the deposition of lanthanides (Gd, Sm, Dy, Tb) and amorphous magnetic alloys of lanthanides with transition metals (Fe, Co) onto various polymer cathodes in formamide solutions. We used conducting polymers (polypyrrole, PPy; polyethylenedioxythiophene, PEDOT) sprayed on different substrates and in addition composite materials based on carbon black (CB) mixed either with polyethylene (PE) or with polycarbonate (PC). In the latter case, the conducting material is easily shaped out in various forms. When deposited on some of these substrates, the alloys appear as an interesting material for magneto-optic recording. The electrochemical process was used for the preparation of Gd/Co and Dy/Fe alloys for which the measured coercitive fields ranged from 250–300 Oe (Dy/Fe) to about 350 Oe (Gd/Fe). We demonstrated also the feasibility of an additional electrografting of a transparent protective layer of polyacrylonitrile (PAN) in order to avoid the corrosion of the alloys by the atmosphere.

The relationship between microstructure and field-induced anisotropy in cobalt-rich amorphous alloys after magnetic field annealing

We have made a comparative microstructural study of field annealed Co 95−xFe 5(BSi) x amorphous alloys using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Until recently, it was generally assumed that amorphous magnetic alloys respond to field annealing by a process of local directional ordering which leaves the amorphous structure intact. However, striking differences in the microstructural morphology after field annealing were revealed for different glass former ratios B/Si. For high B/Si ratios, the surface crystals are predominantly fcc Co and demonstrate a high density of oxygen faults. For low B/Si ratios, the surface crystals are predominantly hcp Co and almost free of faults. Response to field annealing is proportional to the B/Si ratio and correlates with the presence of oxygen faults in surface crystals. These observations appear to be related to those of Nesbitt and Heidenreich (E.A. Nesbitt, R.D. Heidenreich, J. Appl. Phys. 30 (1959) 1000–1003) in perminvar alloys where oxygen was found to be necessary for field annealing to be effective.

Fe-based soft magnetic amorphous alloys with a wide supercooled liquid region

Amorphous alloys with a wide supercooled liquid region (ΔTx) before crystallization were formed in the Fe56Co7Ni7Hf8M2B20 (M=Nb, Ta) alloys by melt spinning. The ΔTx which is a critical factor of glass-forming ability, increases to large values exceeding 90 from 82 K by the addition of 2 at. % M, and the largest ΔTx value is larger by about 10 K than the largest value for recently reported (Fe,Co,Ni)–Zr–M–B alloys. By the addition of the M metals, magnetic properties also changed. Good soft magnetic properties were obtained for the alloys annealed for 300 s at 800 K. The saturation magnetization (Is), coercive force (Hc), and effective permeability (μe) at 1 kHz are, respectively, 0.71 T, 1.0 A/m, and 16 700 for the M=Nb alloy and 0.76 T, 1.0 A/m, and 15 600 for the M=Ta alloy. The finding of the Fe-based amorphous alloys exhibiting simultaneously the wide supercooled liquid region before crystallization and the good soft magnetic properties seem to enable the future development of a new ferromagnetic bulk amorphous alloy.

Evidence for polarised boron in Co-B and Fe-B alloys

By exploiting the tunability of synchrotron radiation in measurements of spin-resolved photoemission it has proved possible to obtain information on the polarisation of the valence electrons of Co-B and Fe-B amorphous magnetic alloys. Both the spin-integrated and spin-resolved energy distribution curves show a marked dependence on photon energy indicating that the p states of boron hybridise with the d states of the transition metals giving rise to mixed states in the binding energy range 1 to 5 eV. The observed polarisation and spin-resolved densities of states imply that in the above restricted energy range there is a net negative polarisation of the boron states.

Cooling treatment effects on soft magnetic amorphous alloys properties.

The influence of the low temperature treatment on the physical properties of the Fe- and Co-based amorphous alloys was investigated. The mechanical, magneto-optical and magneto-static parameters of these alloys were measured before and after cooling. Irreversible changes in parameters were found.

Ferromagnetic Co–Fe–Zr–B amorphous alloys with glass transition and good high-frequency permeability

A Co-based amorphous phase with glass transition and supercooled liquid region before crystallization was formed in Co70−xFexZr10B20 and Co72−xFexZr8B20 alloys containing more than 14 at % Fe. The crystallization temperature (Tx) is 899 K for the Co–Zr–B alloys and remains unchanged in the Fe concentration range up to 20%. The glass transition temperature (Tg) decreases with increasing Fe content, and the ΔTx(=Tx−Tg) increases from 25 K at 14% Fe to 34 K at 21% Fe. The amorphous alloys with glass transition crystallize with a single stage precipitation of bcc Fe(Co) and Co3ZrB2 phases. The Co-rich amorphous alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.58–0.83 T, low coercivity of 4.7–8.3 A/m, and high permeability of 5500–18 300 in the frequency range of 1–103 kHz and low magnetostriction between −1.5×10−6 and +10×10−6 including zero. The success in synthesizing the soft magnetic amorphous alloys with high stability of supercooled liquid is promising for the future development of ferromagnetic Co-based bulk amorphous alloys.

Mechanisms of the influence of electroinsulation coatings on the magnetic properties of amorphous soft magnetic alloys

The influence of organic and inorganic coatings on the magnetic properties of amorphous Fe-B-Si-C and Fe-Co-Si-B alloys were investigated. The samples of these alloys were in as-quenched state and after heat treatment with or without magnetic field. The morphology of researched coatings was different: amorphous and crystal. The suggested mechanism of the influence of coating is connected with appearance of anisotropic pseudo - uniaxial stresses in a plane of ribbon which are caused by anisotropic arrangement of coating elements in surface of ribbons.

Domain structure destabilization of amorphous soft magnetic alloys with the Curie temperature above the crystallization temperature

A new method of the domain structure destabilization - thermomagnetic treatment (TMT) in high frequency magnetic field is applied to Fe 60 Co 20 Si 5 B 15 amorphous alloy with the Curie point above the crystallization temperature. It is shown that TMT leads to improvement of the alloy magnetic properties.

Thermal analysis in nanostructured alloys obtained by Co-based amorphous ferromagnets

We are dealing with thermal and magnetic properties of nanostructured materials obtained by suitable thermal treatments of soft magnetic Co-based amorphous alloys of Metglas 2714A and Vitrovac 6025 below their conventional crystallization temperature. The ultrafine grain structures lead to superior soft magnetic properties: in homogeneously nanostructured samples of Metglas 2714A the average grain size giving the best soft magnetic properties is of about 2 nm, while in Vitrovac 6025 is about 10 nm. In soft nanostructured samples, structural and magnetic transitions are studied by means of differential thermal analysis, by thermogravimetry with low and non uniform magnetic field and by means of magnetization behavior as a function of the temperature. The results are compared with those of the precursor amorphous alloys and may be justified on the basis of the random anisotropy model generalized for two magnetic phase systems.

Preparation of uranium-based magnetic amorphous alloys by RF sputtering

The effects of amorphization on ferromagnetic uranium compounds UGe 2 and UGa 2 were investigated. The amorphous alloys a-UGe 2 and a-UGa 2 were successfully produced by radio frequency (RF) sputtering. The ferromagnetic exchange of a-UGe 2 is comparable with the crystalline compound. On the contrary, the ordering temperature and the magnetic moment of a-UGa 2 are strongly reduced. The magnetic responses and the electron-transport properties of the alloys are different from those of the ferromagnetic crystalline counterparts, because the collinear spin arrangement was scattered by the random anisotropy originating from the orbital angular momentum of uranium ions.

New amorphous phase formation during amorphous state decay in soft magnetic amorphous alloy

Decay of amorphous alloys of metal-metalloid type from the initial state up to surface crystallization under thermal action has been studied for three different alloys based on Fe- Ni, Fe-Co and Fe-Ni-Co. Temperature dependences of their mechanical, magnetic, magneto-optical and heat properties have been investigated. Embrittlement is established as two stage process for all alloys under consideration. Nature of microscopic process determining the changes of the amorphous alloys macroscopic properties has been established from magnetic, magneto-optical and heat measurements. Experimental data obtained by above mentioned methods let us to argue the formation of new amorphous phase clusters in the embrittled layers.

New load cells and torque meters based on soft magnetic amorphous alloy wires

In this paper we illustrate new kinds of load cells and torque meters based on the properties of soft magnetic materials. The proposed sensors are based on the magnetostrictive delay line (MDL) technique as well as the magneto-inductive (MI) principle. The obtained results show a monotonic and unhysteretic response of the corresponding kinds of sensors.

Wide supercooled liquid region and soft magnetic properties of Fe56Co7Ni7Zr0–10Nb (or Ta)0–10B20 amorphous alloys

An amorphous phase with a wide supercooled liquid region before crystallization was formed in Fe56Co7Ni7Zr10−xMxB20 (M=Nb or Ta, x=0–10 at. %) alloys by melt spinning. The glass transition temperature (Tg) and crystallization temperature (Tx) increase by the dissolution of 2% M and the degree of the increase is larger for Tx, leading to maximum ΔTx(=Tx−Tg) of 85 K at 2% Nb and 87 K at 2% Ta which are larger by about 20 K than the largest value for newly developed Fe–(Al, Ga)–(P,C,B,Si) amorphous alloys. The crystallization of the Nb-containing alloys occurs through two stages of amorphous (Am)→Am′+α-Fe+γ-Fe+Fe76Nb6B18 →α-Fe+γ-Fe+Fe76Nb6B18+Fe2Zr in the range less than about 6% Nb and Am→Am′+γ-Fe→γ-Fe+Co3Nb2B5+Ni8Nb in the range above 8% Nb. The change in the crystallization process with Nb content seems to reflect the easy precipitation of γ-Fe by the increase in the number of Fe–Nb pairs with weaker bonding nature as compared with the Fe–Zr pairs. The best soft magnetic properties were obtained at 2% Nb or 8% Ta. The saturation magnetization, coercive force, effective permeability at 1 kHz, and saturated magnetostriction in the annealed state for 300 s at 800 K are, respectively, 0.96 T, 2.0 A/m, 19 100, and 10×10−6 for the 10% Zr alloy, 0.75 T, 1.1 A/m, 25 000, and 12×10−6 for the 2% Nb alloy, and 0.85 T, 1.5 A/m 17 400, and 14×10−6 for the 8% Ta alloy. The Curie temperature is 531 K for the 2% Nb alloy and 538 K for the 8% Ta alloy. The success in synthesizing the new amorphous alloys with the wide supercooled liquid region and good soft magnetic properties is promising for future development as soft magnetic bulk amorphous alloys.

Soft Magnetic Properties of Co-Based Amorphous Alloys with Wide Supercooled Liquid Region

New Co-based amorphous alloys with a wide supercooled liquid region above 40 K before crystallization and good soft magnetic properties were synthesized in the Co 72-x Fe x Zr 8 B 20 and Co 63 Fe 7 Zr 10-x M x B 20 (M=Nb, Ta or W) systems. The supercooled liquid region defined by the difference between crystallization temperature (T x ) and glass transition temperature (T g ), ΔT x (=T x -T g ), is 39 K for Co 56 Fe 16 Zr 8 B 20 , 45 K for Co 63 Fe 7 Zr 6 Nb 4 B 20 , 40 K for Co 63 Fe 7 Zr 4 Ta 6 B 20 and 44 K for Co 63 Fe 7 Zr 6 W 4 B 20 . The glass transition is also observed for the Co 63 Fe 7 M 10 B 20 (M=Ta or W) alloys. The Co-based amorphous alloys with ΔT x above 40K exhibit low coercivity of 2.5 to 5.6 A/m, low magnetostriction of 1.7 x 10 -6 to 3.0 x 10 -6 and high permeability (μ e ) of 10000 to 23000 at 1 kHz. The good μ e characteristics are maintained in a high frequency range and the μ e at 1 MHz is 5700 for Co 56 Fe 16 Zr 8 B 20 and 6800 for Co 63 Fe 7 Zr 6 Ta 4 B 20 . The high frequency permeability is superior to those for conventional Co- and Fe-based amorphous alloys. The electrical resistivity (ρ n ) is as high as 1.7 to 2.0 μΩm and hence the reduction of eddy current loss caused by the high ρ n is presumed to be the origin of the better high-frequency permeability. The simultaneous achievements of good soft magnetic properties and high ρ n are presumably due to the formation of a unique amorphous structure in which two kinds of atomic pairs of metal-metal (Co-Fe-Zr-M) and metal-metalloid (Co-Fe-Zr-M-B) types are homogeneously mixed on a subnanoscale, because the former type pair has good soft magnetic properties and the latter type pair has high ρ n The good combination of high stability of the supercooled liquid and good soft magnetic properties is expected to induce future development as a new type of soft magnetic bulk amorphous alloy.

Heat Treatment of Molten Rapidly Quenched Precursor as a Method to Improve the Glass Forming Ability of Alloys

AbstractImprovement of glass forming ability (GFA) of two soft magnetic amorphous alloys (Fe75.5Ni1 3Si8.6B13.5 and Co69.6Fe1.3Mn4.5Si14.3B9 3Mo1) by heat treatment of melts prepared from different precursors (bulk ingot, rapidly quenched ribbons and granules) was studied. An assumption that the maximum undercooling ability corresponds to the maximum GFA was used to optimize the heat treatment mode. A temperature range was found by DTA for each alloy melt, favoring its undercooling (so called “undercoolable melt”). Usage of rapidly quenched precursor expands the range towards lower temperatures. GFA of the alloys was estimated by several melt quench techniques (casting, spinning and INROWASP). Fully amorphous samples with the thickness of 0.06–0.5 mm were prepared.

Nanocrystallization and magnetic properties of Fe 56Co 7Ni 7Zr 2M 8B 20(M = Nb or Ta) Glassy alloys

Glassy alloys with a wide supercooled liquid region before crystallization were found in melt-spun Fe 56Co 7Ni 7Zr 2M 8B 20 (M = Nb or Ta) alloys. The temperature interval of the supercooled liquid region defined by the difference between glass transition temperature (T g) and crystallization temperature (T x), ΔT x(=T x-T g) is about 60 K for these alloys. The crystallization occurs through distinct two stages. The crystallization behavior seems to reflect the existence of Fe 2(M,Zr) phase resulting from the weaker bonding nature of Fe-M pair as compared with Fe-Zr pair. Good soft magnetic properties are obtained in the annealed state for 300s at 800K below T g for these alloys. Saturation magnetization (I s), coercive force (H c) and effective permeability ( μ e ) at 1 kHz are about 0.8T, 2A/m and 18000, respectively. The above-mentioned glassy alloys with wide supercooled liquid region and good soft magnetic properties have a strong possibility of producing soft magnetic bulk amorphous alloys.

Thermodynamics of amorphous magnets with ferromagnetic and antiferromagnetic coupling

Two-component amorphous magnetic alloys are considered, with ferromagnetic coupling between atoms of the same subsystem, but antiferromagnetic coupling between atoms belonging to different subsystems. It is shown that in such systems a complete magnetic moment compensation at finite temperatures is impossible, except globally at certain compensation points. As a consequence, a crystalline antiferromagnetic alloy generically alloy generically goes ferrimagnetic upon amorphization. The qualitative behaviour of the averaged spontaneous magnetization is investigated throughout the entire temperature range, in a mean-field approximation near the critical temperature, and in a random-phase approximation at low temperatures. The structural properties of the system are taken into account through certain correlation functions of the positions of the atoms. It is shown that in a magnetic alloy the temperature dependence of the magnetic moment depends essentially on the concentration of the components, and on certain effective exchange parameters. Depending on these parameters, there can be 0, 1 or 2 compensation points, and the concentration-dependence of the ordering temperature Θ N can be linear, concave, convex or “mixed concave-convex”.

Giant magneto-impedance effects in nanocrystalline soft magnetic alloy ribbons

SINCE the discovery of the giant magneto-impedance (GMI) effects in amorphous wire (or rib-bon) of CoFeSiB and nanocrystalline wire (or film) of FeCuNbSiB, it has attracted greatattention due to its promising potential applications in industry. Amorphous (and nanocrys-talline) soft magnetic alloys have very large magnetic permeability, when an ac driving currentand an external magnetic field (EMF) are applied, the EMF will damp the magnetic fluxchange caused by the ac driving current, thus the magnetic permeability will decrease; as a re-...

The spin-dependent electronic structure of amorphous magnetic alloys

Spin-resolved photoemission from FeB and CoB binary amorphous alloys has been measured using, for the first time, a synchrotron radiation source. A comparison of the experimental results with several ab initio calculations on two model systems Fe80B20 and Co77B23 shows that the spin-resolved photoemission provided a critical test of theoretical models, and gives insight into the spin-dependent electronic structures of these materials.

Magnetoelastic sensors based on soft amorphous magnetic alloys

Magnetoelastic properties of soft amorphous magnetostrictive alloys are used in high efficiency sensors: when negative magnetostriction (Co-rich) samples are used, a stress sensor can be easily constructed by using the continuous and linear increase of the magnetoelastic anisotropy induced by the applied stress. In this work we report on one of these sensors with a figure of merit of 104 and a range of utilization that extends almost to the theoretical elastic limit of the sample. On the other hand, high positive magnetostriction (Fe-rich) metallic glasses are characterized by the frequency of the longitudinal vibrational mode of the samples, ωr being a function of the applied static field H. Studies performed about the performance of ωr as a carrier of information (i.e., object recognizer) are discussed, and a new sample configuration for this purpose is presented.