Ryusuke Hasegawa

Iron‐boron metallic glasses

By rapid quenching from the liquid, binary Fe100−xBx glasses are produced over the range 12–28 at.% B. Magnetization measurements in these glasses indicate a compositional dependence of the saturation magnetic moment μs which is consistent with the compositional dependence of the density of the material and reflects electron charge transfer from boron to iron. The extrapolated value of μs for noncrystalline Fe metal is found to be close to that for pure crystalline iron (μs=2.2μB); this is lower than the value of 2.4μB previously estimated for amorphous Fe. Based on x‐ray and thermomagnetization data, it is argued that the local atomic arrangements resemble those of bcc iron for the Fe‐rich alloys (x<16 at.%) and are similar to those of orthorhombic Fe3B in the vicinity of x=20. For x≳25, the local atomic structure seems like that of tetragonal Fe2B. These structural changes can explain the unexpected decrease of the Curie temperature with decreasing boron content. The decrease of the crystallization temp...

Amorphous magnetism--II

Survey of Theories of Spin Glass.- Some Percolation Scaling Applications to Low Temperature Dilute Magnets.- + Studies of Dilute PdFe Alloys.- Spin Waves in Heisehberg Spin Glasses.- Temperature-Dependent Skew Scattering in an AuMn Spin Glass.- Slowly Relaxing Remanence and Metastability of Spin Glasses.- Effective Field Theories of Topologically Disordered Magnets.- Spin Glasses and Mictomagnets - Revisited.- Concentration Effects in Spin Glasses.- Effect of Pressure on Impurity-Impurity Interactions in Spin Glass Alloys.- Critical Properties of a Simple Glass Model.- Magnetic Ordering of AuCr: An Ultrasonic Investigation.- Two Approaches to the Theory of Spin Glasses: A Comparison with Each Other and with Experiment.- Localized Moment and Spin-Glass-Like Behavior in Amorphous YFe2.- Real Space Renormalization Group Calculations for Spin Glasses.- The Remanent Magnetization of Spin Glasses and the Dipolar Coupling.- The Magnetic Behavior of Pd-Mn Alloys.- Some Controversial Aspects of Electronic and Magnetic Interactions in the Amorphous Metallic State.- Magnetic Susceptibility of an Amorphous Non-Transition Metal Alloy: Mg 70Zn 30.- 31P Nuclear Magnetic Resonance Study in the Metallic Glass Systems (Niy Pt1?y), 75P25 and (Ni0.50Pd0.50)100?xPx.- NMR and Mossbauer Studies of the Amorphous System Fe79P21?xBx+.- Magnetism in Amorphous Zr-Cu(Fe), Zr-Cu(Gd), and Nb-Ni(Fe).- From Superconductivity to Ferromagnetism in Amorphous Gd-La-Au Alloys.- The High Temperature Electronic and Magnetic Properties of Pd-Alloys in the Glassy, Crystalline and Liquid State.- Ferromagnetic and Antiferromagnetic Coupling in Amorphous (Ni100-cMnc)78P14B8.- Electronic and Magnetic Properties of Amorphous Fe-P-B Alloys.- Mossbauer Study of a Glassy Fe80B20 Ferromagnet.- The Resistivity of Amorphous Ferromagnets.- Magnetic Regimes in Amorphous Ni-Fe-P-B Alloys.- Resistivity of Metglas Alloys From 1.5 K to 800 K.- Electrical Resistivity and Crystallization of Amorphous Metglas 2826 and Metglas 2826A.- Transformation of Some Amorphous FePC Alloys During Isothermal Aging.- Perspective on Application of Amorphous Alloys in Magnetic Devices.- High Magnetic Permeability Amorphous Alloys of the Fe-Ni-Si-B System.- Magnetostriction of Metallic Glasses.- On the Magnetically Induced Anisotropy in Amorphous Ferromagnetic Alloys.- Application of Domain Wall Pinning Theory to Amorphous Ferromagnetic Materials.- Magnetic Characterization of Semi-Amorphous Nickel on Alumina Dispersions: Correlations with Their Methanation and Chemisorption Activities.- Surface Effects in Amorphous Ferromagnets with Random Anisotropy.- Spin Wave Excitation and Propagation in Amorphous Bubble Films.- Temperature Dependence of the Extraordinary Hall Effect in Amorphous Co-Gd-Mo Thin Films.- Current Views on the Structure of Amorphous Metals II.- Structure Simulation of Transition Metal - Metalloid Glasses, II.- Structural Models for Amorphous Transition Metal Binary Alloys.- Small-Angle Magnetic Scattering in Amorphous TbFe2.- Magnetism and Structure of Amorphous Fe80P13C7 Alloy.- The Magnetic and Electronic Properties of Amorphous Nickel Phosphorus Alloys.- Structure and Physical Properties of an Amorphous Cu57Zr43 Alloy.- A Proposed Structure Model for Amorphous Pd0.8Si0.2 Alloy.- Ground State of an Ising Antiferromagnet with a Dense Random Packing Structure.- Magnetic Resonance and Glass Structure.- Magnetic Susceptibility and EPR Studies of Reduced Titanium Phosphate Glass.- Characterization of Ferromagnetic Precipitates in Glass by Ferromagnetic Resonance.- Low Temperature Thermal Conductivity of MnO*Al2O3*SiO2 Glass.- A Calorimetric Investigation of a CoO*Al2O3*SiO2.- Exchange Fields and Crystal Fields in CoO*Al2O3*SiO2 Glass: A Mossbauer Study.- Oxidation - Reduction Equilibrium in Glass Forming Melts.- Effect of Temperature and Oxygen Partial Pressure on Coordination and Valence States of Fe Cations in Calcium Silicate Glasses - A Mossbauer Study.- A Mossbauer Study on the Clustering and Crystallization Phenomena in BaO-4B2O3 Glasses Containing Dilute Concentrations of Fe2O3.- Magnetic Properties of (Fe2O3-TiO2) in BaO-B2O3-SiO2 Oxide Glasses.- Magnetic Properties of an Iron Borosilicate Glass.- Paramagnetic Impurity Concentrations in Amorphous Polymers.- List of Participants.

Present status of amorphous soft magnetic alloys

Application of amorphous soft magnets in electric-utility and industrial transformers are increasingly being adopted, helping to solve global warming and energy-saving problems. In addition, amorphous metal-based magnetic components are used in power electronics, telecommunication equipment, sensing devices, electronic article surveillance systems, etc. Some magnetic inductors find applications in pulse power devices, automotive ignition coils, and electric power conditioning systems. All of these applications are possible because of faster flux reversal, lower magnetic loss and more versatile property modification achievable in amorphous alloys. Improvements in materials processing and device fabrication technology will continue to take place, which will further increase the universe of application of amorphous soft magnets. Some fundamental problems associated with the applications are mentioned.

Static bubble domain properties of amorphous Gd–Co films

Metallic Gd1−xCox films (0.75 < × <0.85) obtained in the amorphous state by an rf‐sputtering were investigated using the Kerr polar magneto‐optic effect. These films exhibit perpendicular anisotropy sufficient to sustain magnetic cylindrical domains. The magnetic properties obtained with a Kerr hysteresigraph from these films can be described in terms of the wall energy model developed originally for nonmetallic single‐crystal bubble material. An analysis based on a simple molecular field description of the magnetization and a mean field approximation of the exchange constant A gives estimates of the uniaxial anisotropy energy Ku. The results indicate that for the composition range studied A increases linearly from 5.7 to 6.6 (10−7 erg/cm), while Ku ranges between 1 and 7 (105 erg/cm3). The saturation magnetization Ms varies between 30 and 180 G. The moderate anisotropy (Q=Ku/2πMs2 = 1–9) and low wall motion coercivity of less than 1 Oe are favorable to bubble device applications. The effect of thermal an...

Applications of amorphous magnetic alloys in electronic devices

Abstract Some of the features of amorphous magnetic alloys that differentiate them from other soft magnetic materials include: low magnetic loss, fast flux reversal, high electrical resistivity and low acoustic loss. Furthermore, a wide range of B–H characteristics can be obtained through alloy design and heat-treatment of the alloys under different conditions. The versatile properties thus obtained can then be utilized in a number of magnetic applications ranging from large electrical power devices such as transformers and motors to recording heads and to anti-pilferage markers. This paper reviews the applications of various amorphous magnetic alloys in electronic devices including magnetic components in power electronics, telecommunication equipment, automotive parts and sensing devices. Relationships between property requirements and material capabilities are also discussed.

Temperature and compositional dependence of magnetic bubble properties of amorphous Gd‐Co‐Mo films

It is shown that the temperature and compositional dependence of the magnetic bubble properties of amorphous Gd‐Co‐Mo sputtered films can be described satisfactorily by simple models based on mean field analysis of the experimental data. Using the fitting parameters obtained, bubble properties such as 4πMs, l, Q, and Hs (collapse field) are predicted as a function of temeprature for 1‐, 0.5‐, and 0.25‐μm‐diam bubbles. Optimum compositions for small temperature derivatives are suggested by this analysis. Some consideration of the dynamic properties for the present ternary films is also given.

Effect of thermal annealing and ion radiation on the coercivity of amorphous Gd–Co films

Ferrimagnetic amorphous Gd–Co films deposited by rf sputtering with uniaxial perpendicular anisotropy were annealed at about 200 °C with or without a magnetic field of 3 kOe applied perpendicularly to the film plane. Data taken using the polar Kerr magneto‐optic effect show a significant decrease in the value of the wall‐motion coercivity Hc. A reduction of Hc by an order of magnitude was generally attained in films having compositions in the vicinity of the magnetic compensation point. Similar results were obtained in a film irradiated with 2.5‐MeV argon ions. These data are discussed in terms of fluctuations in various parameters contributing to the resultant coercivity. The results indicate that the fluctuations in the exchange stiffness constant dominate over the others and, consequently, are most affected by the postdeposition treatments. The results for the ion‐irradiated film suggest that the origin of the uniaxial anisotropy is due to pair ordering of Co atoms.

Low‐field magnetic properties of Fe80B20 glass

The low‐field magnetic properties of Fe80B20 glass are examined. Measurements are reported for straight strips, stressed and unstressed, for as‐cast/as‐wound toroids and for field‐annealed toroids. Due to the positive magnetostriction (λs=31×10−6) of the alloy, the low‐field magnetic properties of strips are improved by applied tensile stress. Similarly, toroids annealed to remove compressive stresses induced by winding (cooled in a magnetic field) are superior to unannealed toroids. Field‐annealed Fe80B20 toroids show a coercivity of ∼0.04 Oe, a permeability of 4000 at 20 G, and a remanence ratio of 0.77Bs(Bs=16 kG). The approach of the magnetization to saturation for field‐annealed toroids indicates a magnetic anisotropy energy density of about 5×103 erg/cm3. This low magnetic anisotropy, as well as the low coercivity and high resistivity (145 μΩ cm±10%) exhibited by Fe80B20 lead to low core loss under ac excitation, i.e., 0.10 W/kg (measured at 1 kHz and a maximum induction of 1 kG on a field‐annealed ...

Amorphous alloy core distribution transformers

The authors present a summary of activities in the development of amorphous metals, the development of amorphous core distribution transformer, and the future potential of amorphous materials and transformers. Amorphous metals possess unique properties. Made by rapid quenching of liquid metal, the metal has atoms arranged in a random fashion, making the material easy to magnetize. Transformers made using amorphous materials for cores exhibit losses that are 60%-70% less than comparable transformers made with silicon iron cores. The application of amorphous alloys in transformer designs is described, highlighting some theoretical points about the material as well as practical information about transformer design. >

Soft magnetic properties of metallic glasses—recent developments

Two major aspects of the soft magnetic properties of metallic glasses, i.e., high magnetic permeability and high saturation induction, are discussed. Recent development in the area of high permeability materials is centered around the zero‐magnetostriction Co‐rich metallic glasses having Si and B as metalloids. The heat treated materials studied thus far show low‐field magnetic properties comparable or superior to those of commercial supermalloy. A typical example includes an effective permeability at l kHz exceeding 50,000. Attractive high saturation induction metallic glasses are found in the series Fe82B18−xSix. Typical dc results for field‐annealed samples of this glass with x=8 are Hc=0.03 Oe, Br=12 kG and μ (20) =8,000. Core loss under sine flux conditions at 60 Hz is 0.24 watts/kg at 16 kG. This value is nearly five times lower than that of the widely used power transformer material grade M‐4 Si/Fe (1.3 watts/kg) and well below that of Fe‐B glass. The stability against crystallization of Fe82B10Si8...