Kiyotaka Yamauchi

New Fe‐based soft magnetic alloys composed of ultrafine grain structure

Etude des relations entre proprietes magnetiques et compositions, conditions de recuit et microstructure des alliages Fe−Cu−Nb−Si−B

Magnetic properties of FeCuMSiB (M = Cr, V, Mo, Nb, Ta, W) alloys

Abstract Magnetic properties, microstructures and formed phases of nanocrystalline alloys prepared by annealing iron-based amorphous alloys added Cu and M (Cr, V, Mo, Nb, Ta, W) were investigated. Nb, No, Ta, W addition is very effective to improve soft magnetic properties. Especially, Nb is the most effective element to improve the soft magnetic properties. The order of the effect of decreasing the grain size is: Nb = Ta > Mo = W > V > Cr and is similar to that of the sofr magnetic properties.

Common mode choke cores using the new Fe‐based alloys composed of ultrafine grain structure

Common mode choke cores using the new Fe‐based alloys called ‘‘FINEMET’’ composed of ultrafine grain structure were developed. These new cores show high attenuation to high‐voltage pulse noises and good attenuation characteristics over a wide frequency range. Accordingly, the new cores are expected to be applied in many applications as line filters for electronic devices.

Effect of Additional Cu Element on Structure and Crystallization Behavior of Amorphous Fe-Nb-Si-B Alloys

The addition of Cu to an amorphous Fe74.5Nb3Si13.5B9 alloy was found to significantly change the crystallization process, resulting in the formation of a bcc solid solution containing a large amount of the solute elements with fine grains. It was further observed that the inhomogeneity of the amorphous structure increases upon the addition of Cu. The inhomogeneous amorphous structure was presumed to enhance the instability of the amorphous phase and the formation tendency of the bcc solid solution with soft magnetic properties.

Recent development of nanocrystalline soft magnetic alloys

Abstract Decreasing impurities and inclusions leading to the barrier of domain wall displacement and increasing the grain size are the classical leading principal for getting good soft magnetic properties. Hoffman theoretically revealed that the soft magnetic properties can be improved through the reduction of apparent magnetocrystalline anisotropy according to increasing of the inter-granular exchange interaction in magnetic thin films with nanocrystalline structure. We will describe the progress and background of typical nanocrystalline soft magnetic alloys concentrating on FeCuNbSiB originally found by the authors(1–2) and also FeMC(3), FeMB(4), FeMN(5) and FeMO (6)(M:Zr,Hf,Ta,Nb,etc. ), which show high saturation flux density and attractive soft magnetic properties.

A fluorescence X-ray absorption fine structure study of the effect of small amounts of additives on the formation of the nanocrystalline phase from metallic glass

Abstract Direct evidence that Nb and Cu atoms are associated with the nanocrystalline formation of Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3 was obtained using X-ray absorption fine structure (XAFS) measurements. XAFS results at the Cu K edge showed that the local structure around Cu atoms in Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3 changes from amorphous to f.c.c. prior to the precipitation of b.c.c. Fe(Si).The local structure around Nb atoms retains its amorphous state up to the second crystallization temperature and subsequently changes to the Fe 2 B crystalline state after being annealed at the second crystallization temperature.

Magnetic Properties of Nanocrystalline Fe-Based Soft Magnetic Alloys

Magnetic properties of nanocrystalline alloys produced by crystallization of Fe-Cu-Nb-Si-B amorphous alloys have been investigated. The best result is obtained at the annealing conditions where the main phase is bcc and it is very important to suppress the formation of Fe-B compounds with large magnetocrystalline anisotropy. Homogeneous and ultrafine grain structure has an important effect to improve the magnetic properties. Conclusively, soft magnetic properties of nanocrystalline alloys are related to various factors such as formed phases, ratio of amorphous phase, intrinsic magnetocrystalline anisotropy and magnetic interaction from grain boundary phase.

Properties of Ultrafine Crystalline (Fe-Cu 1 -Nb 3 )-Si-B Quasi-Ternary Alloys and Improvement of Their Magnetic Properties by Magnetic Field Annealing

The influence of the Si and B contents and of magnetic field annealing on the magnetic properties of ultrafine crystalline (Fe-Cu1-Nb3)-Si-B quasi-ternary alloys were studied. An alloy containing 13.5 at% Si and 9 at% B exhibited the best soft magnetic properties. The relative permeability of this alloy at 1 kHz is about 1 × 105. On the other hand, alloys containing about 2 at% Si and 13 at% B show a high flux density of about 1.55 T, and those containing about 17 at% Si and 5 at% B have nearly zero magnetostriction. Magnetic field annealing is very effective for improving the hysteresis curves of these alloys for many applications.

Displaced hysteresis loops of cobalt-based amorphous alloys

Abstract Asymmetrical displaced hysteresis loops of cobalt-based amorphous alloys sometimes appear when they are annealed in a magnetic field. The effect of composition and heat treatment conditions on asymmetrical displaced hysteresis loops of cobalt-based amorphous alloys were investigated in this study. As a result, the effect of composition, heat treatment conditions and the magnetic field on the hysteresis loops were clarified, although the cause of the phenomenon has not been resolved.

Magnetic properties of cobalt-rich amorphous alloys for saturable cores

Abstract The preferable properties for saturable cores used in magnetic amplifiers of high frequency switched-mode power supply are (1) a large remanence ratio Br/Bs, (2) a low core loss and (3) a small long-term change in the magnetic properties. In this paper, we discuss the fact that the controlled magnetization curve is preferable for evaluating saturable cores operating in magnetic amplifiers. The effect of induced magnetic anisotropy of cobalt-rich amorphous alloys on the magnetic properties is also discussed. Finally, we report a newly developed cobalt-rich amorphous alloy core, ACO-5SH, with superior magnetic properties for saturable cores.