Takao Sawa

Effect of large boron additions to magnetically hard Fe-Pt alloys

Magnetic properties were investigated for the ternary (Fe0.6Pt0.4)100−xBx and (Fe1−yPty)83B17 alloy ribbons prepared by the twin roll technique. Boron changes the compositions of the ordered FePt (γ1) phase, which coexists with Fe2B at various alloy compositions so that the actual Pt content of γ1 in the ternary alloy goes up with increasing boron content. Coercive force increase due to boron addition is remarkable, in particular at low Pt concentration. Annealing time to get high coercivity becomes much shorter by boron addition. iHc=5.6 kOe and 4πMs=7.8 kG were obtained in the (Fe0.65Pt0.35)83B17 ribbon.

Magnetic properties of FeCu (3d transition metals) SiB alloys with fine grain structure

Soft magnetic properties were investigated together with crystallization process and grain size for FeCu (3d transition metals) SiB alloys with fine grains. They were rapidly quenched from the melt to achieve amorphous states and then annealed above their crystallization temperatures. In the group of 3d transition metals studied, low magnetic core loss at high frequency was obtained for V‐substituted Fe‐based alloys, because only a bcc Fe solid solution with diameter of about 20 nm precipitated. On the other hand, Cr‐ or Mn‐substituted alloys could not be attained with good soft magnetic properties because of the existence of Fe‐metalloid compounds besides the bcc phase by annealing above their crystallization temperatures. The effect of grain size on the soft magnetic properties is more prominent at lower frequency. Diffraction peaks which are characteristics of an ordered phase (DO3) are observed, which is the origin of excellent soft magnetic properties in FeAlSi alloys.

Magnetostriction and magnetic core loss at high frequency in amorphous Fe‐Nb‐Si‐B alloys

Magnetostriction and magnetic core loss at high frequency up to 100 kHz were investigated together with crystallization temperature, saturation magnetization, and magnetic permeability for amorphous (Fe1−xNbx)zSi88−zB12 alloys. Crystallization temperature significantly rises with Nb addition, particularly in the high z region. Magnetostriction decreases with increasing Nb content and z value. Magnetic core loss decreases and magnetic permeability increases with decreasing magnetostriction. Magnetic core loss reduction due to Nb addition were analyzed to be mainly attributed to domain width reduction through the decrease of magnetostriction.

Soft magnetic properties of ultrathin Co-based amorphous alloy ribbons with thickness of 3-10 /spl mu/m

Ultrathin zero-magnetostrictive amorphous ((Fe/sub 0.05/Co/sub 0.95/)/sub 0.95/ Cr/sub 0.05/)/sub 75/(Si/sub 0.5/B/sub 0.5/)/sub 25/ ribbons with thickness of 3-10 mu m were fabricated by a single roller quenching method in vacuum. The ribbons obtained had a good smooth surface and dimensional uniformity. The core loss of toroidal samples 10 mm in diameter was measured after annealing and found to decrease with decreasing ribbon thickness. For 5.5- mu m-thick ribbons, the losses at 1 MHz and 10 MHz were 1.0 J/m/sup 3/ (=1.0 W/cm/sup 3/) and 8.8 J/m/sup 3/ (=88 W/cm/sup 3/) for B/sub m/=0.1 T, respectively. The former value was 2/5 that of Mn-Zn high-frequency ferrites and 1/3 that of 5- mu m Supermalloy tape wound cores. Furthermore, extremely low losses were obtained for 3.8- mu m-thick ribbon at 2-10 MHz. In addition, remarkably high initial permeability beyond 100 kHz was also attained. The values of 5.5- mu m-thick ribbons measured at 1 and 10 MHz were about 10000 and 1200 for H/sub m/=2 mOe, respectively. >

Very low loss ultrathin Co-based amorphous ribbon cores

Ultrathin Co‐based amorphous ribbons with a thickness of 6–10 μm were fabricated by a single roller quenching method in vacuum. The compositions of the alloys were zero magnetostrictive: Fe4.7Co70.3Si15B10 and (Fe0.05Co0.95)71(Si0.5B0.5)29. The ribbons obtained had good smoothness and dimensional uniformity. The core loss of toroidal samples 15 mm in diameter was measured after annealing. The loss decreased with decreasing ribbon thickness. In the case of 6.4‐μm‐thick (Fe,Co)71(Si,B)29 amorphous ribbon, the values at 100 kHz and 1 MHz were 40 mW/cm3 and 1.8 W/cm3 for Bm=0.1 T, respectively. The former was 1/4 that of Mn‐Zn ferrites or 1/2 that of 5‐μm‐thick Supermalloy tape wound core loss. The latter was (2)/(3) that of 5‐μm Supermalloy tape wound core loss. In addition, the initial permeability beyond 100 kHz was also markedly improved by thickness reduction. The values of 6.4‐μm‐thick (Fe,Co)71(Si,B)29 ribbon measured at 1 and 10 MHz were about 7000 and 1000 for Hm=2 mOe, respectively.

Low magnetostrictive amorphous Fe‐Nb‐Si‐B alloys

Magnetostriction and magnetic core loss at high frequency up to 50 kHz were investigated together with saturation magnetization, Curie temperature, and crystallization temperature for amorphous (Fe1−xNbx)83Si5B12 alloys. Magnetostriction decreases with Nb content, and becomes 1×10−6 for x=0.115. Magnetostriction was shown not to be proportional to the square of saturation magnetization unlike many Fe‐based amorphous alloys. Iron loss at high frequency was measured on the core before and after resin molding. Iron loss increase due to resin molding was reduced as magnetostriction decreases. The incremental rate of the loss due to resin molding was increased as frequency decreases.

The frequency dependence of ac coercivity of ultrathin, low magnetostriction Co‐based amorphous ribbons

The dynamic (ac) coercivity of zero magnetostriction Co‐based ultrathin amorphous ribbons from the [(Co0.95Fe0.05)0.95Cr0.05]75Si15B10 family was measured over the frequency range of 20 Hz to 20 kHz. Ribbons with thicknesses between 5.3 and 18 μm, and widths held constant at approximately 6 mm, were studied. The results are well fit by a power law dependence of the coercivity Hc on frequency f. The exponent which characterizes the best fit to the data depends on ribbon thickness. Within experimental uncertainty, the exponent increases linearly with ribbon thickness, varying between 0.18 and 0.32 for the ribbons studied. In contrast, simple phenomenological models predict a constant value of 0.5 for the exponent. The origins of the deviations from this simple phenomenological dependence of coercivity on frequency are discussed.

Magnetic properties and microstructure of rapidly quenched SmZrFeCoN magnets

Dependence of magnetic properties and microstructure on boron additions for nitrogenated (Sm,Zr)(Fe,Co)/sub 9/ alloys fabricated by rapidly quenching was investigated. The condition for getting high (BH)/sub max/ with high /sub i/H/sub c/ is to produce an amorphous phase in the rapidly quenched sample because it leads to the precipitation of uniform and fine grains by the annealing above their crystallization temperature. The role of boron is to form the amorphous phase easily by rapidly quenching. High (BH)/sub max/ of about 20 MGOe with high /sub i/H/sub c/ of 9.6 kOe was obtained for nitrogenated (Sm/sub 0.7/Zr/sub 0.3/)(Fe/sub 0.95/Co/sub 0.05/)/sub 9/B/sub 0.1/. High (BH)/sub max/ of 13.0 MGOe was also attained as an isotropic resin bonded magnet with density of 6.2 g/cm/sup 3/.

Magnetostriction and related properties in amorphous Fe-Nb-Si-B alloys

Abstract A study was carried out to get Fe-based amorphous alloys with low magnetostriction. Magnetostriction (γ s ) was measured as functions of Nb and Fe content in Fe-Nb-Si-B amorphous alloys. It was found that Nb decreases γ s , particularly in Fe-rich region.

Soft magnetic properties of ultrathin Fe-based amorphous alloy cores

Abstract Soft magnetic properties up to the megahertz range were investigated for Fe(Cr,Nb)SiB amorphous alloys of thickness 6–18 μm prepared by a single-roll method in vacuum. A low magnetic core loss of 1.5–2.0 W cm−3 at 1 MHz and 1 kG was attained by annealing near their crystallization temperatures. The annealing leads to the precipitation of excess α-Fe particles, so the d.c. coercive force changes drastically over 1 Oe. The magnetomechanical resonance effect due to magnetostriction in the initial permeability decreases upon substitution of Fe by Cr or upon annealing at higher temperature.