Akinori Kojima

Compositional dependence of the soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys with high magnetic flux density

The compositional dependence of the soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys has been investigated. The magnetostriction (λs) and the grain size of the (Fe90Zr7B3)1−x(Fe84Nb7B9)x alloys, which are two typical ternary alloys mixed with the best soft magnetic properties, show intermediate values between those of the Fe90Zr7B3 with negative λs and the Fe84Nb7B9 with positive λs. However, the soft magnetic properties of the Fe–(Zr,u200aNb)7–B alloys are inferior to those of the Fe90Zr7B3 and the Fe84Nb7B9 alloys. The best soft magnetic properties have been obtained at Zr+Nb=6u200aat.u200a%. The Fe85.5Zr2Nb4B8.5 alloy shows a high μe of 60u2009000 at 1 kHz, a high Bs of 1.64 T, and zero λs, simultaneously. The alloy also exhibits a very low core loss of 0.09 W/kg at 1.4 T and 50 Hz, which is extremely lower than that of Fe–Si–B amorphous alloys. The nanocrystalline Fe–Zr–Nb–B alloys with improved soft magnetic properties are therefore suitable for pole transformers.

Rapid-annealing effect on the microstructure and magnetic properties of the Fe-rich nanocomposite magnets

The rapid-annealing effect on the microstructure and magnetic properties of the nanocomposite Fe93-x-yCoxNb2(Nd,u200aPr)yB5 (x=0–20, y=5–7 at.u200a%) alloys produced by crystallization of an amorphous phase have been investigated. The melt-spun ribbons consist of an amorphous phase in the as-quenched state and the amorphous phase changes to a nanocomposite structure consisting mainly of bcc-(Fe, Co), (Nd,u200aPr)2(Fe,u200aCo)14B and residual amorphous phases after annealing at temperatures of 973–1023 K. The nanocomposite alloys exhibit improved values of remanence (Jr), coercive force (HcJ), and maximum energy product [(BH)max] upon annealing at a higher heating rate (α) in the temperature range corresponding to the primary crystallization temperature of bcc-Fe phase. As α increases, the grain sizes of each phase decrease, especially for the Nd2Fe14B phase, and the ratio of total surface area of the Nd2Fe14B to bcc-Fe phases (Shard/Ssoft), which are evaluated assuming each grain is a sphere, becomes close to 1 for the F...

Magnetic properties of zero-magnetostrictive nanocrystalline Fe}Zr}Nb}B soft magnetic alloys with high magnetic induction

Abstract The soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys have been investigated. The best soft magnetic properties have been obtained for the Fe85.5Zr2Nb4B8.5 alloy. The alloy shows a high permeability of 60,000 at 1xa0kHz, a high magnetic induction of 1.64xa0T and zero magnetostriction, simultaneously. The alloy also exhibits a very low core loss of 0.09xa0W/kg at 1.4xa0T and 50xa0Hz, which is extremely lower than that of Fe–Si–B amorphous. The nanocrystalline Fe–Zr–Nb–B alloy is therefore suitable for a core material for pole transformers.

Low core losses of nanocrystalline Fe–Zr–Nb–B soft magnetic alloys with high magnetic flux density

Abstract The soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys, which are mixed Fe–Zr–B alloy with negative magnetostriction and Fe–Nb–B alloy with positive one, have been investigated. The magnetostriction and the grain size of the Fe–Zr–Nb–B alloys show intermediate values between those of the Fe–Zr–B and Fe–Nb–B alloys. The soft magnetic properties are strongly affected by Zr+Nb amount and Zr/Nb ratio. The best soft magnetic properties have been obtained for the Fe85.5Zr2Nb4B8.5 alloy. The alloy shows a high permeability of 60xa0000 at 1xa0kHz, a high saturation magnetic flux density of 1.64xa0T and zero-magnetostriction, simultaneously. The alloy also exhibits a very low core loss of 0.09xa0W/kg at 1.4xa0T and 50xa0Hz, which is extremely lower than that of Fe–Si–B amorphous, and good thermal stability of the core loss. The nanocrystalline Fe–Zr–Nb–B alloy is therefore suitable for a core material for pole transformers.

Micro structure of nanocrystalline Fe-Nb-Pr-B alloys produced by crystallization of amorphous phase

Abstract The crystallization behavior and magnetic properties of the melt-spun amorphous Fe88Pr7B5, Fe88Nb2Pr5B5 and Fe86Nb2Pr7B5 alloys were investigated. These alloys have a nanocrystalline structure consisting of bcc-Fe, Fe14Pr2B and remaining amorphous phases and exhibit rather good hard magnetic properties, Hc of 210–270 kA m−1, Ir of 0.93–1.23 T, after annealing for 180 s at 923–1023 K. The Fe88Nb2Pr5B5 alloy exhibits the highest (BH)max of 110 kJ m−3 among the three alloys and has the fine nanocrystalline mixed structure with grain sizes of 10–20 nm. The fine grain size is presumably due to the high thermal stability of the remaining amorphous phase with enriched Nb concentrations.

Effect of Co addition on the magnetic properties of nanocrystalline Fe-rich Fe-Nb-(Nd,Pr)-B alloys produced by crystallization of an amorphous phase

The effect of Co addition on the magnetic properties and microstructure for the nanocrystalline Fe93-xNb2(Nd,Pr)2B2 (x = 5–7) alloys produced by crystallization of an amorphous phase has been investigated. The melt-spun Fe93-x-yCoxNb2(Nd,Pr)yB5 (x = 0–20 and y = 5–7 at.%) ribbons form a nanocomposite structure of bcc-(Fe,Co) and Pr2(Fe,Co)14B with grain sizes of 10–50 nm after annealing at 973-1023 K, showing a smooth J-H curve typical for the exchange-spring magnet. The alloys containing Co show a high energy product ((BH)max) upon annealing at a relatively low temperature presumably because the precipitation temperature of each phase decreases by addition of CO. The (BH)max values after annealing at an optimum temperature are improved by addition of 5–20 at. % Co for the Fe86-xCoxNb2(Nd,Pr)7B5 and Fe88-xCoxNb2Nd5B5 alloys. The improvement of (BH)max by Co addition is attributed to the enhancement of Jr, presumably resulting from the increase in magnetization of each phase and the exchange-coupled region between the soft and hard magnetic phases.

Effect of Nd substitution on the soft magnetic properties of a nanocrystalline Fe84Nb7B9 Alloy

Abstract The substitution effect of Nd for Nb on the structure and magnetic properties of a Fe 84 Nb 7 B 9 alloy has been investigated. The substitution of Nd causes the formation of Fe 3 B phase in the as-quenched state; Decrease the crystallization temperature and increase the Curie temperature of the amorphous phase. After annealing at an optimum temperature; The soft magnetic properties are improved by substitution of 0.05 to 0.4 at% Nd and Fe 84 Nb 6.9 Nd 0.1 B 9 alloy exhibits the permeability (μ′) at 1kHz of 39000 and the coercivity (H c ) of 4.3 A/m.