Motoki Ohta

Magnetic properties of nanocrystalline Fe82.65Cu1.35SixB16−x alloys (x=0–7)

The Si content dependences of the magnetic properties of the Fe82.65Cu1.35SixB16−x alloys prepared by melt spinning were studied. The maximum Bs and minimum Hc were observed at around x=2 for the annealed Fe82.65Cu1.35SixB16−x alloys. The Bs and Hc of the annealed Fe82.65Cu1.35Si2B14 alloy were 1.84T and 6.5A∕m, respectively. The average grain size of the bcc Fe nanocrystal in the annealed alloys with x⩽2 was about 20nm, it increased with x at x>2. The annealing temperature range without the precipitation of o-Fe3B expanded with Si content.

New High-Bs Fe-Based Nanocrystalline Soft Magnetic Alloys

The magnetic properties and microstructures of newly developed Fe–Cu–B and Fe–Cu–Si–B alloys produced by melt-spinning have been studied. The annealed alloys consist of nanoscale grains. The annealed alloys show a high-saturation magnetic flux density Bs of more than 1.8 T and excellent soft magnetic properties such as a low core loss of about 0.3 W/kg at 50 Hz and 1.5 T (P15/50). For the present alloys, the addition of Cu is effective for the formation of nanoscale grains and the improvement of the soft magnetic properties.

Cu addition effect on soft magnetic properties in Fe–Si–B alloy system

The Cu content dependence of the magnetic properties in Fe84−xCuxSi2B14 and Fe82−xCuySi4B14 alloys prepared by melt spinning has been investigated. In the alloy with x=1.35, Bs increases and Hc decreases with annealing temperature TA up to 410°C, while in the alloys with x⩽1.0, Hc markedly increases at around TA=360°C. The values of Bs and Hc obtained in the annealed alloys are Bs⩽1.80T and Hc<7A∕m. With increasing Si content, the optimum Cu content for the appearance of excellent soft magnetic properties becomes higher and the optimum annealing temperature range expands.

Effect of Heating Rate on Soft Magnetic Properties in Nanocrystalline Fe80.5Cu1.5Si4B14 and Fe82Cu1Nb1Si4B12 Alloys

The effect of the heating rate in the annealing process of rapidly quenched Fe80.5Cu1.5Si4B14 and Fe82Cu1Nb1Si4B12 amorphous alloys on their soft magnetic properties is investigated. The iron loss in magnetic flux density region of B > 1.55 T in Fe80.5Cu1.5Si4B14 alloy decreases by high-heating-rate annealing (HA). The coercivity Hc and the saturation magnetic flux density Bs in HA specimen of Fe82Cu1Nb1Si4B12 alloy were about 3 A/m and 1.78 T. By applying HA to high-Fe-concentration amorphous alloys such as Fe82Cu1Nb1Si4B12, Fe82Cu1Nb1Si2B12P2, and Fe80.8Cu1.2Si5B11P2, the nanocrystalline alloys with a high Bs of more than 1.75 T and a low Hc of about 3 A/m are obtained.

Effect of Surface Microstructure on Magnetization Process in Fe

The magnetization processes of the Fe80.5Cu1.5Si4B14 nanocrystalline alloy were observed by Kerr effect. In the specimen annealed with heating rate of 0.3°C/s (NA), the pinning of domain walls was observed. Owing to such pinning effect in the NA specimen, high remanent magnetic flux density Br was obtained, and the hysteresis was observed in the B-H loop in the region of B > 1.5 T. Whereas, the smooth domain wall displacement was observed in the specimen annealed with the heating rate of 3°C/s (HA). The coarser grains near the surface observed in the NA specimen are considered to be the pinning site of the domain walls. In the HA specimen, grain growth in the heating process of annealing is suppressed.

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The relationship between the magnetic properties of a Co-based amorphous ribbon and its heating by a microwave magnetic field (hf) was investigated by using a 5.8-GHz single-mode applicator. The amorphous ribbon has a magnetic anisotropy in the ribbon plane. Heating efficiency of hf which was applied in the direction perpendicular to the casting direction was better than that of it applied along the casting direction. The contribution of magnetic loss to the hf heating was evaluated quantitatively when the hf was applied to both directions. The contribution of magnetic loss was more than 80% when the microwave hf was applied perpendicular to the casting direction, and less than 20% when it was applied parallel to the casting direction.