I. K. Kang

Effects of Al on the magnetic properties of nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloys

The effects of Al on the soft magnetic properties of nanocrystalline Fe73.5−xAlxCu1Nb3Si13.5B9 alloy ribbons are investigated in the composition range of 0≤x≤1.0. The relative initial permeability at 1 kHz is found to increase by the addition of Al, and reaches the peak value at x=0.1. The coercivity decreases, rather significantly, with the Al content in the whole composition range investigated in the present work, the values of the coercivity being 12.5 mOe at x=0 and 9.3 mOe at x=1.0. The magnetic induction at an applied field of 10 Oe, however, decreases moderately by the introduction of Al, possibly due to the dilution effect. The improvement in the soft magnetic properties is considered to result from the reduction in the grain size of the α Fe‐Si solid solution phase of the Al‐added alloy ribbons, which has been observed by transmission electron microscopy. Another factor may be due to the decrease in the intrinsic magnetocrystalline anisotropy K1 as Al is added to the alloy.

Microstructural change upon annealing FeZrB alloys with different boron contents

To clarify the reason for the change in effective permeability with increasing boron content before and after crystallization, we investigated the microstructure of Fe93−xZr7Bx (x = 2, 4, 6, 8) alloys annealed for 1 h in the temperature range 350–600 °C, using transmission electron microscope. In low boron alloys (x = 2, 4), the amorphous phase showed indications of a typical interconnected pattern, exhibiting a spinodal-type decomposition. After crystallization, it changed to a mainly single b.c.c. structure with a homogeneous grain size distribution of about 20 nm, and the effective permeability had a high value of around 19000. In high boron alloys (x = 6, 8), the microstructure after crystallization showed an inhomogeneous grain size distribution, and a low effective permeability. These results may be the result of the different phase separation pattern in the amorphous state.

Magnetostriction of melt-spun Dy-Fe-B alloys

The magnetostriction of melt‐spun ribbons of Dyx(Fe1−yBy)1−x (x=0.2, 0.25, 0.3; 0≤y≤0.2) alloys is systematically investigated as a function of the wheel speed during melt quenching. As the wheel speed increases from 10 to 50 m/s, the magnetic softness improves with the wheel speed rather continuously for the alloys with the Dy content x=0.2 and 0.25 but it exhibits a maximum at the wheel speed of 30 or 40 m/s for the alloys with the highest B content (x=0.3). The softness also improves with the B content for a fixed wheel speed. Homogeneous and ultrafine grain structure is observed for the first time even in the as‐spun state when the ribbons of the alloy Dy0.3(Fe0.8B0.2)0.7 are fabricated at the wheel speed of 30 m/s. The ribbon having the ultrafine grain structure exhibits good magnetic softness together with a high strain.

Magnetic properties of Fe73.5Cu1Nb3(SixB1−x)22.5 (x=0.5–0.8) alloys with ultrafine grain structures

The metalloid effect on magnetic properties and microstructures of iron‐based alloys with ultrafine grain structures was investigated. For Fe73.5Cu1Nb3(SixB1−x)22.5 (0.5≤x≤0.8) alloys with 10–15‐nm grain diameters, the permeability increased with Si content. The alloys with x=0.5 and 0.6 subjected to the optimum heat treatment had two different ferromagnetic phases which were composed of an α‐Fe(Si) solid solution with high Curie temperature and an interfacial phase with low Curie temperature. However, in high Si alloys with x=0.7 and 0.8, only a phase with high Curie temperature appeared. This result suggests that in the high Si composition range, a complete transformation from the amorphous phase to the α‐Fe(Si) single phase was achieved. The disappearance of the interfacial phase which would certainly disturb the exchange coupling between the α‐Fe(Si) phase grains would be considered to be one of the factors for the increased permeability.

Low Temperature Magnetizaiton In Nanocrystalline Fe/sub 88/ Zr/sub 7/ B/sub 4/ Cu/sub 1/ Alloy

The authors report on the effect of annealing temperatures on the spin wave excitations for the nanocrystalline Fe/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/ alloy, observed from the low-temperature magnetization curve and the spectroscopic splitting g factor. The thermomagnetization curve at low temperature is found to obey the Bloch law, M/sub s/(T)=M/sub s/(0)(1-BT/sup 3/2/-CT/sup 5/2/). From these experimental results, spin wave stiffness constants within the annealing condition are calculated. The effective permeability, coercive force, saturation magnetization (B/sub 10/), magnetostriction and magnetic anisotropy of the annealed alloys are studied systematically. >

Soft magnetic properties of nanocrystalline Fe‐Hf‐C‐N films

Fe‐Hf‐C‐N films with excellent soft magnetic properties were fabricated by Ar+N2 reactive sputtering for the first time. The newly developed films were found to have better soft magnetic properties than those of Fe‐Hf‐C or Fe‐Hf‐N films. The best magnetic properties achieved in this work are  Hc of 0.15 Oe, μeff of 8200, and 4πMs of 17 kG. The thermal stability of the Fe‐Hf‐C‐N films was also found to be excellent, e.g., Hc was less than 0.3 Oe and μeff was about 4000 for the films annealed up to 700 °C. It was observed by transmission electron microscopy that the films consisted of two phases: a fine crystalline α‐Fe phase whose grain size is about 6 nm, and Hf(C,N) precipitates with a size of less than 2 nm. The fine grained α‐Fe structures, together with finely dispersed Hf(C,N) precipitates, is considered to be one of the main factors for the excellent magnetic properties and thermal stability.

Soft magnetic properties of Fe-B-M-Cu (M=Hf,Zr,Nb) alloys with nanocrystalline and amorphous hybrid structure

The change in magnetic properties with B content and annealing temperature was investigated for Fe-B-M-Cu (M=Hf,Zr,Nb) alloys. In the high B alloys over 8 at% B, the optimum annealing temperatures revealing the excellent soft magnetic properties were below the crystallization temperatures The annealed microstructure had ultrafine BCC-Fe phase grains with a diameter of 5-7 nm and a considerably high fraction (30-50 vol.%) of interfacial amorphous phase. For these alloys, very low core loss and high effective permeability were obtained in the frequency range up to 1 MHz. These behaviors were interpreted to be due their hybrid microstructure and high electrical resistivity. >

Influence of argon pressure on the composition of Co-early transition metal films fabricated by r.f. magnetron sputtering in the composite target mode

The effects of argon pressure and the solute element on compositional changes have been studied in binary Co-early transition metal (ETM) thin films fabricated by r.f. magnetron sputtering using the composite target mode. The solute concentration of the deposited film increases linearly with the area fraction of solute element of target and with the logarithm of argon pressure in the range 0.5–10 m torr. The compositional changes are discussed by considering not only the sputtering yield but also the argon pressure, which is related to the collision effect, and the difference in atomic weights between Co and ETM elements.

Effects of melt temperature on the magnetic properties of FeCuNbSiB alloy

The magnetic properties of an Fe73.5Cu1Nb3Si13.5B9 alloy with nanoscale crystalline structure have been investigated as a function of the melt temperature. In the temperature range of 1240 to 1380 °C investigated in the present study, the permeability increases with the melt temperature. This result may be explained in terms of the reduction in the magnetic anisotropy as a function of the melt temperature. This is supported by the results for the remanence ratio, which also increases with melt temperature in a similar manner to the permeability. In the latter part of the work described in this paper, the relationships between the permeability and the coercivity, and the permeability and the remanence ratio have been investigated for the nanocrystalline alloy. It was found that the permeability is correlated more closely to the remanence ratio than the coercivity.

Magnetic properties behaviors in Fe88Zr7B4Cu1 nanocrystalline alloy prepared by different postanneal cooling rates

Effects of cooling rate after annealing on the soft magnetic properties were investigated for an Fe88Zr7B4Cu1 alloy with nanoscale grain structure, which was prepared by melt quenching. As the cooling rate increased, the effective permeability improved and the remanence ratio, which indicates the orientation of magnetic anisotropy (degree of pair ordering), decreased. The increase of permeability and decrease of remanence ratio were considered to result from the suppression of the induced magnetic anisotropy. Furthermore, the variation of disaccommodation behaviors with cooling rate was investigated in the Fe88Zr7B4Cu1 nanocrystalline alloy. It was found that the value of D (intensity of disaccommodation) was a little higher for the samples obtained from the high cooling rate than that for the low cooling rate. This result can be explained by domain structure stabilization due to local induced magnetic anisotropy.