Nanocrystallization of amorphous (Fe 1-x Co x ) 88 Zr 7 B 4 Cu 1 alloys and their soft magnetic properties
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Amorphous ribbons of (Fe1-xCox)88Zr7B4Cu1 (x 5 0.2, 0.35, 0.5, and 0.6) alloys were annealed to produce a nanocrystalline phase dispersed in the amorphous matrix. Precision lattice parameter calculation showed that composition of the nanocrystalline phase is Fe73Co27 for all the alloys irrespective of initial alloy composition. This result was well corroborated with the Mössbauer results. Saturation magnetization of annealed ribbons was almost same for all the alloys, however, coercivity increases with Co content.
I. INTRODUCTION
Fe-based alloys containing nanocrystalline phase embedded in an amorphous matrix have attracted considerable attention as soft magnetic materials after the invention of Fe-Si-B-Nb-Cu (FINEMET) alloys by Yoshizawa et al.1 Subsequently, other nanocrystalline materials such as Fe-Zr-B-Cu (NANOPERM)2 and Fe(Co)-Zr-B-Cu (HITPERM)3 alloys with a variety of soft magnetic properties have been developed. Though Fe-Si-B-Nb-Cu and Fe-Zr-B-Cu alloys possess low coercivity, core loss, and magnetostriction combined with high permeability and saturation induction, these alloys are not suitable for applications above 250 °C due to low Curie temperature (Tc) of the residual amorphous matrix.4 In case of Fe(Co)Zr-B-Cu alloy developed by McHenry et al., the permeability is low, however, the Tc and the saturation induction (Ms) are considerably high as compared to the other nanocrystalline soft magnetic materials.4–7 The structure and magnetic properties of nanocrystalline Fe(Co)-Zr-B-Cu alloys have been studied by various investigators. Willard et al.5 have studied the crystallization behavior of Fe44Co44Zr7B4Cu1 alloy using synchrotron x-ray diffraction (XRD) method and reported that the crystallites are ordered a9-Fe(Co) phase (B2 structure). Muller et al.8 have reported that at higher Co content, fcc Co phase precipitates along with a-Fe(Co) phase in Fe86-xCox Zr7B6Cu1 alloys; the Tc of the amorphous phase was also found to increase with Co content and beyond 20 at.% Co, it is higher than the crystallization temperature of a-Fe(Co) phase resulting in difficulties of measuring Tc. Recently, the present investigators9 have observed that in (Fe0.65Co0.35)88 Zr7B4Cu1 alloy, the structure of as-spun ribbons changes from fully amorphous to partially amorphous/nanocrystalline a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.166 J. Mater. Res., Vol. 26, No. 16, Aug 28, 2011
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to fully nanocrystalline (bcc a-Fe(Co) + Fe2Zr) on decreasing the wheel speed and deteriorates the soft magnetic properties drastically. In this article, the structure and soft magnetic properties of melt-spun Fe-Co-Zr-B-Cu alloys containing different Co contents are reported. II. EXPERIMENTAL PROCEDURE
Alloys with nominal compositions of (Fe1-xCox)88 Zr7B4Cu1 with x 5 0.2, 0.35, 0.5, and 0.6 have been prepared by melting Fe-Zr eutectic alloy along with high purity Fe, Co, B, and Cu in a vacuum induction furnace (at a vacuum o
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