Magnetic Domain Structure of Nanocrystalline Zr 18-x Hf x Co 82 Ribbons: Effect of Hf
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Magnetic Domain Structure of Nanocrystalline Zr18-xHfxCo82 Ribbons: Effect of Hf Lanping Yue1, I. A. Al-Omari1,2,3, Wenyong Zhang1,2, Ralph Skomski1,2, and D. J. Sellmyer1, 2 1
Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588.
2
Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588. U.S.A.
3
Department of Physics, Sultan Qaboos University, PC 123, Muscat, Sultanate of Oman
ABSTRACT The effect of Hf on the permanent magnetism of nanocrystalline Zr18-xHfxCo82 ribbons (x = 0, 2, 4, and 6) was investigated by magnetic properties measurement and magnetic force microscopy (MFM). Emphasis is on the local magnetic domain structures in polycrystalline rapidly solidified Zr18-xHfxCo82 ribbons for four different samples with small fractions of Hf dopants (x ≤ 6). The investigation of the magnetic properties of the Zr18-xHfxCo82 ribbons revealed that all the samples under investigation are ferromagnetic at room temperature, and the corresponding MFM images show bright and dark contrast patterns with up-down magnetic domain structures. It is found that the saturation magnetization and the coercivity depend on Hf doping concentration x in the samples. For a sample with Hf concentration x = 4, the maximum energy product (BH)max value is 3.7 MGOe. The short magnetic correlation length of 131 nm and smallest root-mean-square phase shift value of 0.680 were observed for x = 4, which suggests the refinement of the magnetic domain structure due to weak intergranular exchange coupling in this sample. The above results indicate that suitable Hf addition is helpful for the magnetic domain structure refinement, the coecivity enhancement, and the energy-product improvement of this class of rare-earth-free nanocrystalline permanent-magnet materials. INTRODUCTION The limited resources and supplies of rare earths have led to a renewed interest in rareearth-free magnetic materials [1], and our research [2-4] is a part of this trend. Among the considered materials are Zr2Co11-based rare-earth-free permanent-magnet alloys. The additional elements (such as Mo, B, Al, Fe, Ni, etc.) added to Zr-Co alloys have been used to optimize the structures and improve magnetic properties [4-10]. We have recently reported that there are positive effects of substituting Zr by limited amounts of Hf on the coerecivity enhancement and thus improvements of the hard magnetic properties of nanocrystalline Zr18-xHfxCo82 ribbons [3]. The investigation of the magnetic microstructure is important for the understanding of these improvements and, more generally, for the development of high-performance magnets. In this paper, emphasis is on local magnetic domain structures in four different samples of rapidly solidified Zr18-xHfxCo82 ribbons with small fractions of Hf (x = 0, 2, 4, and 6). A detailed characterization of magnetic domain-size effects in Zr18-xHfxCo82 ribbons was performed using high resolution magnetic force microscopy (MFM).
EXPERIMENTAL Rapidly solidified nanocrystalline Zr18-xHfxCo82 r
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