Hard magnetic materials based on Nd 9 (Fe, B) 87 Zr 2 Nb 2 nanograined intermetallic compounds
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Hard magnetic materials based on Nd9(Fe,B)87Zr2Nb2 nanograined intermetallic compounds Shoichi Kumon1, Kazue Nishimoto1, Tomokazu Fukuzaki2 and Ryuji Tamura1, 2 1 Dept. of Mater. Sci. and Tech., Tokyo University of Science, Noda, Chiba, Japan 2 Polyscale Technology Research Center, Tokyo University of Science, Noda, Chiba, Japan ABSTRACT Magnetization behavior of Nd9(Fe, B)87Zr2Nb2 nanostructure magnets have been investigated. We will show that the nanostructure magnets are composed of magnetic clusters of exchange-coupled single domains and the coercivity is governed by coupling intensity between soft and hard magnetic clusters in the magnets. INTRODUCTION Low rare-earth Nd-Fe-B nanocomposites which consist, on a nano scale, of a Nd2Fe14B hard magnetic phase and soft magnetic phases such as α-Fe and/or Fe-B compounds, are expected to be excellent candidates for future applications as magnetic materials because of a number of advantages over the conventional sintered magnets, such as their low rare earth content, high corrosion resistance, high magnetic polarization due to remanence enhancement as well as to the presence of the soft phase, etc. The high magnetic polarization of nanocomposites is attributed to magnetic coupling between the soft magnetic phase and the hard phase [1]. It has been reported that the high coercivity HcJ is obtained in Nd9Fe73B14M4 (M : substituted elements) nanocomposites [2, 3], and significantly high HcJ value has been reported for Nd9Fe73B14Zr2Nb2 nanocomposite by the addition of elements having high glass formation ability [3]. Recently, we have reported that an excellent maximum energy product (BH)max and an extraordinary high coecivity are obtained by controlling the volume fraction of the soft phase, i.e., α–Fe, in Nd9Fe79B8Zr2Nb2 and Nd9Fe79B8Zr2Nb2 nanocomposites, respectively [4]. The purpose of the present paper is to clarify the relation between the nanostructure and the magnetization mechanism of Nd9Fe79B8Zr2Nb2 and Nd9Fe73B14Zr2Nb2 by investigating their magnetic hysteresis and recoil loops. EXPERIMENTAL Alloy ingots of nominal compositions Nd9Fe79B8Zr2Nb2 and Nd9Fe73B14Zr2Nb2 were prepared by using high purity raw materials of Nd (3N), Fe (4N), B (2N5), Zr(3N) and Nb (3N) in an arc furnace under an Ar atmosphere. Then the alloys were melt-spun onto a Cu wheel rotating with the surface velocity of 18.6 (for 79 at.%Fe) and 12.5 (for 73 at.%Fe) m·s-1 under the Ar atmosphere. The melt-spun ribbons were then sealed inside a quartz tube in an Ar atmosphere and annealed at 813 K (for 79 at.%Fe) and 993 K (for 73 at.%Fe) for 240 s. The obtained phases were probed by X-ray diffraction (XRD) and the microstructures of the samples were investigated using a transmission electron microscope (TEM). The magnetic properties of the
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samples were measured by a vibrating sample magnetometer (VSM) in the applied magnetic field up to 10 T.
RESULTS AND DISCUSSION
Figure 1: XRD patterns of annealed Nd9Fe79B8Zr2Nb2 and Nd9Fe73B14Zr2Nb2 alloys.
Figure 2: Bright Field TEM images of annealed
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