Magnetic Properties of Nd-Fe-B-M (M=Si, C) Bulk Nanocomposite Magnets Prepared by the Spark Plasma Sintering Method
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1032-I11-02
Magnetic Properties of Nd-Fe-B-M (M=Si, C) Bulk Nanocomposite Magnets Prepared by the Spark Plasma Sintering Method Tomokazu Fukuzaki1, Keisuke Tanaka2, Kazue Nishimoto2, Yuji Muro3, Keishi Nishio2, and Ryuji Tamura2 1 Polyscale Technology Research Center, Tokyo University of Sicence, 2641, Ymazaki, Nodashi, Chiba-ken, 278-8510, Japan 2 Department of Materials Science and Technology, Tokyo University of Science, 2641, Yamazaki, Noda-shi, Chiba-ken, 278-8510, Japan 3 Department of Physics, Tokyo University of Science, 2641, Yamazaki, Noda-shi, Chiba-ken, 278-8510, Japan ABSTRACT We have prepared Nd2Fe14B/Fe3B bulk nanocomposite magnets at the compositions Nd4Fe77.5B18.5-xMx (M=Si, C) by substituting other elements M for B. For the sample substituted with 1 at.%Si, the coercivity exhibits the highest value of 227 kA/m when sintered at 600 oC. In addition, the grain sizes of the Nd2Fe14B and the Fe3B phases are found to depend on the rampup time during sintering and the reduction of the grain size leads to an increase of the coercivity. On the other hand, the samples substituted with C exhibit soft magnetic behaviors, which is attributed to the suppression of the Nd2Fe14B hard phase. INTRODUCTION Nanocomposite Nd-Fe-B bulk magnets are expected as next generation magnets since they have a high potential to exhibit excellent magnetic properties (high coercivity, high remanence and high maximum energy products). Nanocomposite bulk magnets are currently produced using a spark plasma sintering (SPS) method through crystallization process from meltspun amorphous ribbons [1, 2]. The maximum energy product BHmax of a nanocomposite magnet, which is the most important factor for hard magnets, can be improved by increasing either the coercivity Hcj or the residual magnetic polarization Jr. Here, the Hcj value is determined by the geometry of the hard magnetic phase such as the grain size, the grain shape, etc. and the Jr value is determined by the saturation polarization Js and the anisotropy of the soft magnetic phase. An excellent glass forming ability has been reported for the Nd-poor composition of Nd4Fe77.5B18.5 [3] and a bulk nanocomposite magnet can be obtained by heat treatment of a metallic glass prepared at the composition. The resulting Nd4Fe77.5B18.5 nanocomposite magnet is composed of the Nd2Fe14B hard phase and the Fe3B soft phase. However, since Js of the Fe3B and the Nd2Fe14B phases are nearly the same, i.e., 1.6T, the precipitation of the Fe3B phase does not improve Js of the nanocomposite. Therefore, it is of a great interest to investigate the effect of the substitution of other elements on the soft phase, since any phase change of the soft phase would affect the Js value. In this study, we have investigated the magnetic property of Nd2Fe14B/Fe3B bulk nanocomposite magnets by substituting other elements for B in order to examine its effect on the soft phase. We have prepared samples at the compositions Nd4Fe77.5B18.5-xMx, and, Si and C, which have close atomic radii to that of B, have been selected
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