T. Nishiuchi3, H. Iwai4, Y. Gohda5, K. Hono2, and S. Hirosawa2
1) JASRI / SPring-8, Sayo, Hyogo 679-5198, Japan.
2) ESICMM / NIMS, Tsukuba, Ibaraki 305-0047, Japan.
3) Hitachi Metals, Ltd., Shimamoto, Osaka 618-0013, Japan.
4) NIMS, Tsukuba Ibaraki 305-0047, Japan.
5) The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan.
Abstract:
Importance of microstructures in Nd-Fe-B permanent magnet on its coercivity has become a common understanding in order to obtain the higher performance permanent magnet without using dysprosium. Especially, morphological and magnetic properties of grain-boundary (GB) phase are expected to affect coercivity in association with a pinning effect against domain wall displacement. In a micro-magnetic point of view, a thin-film-like GB phase existing between neighboring Nd2Fe14B grains is preferred to be paramagnetic so as to prevent reversed magnetic domains from expanding into neighboring grains. Although the GB phase had been believed to be paramagnetic for a long time, the recent studies showed convincing results indicating that the GB phase could be ferromagnetic [1-3]. In order to uncover the further details of magnetic properties of the GB phase, we have conducted soft X-ray magnetic circular dichroism (XMCD) experiment in a Nd14.0Fe79.7B6.2Cu0.1 sintered magnet. The result of the experiment indicates that the magnetic moment of Fe in the GB phase has 1.4 μB meaning that the GB phase is ferromagnetic. Moreover, a temperature dependence of the magnetic moments shows that the Curie temperature of the GB phase is lower than that of the main Nd2Fe14B phase by about 50 K [4]. On the other hand, intergranular sub-phases at the triple-junction between main phase grains are thought to be paramagnetic, but are necessary to be investigated because the sub-phases could be a material source to form the film-like GB phase. Therefore, the sub-phases have also been investigated using a synchrotron-radiation-based in-situ X-ray diffraction experiment at elevated temperatures up to 1300 K.
Acknowledgements
The authors are grateful to Drs. J. Kim, K. Sugimoto, M. Suzuki, A. Fujiwara, and M. Takata of JASRI, and Drs. H. Sepehri-Amin and T. Abe of NIMS for fruitful discussions. A part of this work is supported by the Elements Strategy Initiative Center for Magnetic Materials under the outsourcing project of MEXT.
References
[1] H. Sepehri-Amin, T. Ohkubo, T. Shima, K. Hono, Acta Mater. 60, 819 (2012).
[2] Y. Murakami, T. Tanigaki, T. T. Sasaki, Y. Takeno, H. S. Park, T. Matsuda, T. Ohkubo, K. Hono, and D. Shindo, Acta Mater. 71, 370 (2014).
[3] T. Kohashi, K. Motai, T. Nishiuchi, and S. Hirosawa, Appl. Phys. Lett. 104, 232408 (2014).
[4] T. Nakamura, A. Yasui, Y. Kotani, T. Fukagawa, T. Nishiuchi, H. Iwai, T. Akiya, T. Ohkubo, Y. Gohda, K. Hono, and S. Hirosawa, Appl. Phys. Lett. 105, 202404 (2014).
Acknowledgements
The authors are grateful to Drs. J. Kim, K. Sugimoto, M. Suzuki, A. Fujiwara, and M. Takata of JASRI, and Drs. H. Sepehri-Amin and T. Abe of NIMS for fruitful discussions. A part of this work is supported by the Elements Strategy Initiative Center for Magnetic Materials under the outsourcing project of MEXT.
References
[1] H. Sepehri-Amin, T. Ohkubo, T. Shima, K. Hono, Acta Mater. 60, 819 (2012).
[2] Y. Murakami, T. Tanigaki, T. T. Sasaki, Y. Takeno, H. S. Park, T. Matsuda, T. Ohkubo, K. Hono, and D. Shindo, Acta Mater. 71, 370 (2014).
[3] T. Kohashi, K. Motai, T. Nishiuchi, and S. Hirosawa, Appl. Phys. Lett. 104, 232408 (2014).
[4] T. Nakamura, A. Yasui, Y. Kotani, T. Fukagawa, T. Nishiuchi, H. Iwai, T. Akiya, T. Ohkubo, Y. Gohda, K. Hono, and S. Hirosawa, Appl. Phys. Lett. 105, 202404 (2014).