TY - JOUR
T1 - Magnetization measurements for grain boundary phases in Ga-doped Nd-Fe-B sintered magnet
AU - Niitsu, K.
AU - Sato, A.
AU - Sasaki, T. T.
AU - Sawada, R.
AU - Cho, Y.
AU - Takada, Y.
AU - Sato, T.
AU - Kaneko, Y.
AU - Kato, A.
AU - Ohkubo, T.
AU - Shindo, D.
AU - Hono, K.
AU - Murakami, Y.
N1 - Funding Information:
This study was supported by JST, CREST, dedicated to the improvement of coercivity in Dy-free Nd-Fe-B permanent magnets. A part of the analysis using a large number of phase images was supported by another project of JST, CREST (JPMJCR1664), dedicated to the enhancement of sensitivity in electron holography. The authors are grateful to Dr. K. Harada, and Dr. T. Tanigaki for useful discussions about the electron holography observations.
Funding Information:
This study was supported by JST , CREST , dedicated to the improvement of coercivity in Dy-free Nd-Fe-B permanent magnets. A part of the analysis using a large number of phase images was supported by another project of JST, CREST ( JPMJCR1664 ), dedicated to the enhancement of sensitivity in electron holography. The authors are grateful to Dr. K. Harada, and Dr. T. Tanigaki for useful discussions about the electron holography observations.
Publisher Copyright:
© 2018 Elsevier B.V.
PY - 2018/7/5
Y1 - 2018/7/5
N2 - The magnetism of grain boundary (GB) phases in the Nd-rich Ga-doped Nd-Fe-B sintered magnet that shows unusually high improvement in coercivity by post-sinter optimal heat treatment was studied using electron holography. Transmission electron microscopy observations identified three types of GB phases with distinct structures, i.e., Ia3¯-type, amorphous-type, and Nd6(Fe,Ga)14-type. The magnetic flux densities of these three GB phases were systematically analyzed by measuring the phase shifts of incident electrons, and all of these GB phases are concluded to be nonferromagnetic. Unlike the standard commercial sintered magnets, this study has shown that the Nd2Fe14B grains in the optimally heat treated Nd-rich Ga-doped sintered magnet are exchange decoupled by the formation of the three types of nonferromagnetic GB phases. The observations provide useful information for GB engineering of Nd-Fe-B sintered magnets, which is key for further improvements of their coercivities without relying on grain size refinement.
AB - The magnetism of grain boundary (GB) phases in the Nd-rich Ga-doped Nd-Fe-B sintered magnet that shows unusually high improvement in coercivity by post-sinter optimal heat treatment was studied using electron holography. Transmission electron microscopy observations identified three types of GB phases with distinct structures, i.e., Ia3¯-type, amorphous-type, and Nd6(Fe,Ga)14-type. The magnetic flux densities of these three GB phases were systematically analyzed by measuring the phase shifts of incident electrons, and all of these GB phases are concluded to be nonferromagnetic. Unlike the standard commercial sintered magnets, this study has shown that the Nd2Fe14B grains in the optimally heat treated Nd-rich Ga-doped sintered magnet are exchange decoupled by the formation of the three types of nonferromagnetic GB phases. The observations provide useful information for GB engineering of Nd-Fe-B sintered magnets, which is key for further improvements of their coercivities without relying on grain size refinement.
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U2 - 10.1016/j.jallcom.2018.04.055
DO - 10.1016/j.jallcom.2018.04.055
M3 - Article
AN - SCOPUS:85045648881
SN - 0925-8388
VL - 752
SP - 220
EP - 230
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
ER -