Two-powder Nd{sub 2}Fe{sub 14}B magnets with DyGa-addition

Journal Article · Thu Jan 01 04:00:00 EST 1998 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.366734· OSTI ID:565618

de Groot, C H; Buschow, K H; de Boer, F R ^[1]; de Kort, K ^[2]

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1. v/d Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam (the Netherlands)
2. Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven (the Netherlands)

Magnetic and structural properties of sintered NdFeB magnets with addition of various amounts of DyGa as a separate powder are studied and compared with single-powder magnets of the same nominal composition. When the magnets are annealed above 640{degree}C, the coercivity decreases strongly as compared to magnets annealed below 640{degree}C. Decomposition of the {delta} phase (Nd{sub 6}Fe{sub 14{minus}x}Ga{sub x}) accompanies this drop. Measurements of coercivity as a function of temperature show that the decomposition of the {delta} phase does not increase the effective demagnetization factor, but enlarges either the magnetic inhomogeneous region at the grain surface or the exchange coupling between the grains. Line faults, which are present within the Nd{sub 2}Fe{sub 14}B grains when the magnet is annealed below 640{degree}C, do not act as pinning centers. Phase analysis and diffusion profiles of the Dy and Ga concentration within the grains are made using electron probe micro-analysis. This shows that Ga forms Nd{sub 3}Ga{sub 2} and Nd{sub 6}Fe{sub 12.7}Ga{sub 1.3} as intergranular phases. Its concentration within the {Phi} phase is significantly lower than in the {Phi} phase of single-powder magnets. At 1090{degree}C, a diffusion coefficient for Ga of D=2.5{plus_minus}0.1{times}10{sup {minus}15} m{sup 2}/s is found. Dy is shown only to be present in that part of the Nd{sub 2}Fe{sub 14}B grain which has precipitated from the liquid during sintering. At the boundary of the Dy-free center and the outer part of the grain, an increased Dy concentration is found. {copyright} {ital 1998 American Institute of Physics.}

• OSTI ID: 565618
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 1 Vol. 83; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANNEALING
BORON ALLOYS
COERCIVE FORCE
DEMAGNETIZATION
DIFFUSION
DYSPROSIUM ADDITIONS
DYSPROSIUM ALLOYS
GALLIUM ADDITIONS
GALLIUM ALLOYS
GRAIN BOUNDARIES
IRON ALLOYS
MAGNETIZATION
NEODYMIUM ALLOYS
PERMANENT MAGNETS
PHASE STUDIES
PRECIPITATION