Domain wall pinning by fine precipitates

Author

Ishikawa, T. ; Hamada, Y. ; Ohmori, K.

Author_Institution

Sumitomo Metals Mining Co. Ltd., Ichikawa, Japan

Volume

25

Issue

5

fYear

1989

fDate

9/1/1989 12:00:00 AM

Firstpage

3434

Lastpage

3436

Abstract

The addition of Nb to the Nd-Fe-B-type magnet causes precipitates to form within the hard magnetic grain. Domain-wall pinning effects of the precipitates were investigated by measuring an initial magnetization curve and by domain-wall observation in a magnetic field using Lorentz microscopy. Precipitates which were 500 A in size and 10¹⁵ nuclei/cm³ in density were produced in an Nb-doped (Nd,Dy)-Fe-B sintered magnet and found to contain Nb. A Lorentz micrograph showed that the domain walls pass through the precipitates. The initial magnetization increased abruptly, which indicates that the magnetization process is still nucleation-type. It was observed that almost all walls disappear under application of an external field of 5 kOe. It is concluded that the pinning effect is not strong enough to produce a significant increase in the coercive force of the permanent magnet and that the suppression of grain growth by niobium addition is the cause of the improvement of the coercivity

Keywords

alloying additions; boron alloys; coercive force; dysprosium alloys; ferromagnetic properties of substances; iron alloys; magnetic domain walls; magnetisation; neodymium alloys; niobium alloys; permanent magnets; precipitation; scanning electron microscope examination of materials; sintering; Lorentz micrograph; Lorentz microscopy; NdDyFeB:Nb sintered magnet; SEM; coercive force; domain wall pinning effect; domain-wall; fine precipitates; grain growth; hard magnetic grain; magnetization curve; nucleation; permanent magnet; Annealing; Coercive force; Demagnetization; Magnetic domain walls; Magnetic domains; Magnetic field measurement; Magnetization processes; Niobium; Petroleum; Scanning electron microscopy;

fLanguage

English

Journal_Title

Magnetics, IEEE Transactions on

Publisher

ieee

ISSN

0018-9464

Type

jour

DOI

10.1109/20.42326

Filename

42326