Title :
Domain wall pinning by fine precipitates
Author :
Ishikawa, T. ; Hamada, Y. ; Ohmori, K.
Author_Institution :
Sumitomo Metals Mining Co. Ltd., Ichikawa, Japan
fDate :
9/1/1989 12:00:00 AM
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;
Journal_Title :
Magnetics, IEEE Transactions on
