Magnetic flux loss in rare-earth magnets irradiated with 200 MeV protons

The effects of 200 MeV proton irradiation on the magnetic flux of Nd-Fe-B and Sm-Co magnets have been investigated over the dose range from similar to 10(2) Gray to similar to2 x 10(5) Gray. Nd-Fe-B magnets with coercive force H-cj 1.15 MA/m and 2.5 MA/m were used as samples, where their permeance coefficient P-c was 0.5 similar to 2.0. The magnetic flux of Nd-Fe-B magnets decreased as the proton dose increased, while the flux of Sm-Co magnet did not change. The relation between the flux loss Delta Phi of Nd-Fe-B magnets and the absorbed dose D was expressed as Delta Phi = -eta log D + const., where value eta was 39 +/- 3% with D in Gray. The absorbed dose D-20, which caused the flux loss of 20%, was 5.1 x 10(2) Gray for P-c = 0.5, 2.0 x 10(3) Gray for P-c = 1.0, and 6.8 x 10(3) Gray for P-c = 2.0 in case of Nd-Fe-B magnets with H-cj = 1.15 MA/m. The dose D-20 was 2.3 x 10(4) Gray for P-c = 0.5, and 2.9 x 10(5) Gray for P-c = 2.0 in case of Ne-Fe-B magnets with H-cj = 2.5 MA/m. Increase of both of permeance coefficient and coercive force led to the enhancement of the resistance to the radiation-induced damage. (C) 2001 Published by Elsevier Science B.V.