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 ∼102 Gray to ∼2x105 Gray. Nd-Fe-B magnets with coercive force Hcj 1.15 MA/m and 2.5 MA/m were used as samples, where their permeance coefficient Pc was 0.5∼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 ΔPHI of Nd-Fe-B magnets and the absorbed dose D was expressed as ΔPHI=-ηlog D+const., where value η was 39±3% with D in Gray. The absorbed dose D20, which caused the flux loss of 20%, was 5.1x102 Gray for Pc=0.5,2.0x103 Gray for Pc=1.0, and 6.8x103 Gray for Pc=2.0 in case of Nd-Fe-B magnets with Hcj=1.15 MA/m. The dose D20 was 2.3x104 Gray for Pc=0.5, and 2.9x105 Gray for Pc=2.0 in case of Ne-Fe-B magnets with Hcj=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