Rare earth magnets resisting eddy currents

Magnets with high electrical resistance were prepared by electrically isolating Sm₂Co₁₇ and Nd₂Fe₁₄B powder particles. This is achieved by a polymer mixture consisting of epoxy polyester-insulant (EPI), polyvinylbutyral (PVB), epoxy resin (ER) and silane coupling (SC). The properties of interest for anisotropic Sm₂Co₁₇ and isotropic Nd₂Fe₁₄B magnets respectively are ρ=1×10⁵ Ω-cm²/m, Br=6.8 kG, iHc=10.0 kOe, (BH)max=9.2 MGOe in 5%EPI, 4%PVB, 2%ER, 1%SC and ρ=9.4×10⁴ Ω-cm²/m, Br=4.5 kG, iHc=9.5 kOe, (BH)max=13 MGOe in 4%EPI, 3%PVB, 2%ER, 1%SC. The insulated magnets exhibit far better magnetic stability than those of sintered and bonded magnets after magnetizing in radio frequency field. The insulated Sm₂Co₁₇ magnet has the best performance in resisting eddy current. At 500 kHz frequency, 830 Oe magnetizing-field and in one minute, the irreversible loss of recoil remanence is 1.47% and 22.2% respectively for insulated Sm₂Co₁₇ and Nd₂Fe₁₄B magnets