Physics / mechanism
NdFeB (neodymium-iron-boron) sintered magnets are the highest-energy-density permanent magnets available: BHmax up to ~420 kJ/m³, coercivity >1 MA/m. Remanence (~1.4 T) drives torque density in motors and actuators. Ferrite (SrFe₁₂O₁₉) sits at ~40 kJ/m³—cheap, corrosion-resistant, but weak. Soft magnetic composites (SMC) are iron-powder compacts: near-isotropic flux paths, low eddy-current losses at high frequency (>1 kHz), enabling 3D flux routing impossible in laminated steel. Key parameters: BHmax, Hcj (intrinsic coercivity), Tc (Curie temp), loss coefficient. NdFeB critical constraint: Dy/Tb heavy-rare-earth content for high-temperature coercivity stability.
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