Positive Temperature Coefficient of Magnetization Characteristic for Composite Plastic-Bonded Magnet Composed of Nd₂Fe₁₄B and SrO·6Fe₂O₃

Abstract

Plastic-bonded magnets were prepared by magnetic field injection molding, using a mixture of Nd₂Fe₁₄B and SrO·6Fe₂O₃ pellets. The magnetic characteristics and temperature coefficients of these magnets were investigated. The hysteresis loop for the temperature change of the plastic-bonded magnet was measured. An important phenomenon was revealed pertaining to the physical properties of the magnetic material: under ordinary temperature conditions, the magnetic temperature coefficient of magnetic flux density and coercive force for the Nd₂Fe₁₄B and SrO·6Fe₂O₃ plastic-bonded magnet for the case of adequate SrO·6Fe₂O₃ content attained a positive value at a SrO·6Fe₂O₃ content ranging from about 20 to 60 mass% at 297–323 K, and from around 18 to 43 mass% at 323–373 K. Moreover, it was proven that the temperature coefficients of the magnetic flux density at operating points of permeance coefficients P_c(B⁄H)=1 and 2 could be controlled from 0 to 0.22%/K at 297–323 K and from 0 to 0.1%/K at 323–373 K, respectively.