Relation between the Mechanical Output of a Small Stepping Motor and the Intrinsic Coercivity of an Unsaturated α-Fe/R2Fe14B Nanocomposite Bonded Magnet (R=Pr and Nd)

Abstract

The miniaturization of electric motors such as small stepping motors has progressed rapidly, and has been accompanied by a drastic decrease in the mechanical output of the motors relative to the reduction in size. One of the causes of this decrease is insufficient magnetization in the magnets used in motors because of a decrease in the pole-pitch. Since so-called nanocomposite flakes are easily magnetized in comparison with conventional Nd₂Fe₁₄B melt-spun flakes, we used bonded-magnet rotors prepared from α-Fe/R₂Fe₁₄B nanocomposite melt-spun flakes with high remanence in small stepping motors, and studied the effects of the coercivity and remanence of the flakes on the magnetic stability of the magnets and the characteristics of the motors. As a result, when the nanocomposite flakes had a coercivity of 600-700 kA/m and a remancence higher than 950 mT, the motors exhibited adequate magnetic stability atoperating temperature as well as a higher mechanical output than that obtained using a conventional Nd₂Fe₁₄B bonded magnet.