We previously reported that an advanced preparation method was applied to the synthesis of a radially anisotropic composite bonded magnet with a continuously controlled direction of anisotropy for inner and outer rotor magnets. The preformed magnets were extruded and compressed into ring-shaped magnets by using self-recoverability based on the incomplete three-dimensional (3-D) network molecular structure at an elevated temperature. In this study, an investigation of the thermomechanical behavior of the self-recoverability of the magnets together with their magnetic properties was carried out in order to apply them to small motors as various specific shapes. As a result, the (BH)max of a magnet attained a typical value of 165 kJ/m 3 , and no deterioration of magnetic properties was detected throughout the preparation process even if the magnets were miniaturized at weights ranging from 38 to 400 mg. The reduction in size is attributed to the optimized incomplete 3-D network molecular structure.

Abstract. We have already reported an advanced method for producing a radially-anisotropic rare earth composite bonded magnet with continuously controlled direction of anisotropy. The magnet has been applied to an inner rotor as a practical usage. In this study, the outstanding preparation method was adopted into the preparation of a magnet applied for an outer rotor. An optimized condition of extrusion and compaction at an elevated temperature could be obtained. In addition, a low pressure configuration to the ring-shaped magnet from plural preformed magnets was carried out, which had specific distribution of magnetic anisotropy for internal space for a small motor, by using self recoverability based on the viscous deformation without an alignment field. No deterioration of magnetic properties was detected through the process even if those magnets were miniaturized. Resultantly, the (BH) max of a ring-shaped magnet with the continuously controlled direction of magnetic anisotropy attained the value of 186 kJ/m 3 , and we obtained sine-wave magnetic anisotropy distribution, even if those magnets were miniaturized. IntroductionFurther improvements in performance of small motors are strongly required from the standpoints of environment protection and saving of resources. In order to realize a high efficiency motor, a miniaturized magnet with excellent magnetic properties is indispensable.This contribution reports an optimized preparation process for an arc-shape magnet with continuously controlled direction of anisotropy by taking advantage of the previously reported technique [1] in order to apply it to an outer rotor. The magnetic properties of the arc-shaped magnets did not degrade through the process. It was also clarified that the direction of anisotropy in the ring-shaped magnets can be controlled continuously under an application of an alignment field with one direction together with a mechanical design of preformed magnets before deformation. Finally, we succeeded in obtaining a 12 pole ring shaped magnet with (BH) max and remanence values of 186 kJ/m 3 and 1.03 T, respectively, and static magnetic field for internal space can be detected.

In the preparation of a miniaturized rotor, a composite bonded magnet was fabricated by taking advantage of self-recoverability. A preformed magnet was synthesized by using incomplete three-dimensional network molecular structure which was formed under the optimum conditions at a temperature of 433 K, an alignment field of 1.4 MA/m, and a low compacting pressure of 50 MPa, respectively. The preformed ones were extruded and compressed into a ring-shaped magnet by using the self-recoverability at a pressure of 200 MPa and a temperature of 423 K under non-alignment-field. Through the process, a composite bonded magnet rotor in the shape of a ring could be prepared without a bonding layer. It was clarified that a 4 pole/6 slot DC brush less motor can be obtained by using the ring-shaped rotor comprising a parallel oriented anisotropic magnet with 7 mm in outer diameter, 158 kJ m 3 in (BH) max , and 6.2 Mg m 3 in density, respectively. Resultantly, the developed rotor enabled us to increase the S-T gradient by 1.75 times compared with that for a conventional isotropic Nd-Fe-B bonded magnet rotor with the same dimensions.Index Terms-Anisotropic bonded magnet rotor, anisotropic rare earth bonded magnet, DC brushless motor, self-recoverable binder system.