New MnAlC permanent magnets exhibiting macroscopically-plane magnetic-anisotropy

To fulfill the requirements for radial or circumferential magnetizing applications, MnAlC permanent magnets with a new type of anisotropy have been developed. They were produced by a combined processing of plastic working, i.e., upsetting previously extruded billets of MnAlC permanent magnet alloys in the extrusion axis at 660°C. The direction of easy magnetization was converted into directions perpendicular to the extrusion axis by a small plastic strain induced by the upsetting. Magnetic properties in both radial and tangential directions were equivalent from a macroscopic standpoint, and were much superior to those in the axial direction. Magnetic torque measurements revealed that the direction of easy magnetization of this type of MnAlC permanent magnet lay uniformly in every direction parallel to the plane including both radial and tangential directions. The optimum magnetic properties in "the plane of easy magnetization" were as follows: Br = 4.6 kG, Hc = 2.9 kOe, iHc = 4.1 kOe and BHmax= 4.1 MG.Oe. They were obtained by a nickel doped MnAlC alloy with additional tempering.