Magnetic Field Alignment of the Anisotropic Spray Dried Nd-Fe-B Powder

Abstract

A process to obtain the anisotropic spray dried Nd-Fe-B powder has been studied in order to improve the poor alignment of sintered magnets synthesized by the usual isotropic spray dried powder. A magnetic field of 0.12 MA/m was applied transversely to the flow of droplet where it dried up to be granulated powder which has a good flowability. The measurement of the initial magnetization curve and the X-ray diffraction patterns revealed that the easy axis of powders aligns to the direction of the external field more easily compared with the isotropic powder
spray dried in the same condition without a magnetic field. It suggests that our spray dried powder is anisoptropic; Nd-Fe-B fine powder included in each granular is uniaxially aligned. The alignment of the anisotropic spray dried powder in a low field is dominated by the rotation of granulated powder. When the strength of the magnetic field at compacting is 0.23 MA/m, (BH)max of the sintered magnet obtained from the anisotropic spray dried powder exceeds by 19.2 % than the value for the isotropic one.