Self-organized giant magnetic structures via additive manufacturing in NdFeB permanent magnets

Abstract

Selective Laser Melting (SLM) was used to produce 3D-printed net shape NdFeB (Neodymium Iron Boron) permanent magnets that exhibit relatively large internal permanent magnetization structures, without exposure to any external magnetizing field. The macroscopic magnetization, M→(r→), does not create a significant magnetic stray field outside the as-produced sample, and is pole avoiding and solenoidal. The permanent magnetization can be detected via the stray field that appears after cutting the sample into pieces. From the field measurements it can be concluded that the magnetization is mainly in the 3D-printing planes which are parallel to M→(r→). Maximum magnetic flux densities of almost 80 mT are recorded 1 mm above the cut surfaces in the air. Dependencies of the effect on SLM process parameters, as well as on the sample size and shape are discussed. Although a deep understanding is still missing, a possible mechanism that may partly explain the formation of these self-organized macroscopic magnetization structures is proposed. The discovered effect may offer new routes for producing magnetized rare earth-transition metal (RE-TM) permanent magnets without using a magnetizer, and it shows that the SLM 3D-printing process can lead to new material behavior.