Demonstration of additively manufactured NdFeB PPS Halbach magnets to generate variable magnetic fields for neutron reflectometry*

Halbach arrays are the most efficient closed structures for generating directed magnetic fields and gradients, which are widely applied in various electrical machines. However, Halbach arrays require multiple magnet pieces that are exactly alike and are oriented in a specific pattern, which makes them challenging to traditionally manufacture. We utilized the fused deposition modeling-based Big Area Additive Manufacturing technology to print customized, compensated concentric Halbach array discs, using polyphenylene sulfide -bonded NdFeB permanent magnets for polarized neutron reflectometry. The discs could generate a 0 ≤ B ≤ 0.30 T field and demonstrated 90% polarization conservation of a traversed neutron beam. Such a setup will be widely useful for generating additional magnetic contrast and for phase recovery in polarized neutron reflectometry, for magnetic multi-layers, heterostructures, biological membranes, and interfaces.