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Polymer matrix composite materials with magnetic properties obtained by the addition of micron-size particles of neodymium iron boron (NdFeB) and strontium ferrite for fused filament fabrication (FFF) are becoming attractive because of their potential applications in the health and automotive industries. Additionally, the design flexibility and low cost of additive manufacturing processes encourage the scientific community to create the materials and understand the properties of the parts obtained with such methods. For example, the micron-size particles of NdFeB and two different types of strontium ferrites, OP-56 and OP-71, were dispersed in the Polyamide 12 matrix using twin screw extrusion. The monofilaments produced on twin screw extrusion were used to print test samples using an open-source FFF 3D printer. Thermal analysis shows a heat flow improvement in the composites compared to neat polyamide 12. Flexural and tensile strengths of the NdFeB/PA12 and OP-71/PA12 composites were reduced, whereas OP-56/PA12 composites showed an improvement of 6% compared to neat PA12. On the other hand, the tensile moduli of OP-71/PA12, OP-56/PA12, and NdFeB/PA12 composites increased by 5.5%, 48.9%, and 25.13%, respectively. 

To better understand Magnetic Field Assisted Additive Manufacturing (MFAAM) the effect of a magnetic field on the orientation and distribution of magnetic particles in a molten magnetic composite was studied. Vibrating Sample Magnetometer (VSM) measurements were made on Sr-ferrite/PA12 fused deposition modeling filaments of different packing fraction (5 and 40 wt. %). The rotation of the sample’s magnetic moment upon application of a field perpendicular to the easy axis was monitored with a biaxial VSM above the PA12’s softening temperature. The observed magnetic moment transients depend on the temperature, the applied alignment field, the packing fraction, and the initial field-anneal procedure. Longer field-anneals result in larger time constants and seem to induce a hurdle that prevents complete alignment at low temperatures and/or for small fields. Results indicate the molten composite is a non-Newtonian fluid that can support a yielding stress. Scanning Electron microscopy (SEM) images taken on field-annealed samples at 230 °C show strong chaining with little PA-12 left between individual Sr-ferrite particles suggesting that direct particle to particle interaction is the reason for the observed non-zero yielding stress. The melt viscosity of the composite increases with the number of thermal cycles above the melting temperature (T m ). Room temperature (RT) torque magnetometry measurements show that magnetic anisotropy depends on the field annealing process through induced shape anisotropy contributions originating from magnetic particle agglomerates.