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Thermoplastic bonded magnetic composites combine the cost-effectiveness, low mass density, and manufacturing flexibility of conventional thermoplastics with the unique characteristics of magnetic powders/ fillers to form multifunctional magneto polymeric composites that offer superior properties to conventional materials. At elevated temperatures, the magnetic properties change significantly, and the polymer matrix no longer secures the magnetic particles and can rotate freely with respect to an externally applied magnetic field. This often happens at temperatures significantly below the melting point of the polymer. To extend the thermal window of bonded magnets beyond 175 ◦C (the typical temperature of rotors in motors and generators), poly- mers such as polyetheretherketone (PEEK), polyetherimide (PEI), or other high-temperature thermoplastics have been considered suitable binders for magnetic fillers. Another suggested approach is using a surface treatment to increase the adhesion between the polymer matrix and magnetic particles. In this review, the fabrication pro- cesses to make bonded magnets by injection molding and fused filament fabrication were discussed as well as their thermal, mechanical, and magnetic performance obtained via analytical and materials characterization methods. The magnetic properties of bonded permanent magnets manufactured via different techniques were discussed in terms of the most important single magnetic parameter known as “the maximum energy product- (BH)max, which can serve as a performance index for manufacturing bonded magnets. The energy product normalized on cost or mass density are used to provide insight on the performance of bonded magnets for ap- plications driven by cost or inertia. Finally, applications of high-performance thermoplastic-based magnetic composites that can be viable for stringent engineering devices such as sensors, actuators, motors, and generators were highlighted. 

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. 

Texas State University received an NSF S-STEM award to support two cohorts of talented, low-income engineering majors, with the first cohort starting their freshman year in Fall 2024. In addition to the scholarships awarded, this program aims to increase students’ engineering design self-efficacy, engineering identity, and improve persistence to graduation. The program includes unique strategies for achieving these goals, emphasizing mentoring and building a sense of community among participants. The SEED scholars were paired with a faculty mentor in their engineering major prior to their arrival on campus for their freshman year. This early contact was intended to open lines of communication with a faculty member, so the students felt they had a trustworthy source of information from someone who cared about them. As Texas State University has a high number of first-generation college students, there was an expectation that this program would likely attract a fair number of first-generation students. Without another family member’s experience about how to be a college student, having this faculty mentor gave these students a person who could help them answer questions and navigate the process leading to their first semester on campus. For instance, mentors were able to talk with students about dorm selection, mathematics course placement (including strategies for placing into a higher-level mathematics course), and what to expect in their engineering coursework. Student participation in an Engineering Living Learning Community (LLC) is another unique program feature to enhance community among the SEED scholars. A general description of the program and preliminary results from the students’ self-reported sense of belonging in engineering, engineering design self-efficacy, and engineering identity are presented in this paper. 

Magnetic Field Assisted Additive Manufacturing (MFAAM), 3D printing in a magnetic field, has the potential to fabricate high magnetic strength anisotropic bonded magnets. Here, 10, 35, and 54 wt% strontium ferrite bonded magnets using polyamide 12 binder were developed by twin screw compounding process and then printed via MFAAM samples in zero, and in 0.5 Tesla (H parallel to the print direction and print bed). The hysteresis curves were measured using a MicroSense EZ9 Vibrating Sample Magnetometer (VSM) for 3 different mount orientations of the sample on the sample holder to explore the magnetic anisotropy. The samples printed in zero field exhibited a weak anisotropy with an easy axis perpendicular to the print direction. This anisotropy is caused by the effect of shear flow on the orientation of the magnetic platelets in the 3D printer head. For the MFAAM samples, the S values are largest along the print bed normal. This anisotropy is caused by the field. The alignment of the magnetic particles happens when the molten suspension is in the extruder. When the material is printed, it is folded over on the print bed and its easy axis rotates 90° parallel to the print bed normally. Little realignment of the particles happens after it is printed, suggesting a sharp drop in temperature once the composite touches the print bed, indicating that field-induced effects in the nozzle dominate the anisotropy of MFAAM deposited samples. 

The magnetic anisotropy of strontium ferrite (SF)/PA12 filament, a popular hard magnetic ferrimagnetic composites that is used for 3D-printing of permanent magnets, is studied by vibrating sample magnetometry. The studied filaments have a composition of SF/PA-12 thermoplastic composite with a 40% wt.  ratio of SF. SF particles are non-spherical platelets with an average diameter of 1.3 um and a diameter to thickness ratio of 3. Filaments are produced by a twin-screw extruder and have a diameter of 1.5 mm. SEM images show that the SF particles are homogeneously distributed through the filament. VSM measurements on different parts of the filaments show that the outer part of the cylindrical filament has a higher anisotropy, and the core is mostly isotropic. This conclusion is consistent with computational work by others which suggest that particle alignment predominantly takes place near the walls of the extruder die where shear flow is maximum. Additional hysteresis curve measurement of the outer cylindrical part of the filament parallel to the r and ϕ directions indicates that the squareness of the hysteresis curve (S) is larger in the r-direction. This indicates that the outer surface of the filament has a strong easy axis in the r-direction. We conclude that the SF platelets line up parallel to the walls of the extrusion die. 

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.