Reconfigurable 3D-printable magnets with improved maximum energy product

Conventional magnets use neodymium with added heavy rare earths in order to induce high output and size reduction. Still, deposits of heavy rare-earths such as Dysprosium (Dy) and Terbium (Tb) are disproportionately distributed, so it is important to reduce the amount used due to supply issues and material costs. Additionally, the use of rare-earths in applications that only need modest magnetic properties is misfit and complicates its low-cost production in on-demand shapes. In this paper and as a new concept, reconfigurable rare-earth-free Wax/CoFe2O4 composite magnets were fabricated through 3D-printing. The evolution of the magnetic properties was studied as a function of the magnetic field and CoFe2O4 ferrite content, allowing to tune permanent magnetic magnet response. It was shown that saturation and remnant magnetization increase monotonously with ferrite content, reaching maximum values of 38.6 emu.g-1 and 22.1 emu.g-1, respectively, for the sample with 90% in weight of CoFe2O4 (wt.%). On the other hand, the coercive field (≈2500 Oe) remained constant for all samples. Additionally, the addition of ferrite nanoparticles into Wax increased the Young’s Modulus (0.55 GPa to 4.71 GPa) and improved the thermal stability of the matrix as shown by the increase of the maximum degradation rate temperature and the temperature at which 25 wt.% of the sample is degraded (from 412oC to 429oC and from 393oC to 424oC, respectively). In addition, it was evaluated the (Coercive Field)×(Remanence Field) maximum energy product (HC×BC)MAX, the figure of merit of permanent magnets, being ob-tained the highest value reported in the literature for CoFe2O4-based magnets (i.e., 4.44 MG.Oe for the sample with 90 wt.% of ferrite content). Thus, the present study allowed to establish a new way to prepare reconfigurable printable magnets based on Wax/CoFe2O4 nanoparticles for advanced technologies.