Aftereffect measurements have been performed on synthetic ferrimagnets showing strong perpendicular magnetic anisotropy, namely (Co/Pt)/Ir/(Co/Pt), by measuring the magnetization of the sample as a function of time for several different applied magnetic fields. Unexpected magnetic relaxation has been observed. Indeed, for some particular applied magnetic fields, the magnetization as a function of time first plummets and then increases. This nonmonotonic aftereffect can be understood by considering the possible magnetic states and the transitions between those states. This understanding has been confirmed and detailed using magneto-optical Kerr effect (MOKE) microscopy. Indeed, the measurements show nucleation and propagation of a transient metastable magnetic configuration. Furthermore, we were able to obtain a good qualitative agreement between a simple one-dimensional model and the experimental observation. We could strongly support the hypothesis that this peculiar nonmonotonic behavior could be a very general feature that should be observed in any antiferromagnetically coupled system (synthetic ferrimagnets, synthetic antiferromagnets) with perpendicular magnetic anisotropy.

The removal of heavy metals from wastewater is an environmental challenge which demands the use of environmentally friendly materials that promote a circular economy. This study aimed to apply a novel composite of an activated nanoclay/hydrocolloid in the removal of heavy metals from wastewater. A composite blended under pressure was prepared with spray-dried hydrocolloid derived from Nostoc sphaericum algae and activated nanoclay in an acid medium and 1M NaCl. The composite and components were analyzed through infrared (IR), X-ray (XR), ζ potential, cation exchange capacity (CEC), particle size, and SEM images. The composite was subjected to the adsorption of heavy metals (Pb, As, Zn, and Cd) at pH 4.5 and the removal percentage, kinetics, and adsorption isotherms were evaluated. It was observed that the activated nanoclay and the composite that presented a particle size of around 400 nm significantly increased (p-value < 0.05) the CEC, ζ potential, the functional groups, and chelating components, removing heavy metals above 99% for Pb, As 33%, Cd 15%, and Zn 10%. Adsorption kinetics was adjusted to the pseudo second-order model (R² > 0.98), and the Langmuir and Freundlich models better represented the sorption isotherm at 20 °C. The formulated composite presents a good ability to remove heavy metals in wastewater.

Mechanical behavior of hydroxyapatite-based composites (HAp) was studied as a function of the reinforcement concentration of the quasicrystalline (QC) Al₆₄Cu₂₃Fe₁₃ alloy. The synthesis of the HAp matrix was carried out by sol-gel method, while the synthesis of the QC was performed by an arc furnace with a subsequent thermal treatment. The composites were made by powder metallurgy and cold compacted to form test pieces that were sintered with a constant flow of argon. The materials were characterized using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and Fourier transform Raman spectroscopy. The study of mechanical strength was carried through compression tests. The biocompatibility of the composites was tested using an in-vitro cytotoxicity assay. The mechanical resistance of HAp/QC composites increased with the concentration of quasicrystalline reinforcement. Young’s modulus and compressive strength increased in 43% and 21%, respectively, with a 10 wt% QC reinforcement, which demonstrates an hybrid behaviour of the composite due to the inclusion of reinforcing particles in the pores of the matrix. This composite did not show cytotoxicity at any of the QC concentrations. A fabrication route is proposed as a fast, easy and high efficiency alternative for applications in the biomedical industry because of its high scalability potential.