Magnetism: Energy, Recycling, Novel Materials

Magnetism is a field of physics that should be developed within this century in order to enhance its applicability. This Special Issue of Magnetochemistry, entitled ‘Magnetism: Energy, Recycling, Novel Materials’, gathers recent results regarding the synthesis, fabrication, and characterization of novel and/or recycled magnetic materials. This includes those with potential applications related to the enhancement of energy efficiency and the optimization of the magnetic response. This Special Issue belongs to the section ‘Applications of Magnetism and Magnetic Materials’, and thus includes manuscripts related to advances in magnetism. The optimization of the magnetic energy density of permanent magnets or the reduction in power losses in high-frequency soft magnetic materials are linked to energy. Likewise, novel compounds are continuously designed and produced for specific applications. Regarding raw materials, existing research focuses on environmental sustainability through recycling, especially the recycling of magnetic elements such as rare earth elements. Thus, we welcome manuscripts that address the design, modeling, simulation, synthesis, and/or characterization of magnetic materials, as well as review articles. The magnetic properties addressed include functional magnetic magneto-transport properties (such as enhanced magnetic softness, giant magnetic field sensitivity, high magnetoresistance, and large magnetocaloric effects).

Finally, this Special Issue comprises seven papers by eminent researchers who are active in the field. Consequently, some relevant topics are not discussed. Nevertheless, no review papers were submitted. However, I would like to sincerely thank all the authors who contributed to this Special Issue for their dedicated efforts and the outstanding quality of their submissions.

Two papers addressed the application of magnetic devices. The first focused on the development of a novel two-stage 3D-printed Halbach array-based device for magneto-mechanical applications in biomedicine [1]. The application of magnetic fields in medicine (diagnostics, therapy) is well known, and includes technology such as magnetic resonance imaging and magnetic particle hyperthermia. Controlled magneto-mechanics permit the transformation of magnetic energy into mechanical energy (forces, torque), and the fabricated tool is a novel set-up. The experimental analysis is complemented with simulation software. However, future studies, both in vitro and in vivo, are needed to check and optimize its applicability. The second paper improves the energy recovery of magnetic energy-harvesting shock absorbers [2]. It is regarded as a feature paper due to our interest in the energy-harvesting suspension systems present in the automobile and energy-recovery sectors. The amorphous Fe-Ni-based materials used are soft magnetic materials. The authors find that incorporating a core material into the secondary coil significantly increases (six to nine times) the magnetic field for frequencies of 10 Hz and 1 kHz. It should also be remarked that electromagnetic dampers are expected to be employed for the enhancement of high-energy recovery efficiency due to their compatibility with existing suspension systems and compact design. The development of magnetic systems and devices for measuring, improving, and/or controlling the magnetic response will benefit the application of external magnetic fields in areas such as energy, biomedicine, sustainability, microelectronics, security, or transport.

Several papers highlight and are focused on specific novel magnetic materials. Dmitriev et al. [3] study the structure, thermomechanical strength, and physicochemical properties of the mixed basicity iron ore sinter. This material is a raw material that is able to produce iron ore sinter. It is known that sintering is the most economic and widely used agglomeration process for preparing iron ore fines (for blast furnace use). This work proves that the metallurgical properties of sinter are due to the presence of complex silicates, enabling the attainment of high thermomechanical strength (up to 67%). Regarding the basicity, it was found that the basicity increases the shift in the temperature sintering interval.

There are three papers related to novel magnetic materials for energy applications. One paper focuses on thermoelectricity [4] and is related to the magnetic properties (magnetic susceptibility, magnetic moment) of transition and rare-earth metal dichalcogenides. In Cu-Cr-La-S compounds, the percentage of Cr and La can be modified; these compounds are hybrid materials that combine magnetic, thermoelectric, electrophysical, and optical properties. In this paper, it is found that the combination of cationic substitution and intercalation (alternating chalcogenide-metal-chalcogenide layers) enhances the functional multi-response. Concerning thermoelectric behavior, it is also found that the alloy with the highest Seebeck coefficient is CuCr_0.99La_0.01S₂. The magnetic analysis includes the determination of the Weiss constant.

Two other papers focus on magnetocaloric materials [5,6] whose main characteristic is their magnetocaloric effect. The application of an external magnetic field shifts the temperature and induces magnetic and/or structural transformations. Thus, these materials can be employed in magnetic refrigeration as an eco-friendly alternative to conventional compression-gas-based refrigeration systems. Alloys with a higher magnetocaloric response usually include rare-earth elements. Due to their accessibility and cost, in recent decades, scientific and technological research has increasingly focused on rare-earth-free elements. Two works are devoted to Ga-free Heusler alloys, where the temperature working interval depends on the composition. Here, the compositions are off stoichiometric if the desired interval is close to room temperature. Ni-Mn-In melt-spun ribbons have been produced by melt-spinning [5]. The magnetocaloric analysis includes the modeling of critical behavior, finding that the best model is the mean field model due to the long-range order of the ferromagnetic interactions. Likewise, the experimental results of the thermodynamic parameters are compared with those calculated by applying the Landau theory, proving that the agreement is good. The magnetocaloric behavior is like that of Heusler alloys with a similar composition. Ni-Mn-Sn bulk alloys have been produced by the Bridgman-type directional solidification method [6]. Ni-Mn-In alloys have a similar magnetocaloric behavior to that of Ni-Mn-Sn alloys, but a shift in the characteristic temperatures is found in alloys with an equivalent composition. In this study, the magnetocaloric effect analysis is complemented by evaluations of the electrical resistivity and mechanical properties (compressive stress–strain curves), as these properties are applicable to magnetic sensors and/or actuators.

Regarding the application of a specific treatment to magnetic materials, Kumar et al. [7] studied the magnetorheological finishing of chemically treated electroless nickel plating. These electrodes can be applied in several fields, including electronics, the automotive industry, and optics. For example, in optics, magnetorheological finishing is a lens-surface-finishing process that improves the development of precision optical components such as space mirrors. However, the surface roughness must be reduced to the nanometric scale. In this paper, it is found that optimized chemical treatment significantly reduces the roughness (minimum value 10 nm). It also recommends optimizing the micro- and nanohardness. Generally, in materials science and technology (including magnetic materials), nanoscale research remains an important field of interest.

Finally, I would like to express my gratitude to the editorial team at Magnetochemistry for their unwavering support and commitment, as their assistance has played a crucial role in preparing and finishing this Special Issue.