Advances in Superferromagnetic Nanocomposites

Dear Colleagues,

For decades, the increasing consumption of the electrical energy, caused by the necessity to transmit it over large distances, has motivated investigations into soft ferromagnetic materials for power converters. The achieved level of performance in terms of reducing losses is spectacular, and progress is still continuing with regards to large scale applications. Smart houses, smart cars, smart planes, etc., are being designed to reduce overall energy consumption at the expense of the level of electrical energy required to power up the sensors, switches, and motors. With the increasing complexity of smart systems, this energetic cost is becoming noneglible. Challenges in the field of soft ferromagnetic materials derive from the miniaturization of electrical systems, including power transmission lines, particularly on-chip power converters, and from the miniaturization of electric motors. The resulting reduction in the magnetic flux must be compensated for by shifting the operating frequency regime up to sub-GHz or GHz ranges. Such high frequencies are the source of power loss problems due to eddy currents. Another huge difficulty is the frequency dependence of the magnetic response amplitude, which is a rapidly decreasing function in the vicinity of the ferromagnetic resonance (FMR) point, as expressed by the acknowledged Snoek constraint. Nevertheless, the need for a breakthrough in the efficient conversion of energy at high frequencies is increasingly urgent.

A solution to the challenges of reducing high-frequency resistivity and breaking the Snoek constraint, or largely increasing the FMR frequency, can be discovered in the research on the superferromagnetic phases of composite magnetic materials. There are plenty of unknowns in the scientific and technological characteristics of composite magnetic materials; in particular, there are questions related to the limits of the morphological uniformity of nanostructural magnetic composites, intermediary magnetic interactions within the nominally nonmagnetic matrix, and influence of the particle–matrix interface on the ordering of magnetic particles. At the macroscopic level, relatively little is known about the statics and dynamics of superferromagnetic domain structures and the nonlinear dynamics within superferromagnetic domains. An ongoing problem is the optimization of geometry and the induced global anisotropy of superferromagnetic composites in terms of the strength of their high-frequency magnetic responses.     

The widespread interest in the superferromagnetic nanocomposites began with the observation that their magnetoresistance can be dominated by interparticle electron tunneling. However, the opportunities for magnetotransport through nanocomposites are still being explored. For instance, the metallic ions in the matrix, which mediate interparticle ferromagnetic interactions, can be movable under external forcing near the percolation threshold. This allows for an induced metal–insulator transition, thus controlling the magnetoresistivity. While they have been extensively studied for three decades, perhaps superferromagnetic nanocomposites are only just emerging as a significant research area in the field of magnetic (high-density) information storage and processing.    

This Special Issue of Magnetochemistry aims to create a forum of discussion for sharing the latest advances and addressing current challenges in superferromagnetic nanocomposites.

Dr. Andrzej Janutka
Dr. Krzysztof Chwastek
Guest Editors

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