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Cobalt ferrites exhibit widely varied magnetic behaviour due to the presence of a miscibility gap leading to the formation of periodic self-assembled nanostructures via spinodal decomposition. Periodicity and amplitude of the compositional fluctuations can be controlled by thermodynamic and kinetic processing parameters which allows for careful tuning of the magnetic properties. Although reports have shown evidence of spinodal decomposition, there is a lack of detailed characterization of the magnetic interactions and reversal mechanisms in these materials. In this work we use high-resolution first order reversal curves (FORC) measurements to understand the underlying magnetic processes occurring in a cobalt ferrite with a nominal composition of Co1.8Fe1.2O4 before (calcined) and after spinodal decomposition (annealed). Additionally, FORC measurements with preconditioning fields were conducted to separate the interaction signatures at low coercive fields by biasing the sample in positive and negative mean fields. Microstructural characterization using TEM combined with EDS showed uniform chemistry in the calcined sample and the presence of Fe rich and Co rich regions in the annealed sample, due to spinodal decomposition. Signs of positive exchange interactions were observed in both calcined and annealed samples. This work presents the first detailed magnetic characterization of magnetic interactions in a nanostructured cobalt ferrite, and provides an example of magnetic characterization of nanostructured ferrites using FORC.

Magnetic ceramics are important for numerous technologically relevant applications with a detailed understanding of structure, property, and processing inter-relationships playing a critical role in tailoring magnetic properties. Spinel ferrites are a particularly interesting class of magnetic ceramics of chemical formula AB2O4, with applications including biomedical hyperthermia and high frequency electrical power conversion. In this contribution, we seek to investigate a unique class of Co-ferrites in which spinodal decomposition can produce a ferrite nanocomposite with chemistry and stress state fluctuating within the interior of crystalline grains on the nm-scale, resulting in corresponding fluctuations of intrinsic magnetic properties as well as exchange and magnetostatic interactions. Structural and magnetic characterization of spinel ferrite samples are carried out (1) in the as-milled state prior to thermal processing, (2) after chemical and structural homogenization with a thermal calcination step, and (3) in the spinodal decomposed state following a subsequent annealing treatment within the Co-ferrite miscibility gap. Of note is the formation of a wasp-waisted hysteresis loop which emerges for the spinodal decomposed Co-ferrite sample, indicative of more complex magnetization reversal processes at relatively large applied fields than for homogeneous Co-ferrite samples of similar particle size and identical nominal chemistry. First order reversal curve (FORC) analysis is applied to further characterize the magnetization response, and a conventional interpretation of observed features in the FORC contrast is presented to discuss potential dominant magnetization mechanisms. The work described here represents the first application of FORC to spinodal decomposed magnetic ceramics and provides a strong foundation for future investigations seeking to quantitatively describe the impacts of nm-scale chemical, structural, and magnetic fluctuations on magnetization processes in ferrite spinel nanocomposite systems.

Over the last three decades, fiber optic sensors (FOS) have gained a lot of attention for their wide range of monitoring applications across many industries, including aerospace, defense, security, civil engineering, and energy. FOS technologies hold great promise to form the backbone for next‐generation intelligent sensing platforms that offer long‐distance, high‐accuracy, distributed measurement capabilities and multiparametric monitoring with resilience to harsh environmental conditions. The major limitations posed by FOS are 1) cross‐sensitivity, 2) enormous volume and large data generation, 3) low data processing speed, 4) degradation of signal‐to‐noise ratio over the fiber length, and 5) overall cost of sensor and interrogator systems. These challenges can be overcome by building advanced data analytics engines enabled by recent breakthroughs in machine learning (ML) and artificial intelligence (AI). This article presents a comprehensive review of recent studies that integrate ML and AI algorithms with FOS technologies. This review also highlights several FOS technology development directions that promise a significant impact on widespread use for several industrial applications, with an emphasis on energy systems monitoring. A perspective on future directions for further research development is also provided.

We have investigated laser-patterning and devitrification as a novel method to realize emergent properties in modified regions at the ribbon surface consisting of periodic localized laser spots thermally treated under rapid heating and cooling conditions. Fe-based amorphous ribbons were annealed for systematically varied laser power. Extremely high heating and cooling rates on the order of 108-1010K/s have been estimated by finite element analysis simulations. Observations suggest surface melting followed by rapid solidification fast enough to quench and form an amorphous structure upon cooling. Diffusion of heat occurs from the laser irradiated surface region so that a finite volume of material surrounding this region rises in temperature above the crystallization temperature relevant for conventional isothermal annealing experiments. The underlying mechanism of laser annealing and consequences of heat transients involved are discussed in terms of impacts upon micro/nanostructure, residual stresses, and magnetic domain structure surrounding the laser irradiated region. The study illustrates the potential to exploit spatially optimized phase transformations in a scalable manufacturing process of amorphous and nanocrystalline alloys to locally access otherwise inaccessible extreme heating and cooling rates.