The remarkable multimodal functionalities of magnetic nanoparticles, conferred by their size and morphology, are very important in resolving challenges slowing the progression of nanobiotechnology. The rapid and revolutionary expansion of magnetic nanoparticles in nanobiotechnology, especially in nanomedicine and therapeutics, demands an overview of the current state of the art for synthesizing and characterizing magnetic nanoparticles. In this review, we explain the synthesis routes for tailoring the size, morphology, composition, and magnetic properties of the magnetic nanoparticles. The pros and cons of the most popularly used characterization techniques for determining the aforementioned parameters, with particular focus on nanomedicine and biosensing applications, are discussed. Moreover, we provide numerous biomedical applications and highlight their challenges and requirements that must be met using the magnetic nanoparticles to achieve the most effective outcomes. Finally, we conclude this review by providing an insight towards resolving the persisting challenges and the future directions. This review should be an excellent source of information for beginners in this field who are looking for a groundbreaking start but they have been overwhelmed by the volume of literature.

Passive optical isolators are needed in silicon photonics but unavailable due to challenges in rare-earth iron garnet processing and integration. Material challenges include incompatibility with silicon and high annealing temperatures, and design challenges include a need for polarization diversity and a preference for no external magnetic bias. These challenges have restricted optical isolation to discrete modules that require physical pick and place of bulk garnet pieces. This review presents developments in the processing of magneto-optical garnets on Si and the enhancement of their Faraday rotation that enables small footprint isolators on silicon waveguide structures. For example, seedlayers and/or new garnet compositions have enabled monolithic Si integration, and in some cases, hybrid integration of garnet-on-garnet or transfer-printed garnet nanosheets enable reduced on-chip thermal processing. Integrated isolators that utilize non-reciprocal phase shift (NRPS) or non-reciprocal mode conversion (NRMC) have been demonstrated to have isolation ratios up to 30 dB, insertion loss as low as 9 dB, polarization diversity and magnet-free operation in the desired telecommunication wavelengths. The advances in materials, processing techniques, and isolator designs shown here will pave the way for on-chip isolators and novel multi-lane photonic architectures.

The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are here realized to fill the ‘missing link’ in source-integrated near infrared photonic circuits. The isolators are simple 1D 2-element waveguides, where garnet claddings and longitudinal magnetic fields produce nonreciprocal mode conversion, the waveguide equivalent of Faraday Rotation (FR). Quasi-phase matched claddings are used to overcome the limitations of birefringence. Current experimental SOI isolators use nonreciprocal phase shift (NRPS) in interferometers or ring resonators, but to date NRPS requires TM-modes, so the TE-modes normally produced by integrated lasers cannot be isolated without many ancillary polarisation controls. The presented FR isolators are made via lithography and sputter deposition, which allows facile upscaling compared to the pulsed laser deposition or wafer bonding used in the fabrication of NRPS devices. Here, isolation ratios and losses of 11 dB and 4 dB were obtained, and future designs are identified capable of isolation ratios >30 dB with losses <6 dB.