Monodomain magnetic nanoparticles, due to their size, demonstrate physical properties not seen in the bulk materials, such as size-dependent magnetization reversal fields. They can be also made into a magnetic suspension or ferrofluid. There is thus growing interest in the application of these materials to ferrofluids, spintronics, directed assembly, as well as for imaging and therapeutic applications. In this article, we provide an overview of these materials, discuss the fundamental physical properties, describe several routes for the “bottom-up” generation of these materials, and identify major challenges for the future of these fields. The articles in this issue describe various aspects of the characterization and application of magnetic nanoparticles.

Mesoscale (nanometers to microns) magnetic particles are becoming increasingly important in biomedical applications both in vitro for cell and tissue-based research and in vivo for clinical imaging and therapy. These applications generally rely on the fact that, while the body is relatively transparent to magnetic fields, magnetic particles within the body, or in ex vivo biological samples, will couple strongly to applied external fields. By synthesizing bio-functionalized, biocompatible polymer/magnetic particle composites, this remote coupling provides a mechanism for the precisely targeted actuation of cell signaling pathways, delivery of genes, targeted transmission of thermal energy, generation of tissue matrix, and imaging (via magnetic resonance imaging), among others. This article explores a variety of biomedical applications of mesoscale magnetic particles, some of which are routinely used in the clinic and in biomedical laboratories, with others approaching the realm of science fiction.

When colloidal nanoparticles made of soft magnetic materials have strong interparticle interactions, new magnetic phases may be formed, such as super-ferromagnets or super-spin glasses, with different local temperature and field-dependent magnetization dynamics. Magneto-transport experiments on nanoscale tunnel junctions formed in magnetic nanoparticle arrays, defined either by scanning probe tips or patterned nanoscale electrodes, can be used as probes of the magnetization dynamics.

A novel Ba2MgMoO6:Eu3+ orange-red phosphor was synthesized by the Pechini method and characterized by x-ray diffraction. Photoluminescence properties of BaMgMoO6:Eu3+ phosphors have been represented in the excitation and emission spectra. The charge transfer (CT) band of Ba2MgMoO6 host is situated at near-ultraviolet (UV) region, whose central wave length and bandwidth are 394 and 80 nm, respectively. And it matches well the emission wave length from near-UV light emitting diodes (LEDs). The most intensive emission of 5D0 → 7F1 (598 nm) of Eu3+ in Ba2MgMoO6:Eu3+ is much narrow with a full width at half-maximum less than 2 nm under excitation with either CT band or 394 nm. And a low concentration quenching occurs in Ba2MgMoO6:Eu3+, and the optimal doping concentration is about 0.05. The mechanism of charge and energy transfer from Ba2MgMoO6 host to Eu3+ is proposed and analyzed on the basis of its crystal structure. In a word, Ba2MgMoO6:Eu3+ may be a promising orange-red component for near UV white LEDs.

Isothermal crystallization kinetics of gamma-irradiated syndiotactic polystyrene (sPS) has been investigated by differential scanning calorimetry. Amorphous sPS samples were irradiated in air with gamma ray at various doses from 0 to 800 kGy, at a rate of 30 kGy/h, and melt-crystallized at different temperatures and times. Kinetics parameters were determined using Avrami's model with Gaussian functions and a modified Arrhenius equation. Isothermally crystallized sPS irradiated in air with gamma ray exhibited multiple endothermic melting peaks corresponding to various crystalline forms, and the radiation dose had a strong effect on their melting enthalpies, crystallinities, and crystallization kinetic parameters. The amount of the α-crystalline form increased with increasing crystallization time and those of the β- and β′ forms had an opposite trend. Both crystallization half time and crystallization activation energy of the α form in gamma-irradiated sPS increased with increasing radiation dose.