We report on the M\"ossbauer spectra and magnetization properties of single-crystalline (BiFeO3)x-(BaTiO3)1$-${}x solid solution nanostructures in the form of nanocubes, measuring approximately 150 to 200 nm on a side, prepared by a molten salt solid-state reaction method in the compositional range wherein 0.5$\le${}x$\le${}1. Powder x-ray diffraction (XRD) and monochromatic synchrotron XRD studies indicate products of high purity, which undergo gradual, well-controlled structural transformations from rhombohedral to tetragonal structures with decreasing ``x.'' For all solid solution products, room-temperature magnetization studies exhibit hysteretic behavior with remnant magnetization values of Mr$\ge${}0.32$\hskip0.3em${}emu/g, indicating that the latent magnetization locked within the toroidal spin structure of BiFeO3 has been released. Room-temperature M\"ossbauer spectra show composition-dependent characteristics with decreasing magnetic hyperfine field values and increasing absorption linewidths due to a decrease in the magnetic exchange interaction strength with decreasing x. For the lowest x=0.5 composition studied, the M\"ossbauer spectra show paramagnetic behavior, indicating a N\'eel temperature for this composition below 300 K. However, room-temperature magnetization studies with applied fields of up to 50 kOe show hysteretic behavior for all compositions, including the x=0.5 composition, presumably due to field-induced ordering. Furthermore, hysteresis loops for all compositions exhibit smaller coercivities at 10 K than at 300 K, an observation that may suggest the presence of magnetoelectric coupling in these systems.

Magnetic and Mössbauer measurements are reported on single-crystalline monodispersed $\gamma {\text{-Fe}}_2{\text{O}}_3$ nanoparticles of 12.5 nm diameter, coated with multiple silica and mesoporous silica layers of various thicknesses. The high crystallinity and monodispersity of the samples allow resolution of the tetrahedral (A) and octahedral [B] iron sites of the spinel structure of maghemite. The precisely tuned silica coating thickness offers controlled, homogeneous magnetic dilution with the sample magnetic volume fraction ranging from 1 to 0.002, leading to various degrees of interparticle dipole-dipole interaction strength. Analysis of the zero-field-cooled magnetization data shows that dipole-dipole interactions increase the superparamagnetic energy barrier. The relevant magnetic parameters, for both the individual particles $\left(K_{\text{eff}}\right)$ and the particle assemblies $\left(U_{\text{int}}\right)$, are determined within the framework of weak and strong dipolar-interaction models. At low temperatures, the steepness of the magnetic hyperfine field reduction with increasing temperature in the strongly interacting particle assemblies is examined within the context of the collective magnetic-excitations model.

Reduced nitrogen oxide ligands such as NO⁻/HNO or nitroxyl participate in chemistry distinct from nitric oxide (NO). Nitroxyl has been proposed to form at heme centers to generate the Enemark–Feltham designated {FeNO}⁸ system. The synthesis of a thermally stable {FeNO}⁸ species namely, [Co(Cp*)₂][Fe(LN₄)(NO)] (3), housed in a heme-like ligand platform has been achieved by reduction of the corresponding {FeNO}⁷ complex, [Fe(LN₄)(NO)] (1), with decamethylcobaltocene [Co(Cp*)₂] in toluene. This complex readily reacts with metMb, resulting in formation of MbNO via reductive nitrosylation by the coordinated HNO/NO⁻, which can be inhibited with GSH. These results suggest that 3 could serve as a potential HNO therapeutic. Spectroscopic, theoretical, and structural comparisons are made to 1 and the {CoNO}⁸ complex, [Co(LN₄)(NO)] (2), an isoelectronic analogue of 3.

Comparative studies are presented of iron oxide nanoparticles in the 7–15 nm average diameter range ball milled in hexane in the presence of oleic acid. Transmission electron microscopy identified spherical particles of decreasing size as milling time and/or surfactant concentration increased. Micromagnetic characterization via Mössbauer spectroscopy at room temperature yielded broadened magnetic spectroscopic signatures, while macromagnetic characterization via vibrating sample magnetometry of 7-8 nm diameter particles showed largely superparamagnetic behavior at room temperature and hysteretic at 2 K. Zero-field and field-cooled magnetization curves exhibited a broad maximum at ~215 K indicating the presence of strong interparticle magnetic interactions. The specific absorption rates of ferrofluids based on these nanoparticle preparations were measured in order to test their efficacies as hyperthermia agents.

Highly stable CeFeO _x thin films that can undergo a reversible fluorite to perovskite phase transition were synthesized.