An ecofriendly, low-cost, one-pot solvothermal approach has been developed to prepare spherical magnetite nanoparticles with sizes in the 7−12 nm range capped with a dialkylamine. Iron isopropoxide, water vapor, absolute ethanol, oleic acid, and oleylamine were used as iron oxide precursor, hydrolysis agent, solvent and surfactants, respectively. The surfactants' role was investigated and an accurate correlation among the synthetic parameters, the crystallographic phases, and both crystallite and particle size was found. The amounts of oleylamine and oleic acid and the temperature have been revealed to be the key parameters in order to tune particle size and their polydispersity. An in-depth study on the role of each surfactant has pointed out the fundamental role of the amine as a reduction promoter as demonstrated by using different amines and confirmed by Mossbauer measurements. A dual 1 H NMR-Fourier transform infrared spectroscopy approach on selected experiments for the investigation of the capping agents (in the presence of a magnetic phase (Magnetite) or a diamagnetic one (Anatase) prepared in the same synthetic conditions) has been found to be fundamental to clarify the actual nature of the capping agent of the nanoparticles and the reactions involved between the surfactants. New insights on the reaction mechanism confirm the formation of an amide that represents a new cosurfactant for the size and shape regulation and a biocompatible molecular coating of magnetite and anatase nanoparticles.

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We prepared multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at TC=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near TC. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D3d5 hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T.

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