The elusive ε-Fe2O3 has been obtained as nanoparticles by vacuum heat treatment of yttrium iron garnet in a silica matrix at 300 °C followed by annealing at 1000 °C for up to 10 h in air and employing formamide as a gel modifier. Its nuclear structure is temperature independent as observed from the neutron powder diffraction patterns and has been modeled by the published structures on analogous MM‘O3 compounds. It displays complex magnetic properties that are characterized by two transitions:  one at 480 K from a paramagnet (P) to canted antiferromagnet (CAF1) and the second at ca. 110 K from the canted antiferromagnet (CAF1) to another canted antiferromagnet (CAF2) that has a smaller resultant magnetic moment (i.e., smaller canting angle). The latter transition resembles that of Morin for α-Fe2O3 at 260 K. The magnetization shows unusual history dependence:  it has a bifurcation below 100 K if the field is applied at low temperatures after zero-field-cooled, whereas the bifurcation is above 150 K if the field is applied at high temperatures. The magnetic hardness first increases slightly from 300 to 200 K, then it drastically decreases to zero at 100 K and follows a further increase down to 2 K. The coercive field reaches an unexpected and quite exceptional 22 kOe at 200 K. There appears to be a further ill-defined metamagnetic transition below 50 K, characterized by a doubling of the measured magnetization in 50 kOe. The AF1−AF2 transition is accompanied by sharp peaks in both the real and imaginary components of the ac-susceptibility due to the hard−soft effect, and their peak maxima shift to lower temperatures on increasing the frequency. Mössbauer spectra are characterized by a change in hyperfine field of the tetrahedral Fe by ca. 40% around the transition, suggesting a change of geometry.

Cobalt ferrite, CoFe 2 O 4 , nanoparticles have been obtained from pre-prepared layered double hydroxide carbonate, LDH-CO 3 , by mechanical milling. X-ray powder diffraction shows the only product of the milling for 5 h of the LDH-CO 3 is cobalt ferrite nanoparticles. Longerterm milling induces particle growth characterized by sharpening of the Bragg peaks and an increase of the blocking temperature, while prolonged milling results in the formation of some cobalt metal. Mo ¨ssbauer spectra and temperature dependence of the magnetization of the 5-h milled sample suggest that it consists of nanoparticles of size less than 10 nm with blocking temperature of 200 K, in good agreement with microscopy showing an average size of 6 nm. The magnetic properties exhibit a strong dependence on the particle size as a result of an unusual cation distribution and of surface effect. The saturation magnetization at 5 K and the squareness of the hysteresis loops increase with the average particle size. The difference between zero-field-cooled and field-cooled hysteresis loops is correlated with the presence of randomness of the moments at the surface.

The sonochemical synthesis of stable palladium nanoparticles has been achieved by ultrasonic irradiation of palladium(II) nitrate solution. The starting solutions were prepared by the addition of different concentrations of palladium(II) nitrate in ethylene glycol and poly(vinylpyrrolidone) (PVP). The resulting mixtures were irradiated with ultrasonic 50 kHz waves in a glass vessel for 180 min. The UV-visible absorption spectroscopy and pH measurements revealed that the reduction of Pd(II) to metallic Pd has been successfully achieved and that the obtained suspensions have a long shelf life. The protective effect of PVP was studied using Fourier transform infrared (FT-IR) spectroscopy. It has been found that, in the presence of ethylene glycol, the stabilization of the nanoparticles results from the adsorption of the PVP chain on the palladium particle surface via the coordination of the PVP carbonyl group to the palladium atoms. The effect of the initial Pd(II) concentration on the Pd nanoparticle morphology has been investigated by transmission electron microscopy. It has been shown that the increase of the Pd(II)/PVP molar ratio from 0.13 x 10(-3) to 0.53 x 10(-3) decreases the number of palladium nanoparticles with a slight increase in particle size. For the highest Pd(II)/PVP value, 0.53 x 10(-3), the reduction reaction leads to the unexpected smallest nanoparticles in the form of aggregates.

Small oxidized silicon nanocrystals of average sizes below 3.5 nm are prepared using modified electrochemical etching of a silicon wafer. Modifications introduced in the etching procedure together with postetching treatment in H2O2 lead to a decrease in the nanocrystalline core size and also, to some extent, to changes in the surface oxide. The interplay between these two factors allows us to blueshift the photoluminescence (PL) spectrum from 680 down to 590 nm, which is accompanied by changes in PL dynamics. This continual development, however, stops at about 590 nm, below which abrupt switching to fast decaying blue emission band at about 430 nm was observed. Discontinuity of the spectral shift and possible relation between both bands are discussed.