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Disordered and frustrated magnetization of different surface coated (Cr2O3, Co3O4, ZrO2, and SiO2) MnFe2O4 nanoparticles have been studied using SQUID-magnetometry. Magnetic measurements, such as ZFC/FC and ac-susceptibility evidence surface spin-glass behavior. ZFC/FC curves were also compared with numerical simulation to get information about effective anisotropy constants. Frequency dependent ac susceptibility results were analyzed by using Arrhenius, Vogel Fulcher and dynamic scaling laws to further confirm the spin-glass behavior. It is observed that the strength of surface spins disorder and frustration strongly depends upon the type of the coating material. All these analyses signify that disordered and frustrated surface magnetization in MnFe2O4 nanoparticles greatly depend on the type of the surface coating materials and are useful for controlling the nanoparticle’s magnetism for different practical applications.

The structure of nano-crystalline Fe₂O₃ particles, synthesized using the microwave plasma technique, has been analysed using synchrotron based X-ray absorption spectroscopy and X-ray powder diffraction, as well as transmission electron microscopy. Furthermore, magnetic properties, the crystal structure, and the microstructures are compared and the potential model character of the samples for structure simulations is discussed.

We describe the synthesis of cerium, thorium and uranium oxide nanoparticles embedded in a mesoporous matrix as template in a kind of nanocasting technique. The solid matrix is used as a template to obtain and stabilize the actinide oxide nanoparticles. We apply high resolution transmission electron microscopy (HR-TEM) to show evidence of metal oxide incorporation into the matrix pores and analyze their structure. Measured interplanar distances and calculated lattice parameters for synthesized nanosized CeO2−x and ThO2 samples differ from their bulk crystalline counterparts. We obtain with our synthesis CeO2−x particles containing both Ce4+ and larger sized Ce3+. The lattice parameter for these ceria nanoparticles is found to be larger than the bulk value due to the presence of Ce3+ with its larger ionic radius. The presence of Ce3+ was established by means of high resolution X-ray emission spectroscopy (HRXES), applied to the investigation of nanoparticles for the first time. The ThO2 nanoparticles exhibit a decrease in interplanar distances, as one might generally expected for these nanoclusters. However, the lattice distance decrease for our particles is remarkable, up to 5%, indicating that contact with the surrounding silica matrix may exert a bond distance shortening effect such as through significant external pressure on the particle surface.

The phase transformations of nanoscaled (n-) Al$_{2}$O$_{3}$-coated and noncoated ZrO$_{2}$ particles synthesized in a microwave plasma have been investigated by perturbed-angular-correlation (PAC) measurements of the electric quadrupole interaction (QI) of $^{181}$Ta on Zr sites between 290 and 1600 K. For the phase identification and structural characterization the QI parameters of the nanoscaled particles are compared to those of coarsegrained ZrO$_{2}$ which were measured between 290 and 2160 K. The PAC spectra of the nanoscaled particles in the as-prepared state are characterized by a broad distribution of strong, axially asymmetric QI’s, which reflects a highly disordered oxygen environment of the Zr sites. Upon annealing, the tetragonal phase is the first well-crystallized structure to emerge at about 500 K, both in coated and noncoated n-ZrO2, in contrast to the previously reported annealing reaction of n-ZrO$_{2}$ synthesized by gas-phase condensation in which the tetragonal phase has not been observed. This disorder-order transformation is partially reversible upon cooling. In n-ZrO$_{2}$ /Al$_{2}$O$_{3}$ synthesized in a microwave plasma the monoclinic phase can be completely suppressed up to 1600 K. In the noncoated particles monoclinic ZrO$_{2}$ starts to appear at 600 K. At 1400 K the transformation from the monoclinic to the tetragonal phase of noncoated n-ZrO2 was observed to occur with a transformation rate of $\lambda$=6.9(1.2)x10$^{-5}$ s$^{-1}$. In nanoscaled coated and noncoated tetragonal ZrO$_{2}$ the T$^{3/2}$-temperature dependence of the quadrupole frequency v$_{q}$ is weaker than in the same phase of the coarse-grained compound, suggesting a decrease of the mean-square vibrational amplitudes with decreasing particle size.