Nanocomposite materials provide the possibility for multifunctional properties in contrast with their more-limited single-component counterparts. Here, we report the synthesis and characterization of the first all-inorganic core/shell hybrid magnetic-optical nanoparticle, cobalt/cadmium selenide. The core/shell nanocrystals are prepared in a facile one-pot reaction, and their microstructure is analyzed using low- and high-resolution transmission electron microscopy. Using magnetic and optical characterization, we demonstrate bifunctional behavior, whereby the core retains the magnetic properties of the starting Co nanoparticle, and the shell emits similarly to a single-component CdSe nanoparticle. Interestingly, while the coercivity was found to be unchanged by shell formation, the blocking temperature for the composite structure was observed to be substantially lower (Co: >350 K; Co/CdSe: 240 K). In addition, we observed that at low temperatures (20 K) shell CdSe photoluminescence (PL) decay was very rapid (<1 ns). In contrast, nanocrystalline CdSe PL decay is typically much slower at such temperatures (>50 ns). Finally, we propose possible explanations for the unusual magnetic and optical behavior of the core/shell hybrid nanostructures.

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The compounds, Eu14 - x Ca x MnSb11 (x < 3), have been prepared by heating the mixture of stoichiometric amounts of the elements, sealed in a quartz-jacketed Ta tube, in a two-zone furnace with T high = 1100 and T low = 1050 °C for 10 days. These compounds are isostructural with the Zintl compound Ca14AlSb11. The rare-earth transition-metal compounds crystallize in the tetragonal space group I41/acd, Z = 8, T = 90 K, a = 17.2235(7) and c = 22.6555(9) Å, V = 6720.7(5) Å3, and R 1 /wR 2 (0.0413/0.1129) for x = 1.45 and a = 17.1737(7) and c = 22.5741(10) Å, V = 6657.9(5) Å3, and R 1 /wR 2 (0.0392/0.1122) for x = 2.83. Temperature-dependent magnetic susceptibility measurement of the powder samples reveals complex magnetic interactions in the compounds and indicates a canted ferromagnetic configuration for Eu14 - x Ca x MnSb11. As the amount of nonmagnetic Ca increases to x = 2, the effective magnetic moment decreases from 29.9 to 27.9 μB/f.u., and the paramagnetic Curie temperature of the compound increases from 82.4 to 86.4 K at 1000 Oe. The magnetotransport properties of one compound, Eu13CaMnSb11 (x = 1), were measured and show a close relation to its magnetic properties, especially in the low-temperature region. The influence of chemical substitution on the structural and physical properties of Eu14 - x Ca x MnSb11 will be discussed in terms of the site preferences of Ca doping into the four different Eu sites.

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