Monodisperse ternary ferrite (MFe2O4, M = Co, Ni, Mn, and Fe) nanocrystals have been synthesized through a facile and general route involving thermolysis of an intimately mixed binary metal−oleate complex with similar decomposition temperature of the constituents.

Frequency and magnetic field dependent dielectric measurements have been performed on epitaxial thin films of the double perovskite La 2 NiMnO 6 , revealing a dielectric relaxation and magnetodielectric effect. The films are grown on Nb-doped and SrRuO 3-coated SrTiO 3 substrates using the pulsed laser deposition technique. While a rapid dielectric relaxation is observed at ϳ300 K, the relaxation rate increases dramatically at lower temperatures. Below the Curie temperature of La 2 NiMnO 6 , the dielectric constant increases in a magnetic field for a range of temperature. This temperature range depends on magnetic field and measurement frequency. The results are explained by the influence of a magnetic field on the dipolar relaxation.

The formation mechanism and shape control of monodisperse magnetic cobalt ferrite (CoFe 2 O 4 ) nanocrystals produced by thermolysis of a stoichiometric Co 2+ Fe 2 3+-oleate complex in organic solution has been investigated. Synthesis of the pure ternary CoFe 2 O 4 inverse spinel phase, without formation of any intermediate binary cobalt and iron oxides, is favored by the close thermal decomposition temperature of the Co 2+ -oleate and Fe 3+ -oleate precursors. For reaction temperatures between 250 and 320 °C, the nucleation and growth dynamics dictate the size and shape evolution of the nanocrystals. Prenucleation of CoFe 2 O 4 occurs at 250-300 °C but without any growth of nanocrystals, because the monomer concentration is lower than the critical nucleation concentration. For temperatures in the range of 300-320 °C, which is above the thermolysis temperature of the mixed Co 2+ Fe 2 3+ -oleate complex, the monomer concentration increases rapidly resulting in homogeneous nucleation. Atomic clusters of CoFe 2 O 4 with size <2 nm are initially formed at 314 °C that then grow rapidly when the temperature is raised to 320 °C in less than a minute. The shape of the CoFe 2 O 4 nanocrystals can be reproducibly controlled by prolonging the aging time at 320 °C, evolving from initial spherical, to spherical-to-cubic, cubic, corner-grown cubic, or starlike shapes. Thus, with careful choice of reaction parameters, such as the precursor concentration and the heating rate, it is possible to achieve large-scale synthesis of shape-controlled monodisperse CoFe 2 O 4 nanocrystals with high yield.

The structural and magnetic properties of a series of superlattices consisting of two ferromagnetic metals La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) grown on (001) oriented SrTiO3 are studied. Superlattices with a fixed LSMO layer thickness of 20unit cells and varying SRO layer thickness show a sudden drop in magnetization on cooling through a temperature where both LSMO and SRO layers are ferromagnetic. This behavior suggests an antiferromagnetic coupling between the layers. In addition, the samples having thinner SRO layers (n&lt;6) exhibit enhanced saturation magnetization at 10K. These observations are attributed to the possible modification in the stereochemistry of the Ru and Mn ions in the interfacial region.