Size controlled cyano-bridged coordination polymer nanoparticles Mⁿ⁺/[M′(CN)_m]^{3 −} (where Mⁿ⁺ = Ni²⁺, Fe²⁺, Co²⁺ and M′ = Fe³⁺, Co³⁺(m = 6); Mo⁵⁺ (m = 8)) have been synthesised and organised by using mesostructured hybrid silica hosts of various sizes (3.4, 5.3 and 7.5 nm) containing –(CH₂)₂C₅H₄N groups. The obtained composite materials were studied by transmission electronic microscopy (TEM), infrared and electronic spectroscopies, nitrogen sorption, X-ray diffraction and magnetic measurements. These analyses reveal the formation of hetero- or homo-metallic cyano-bridged nanoparticles with controlled stoichiometry uniform in size and shape within the silica matrix. The size of the nanoparticles is controlled by the pore size of the silica used. The magnetic study of these nanocomposite materials reveal an appearance of a spin-glass like regime which can be caused by a spin frustration on the surface of the nanoparticles and/or by interparticle magnetostatic interactions.

Ferromagnetic resonance (FMR) and microwave magnetoabsorption can be expected to be powerful tools for characterization of magnetic nanoparticles. In the present work, we have studied the FMR and magnetic field dependence of nonresonant microwave losses in CoNi nanoparticles of about 45, 100, and $200\mathrm{nm}$ caliper sizes prepared by the polyol technique. Contrary to our expectation, FMR lines, although wide, show that the particles are not truly spherical. Subsequent scanning and transmission electron microscopy investigations have confirmed this finding. Further, as before, all the powders are found to have large zero field absorption which reduces on application of a direct current (dc) field parallel to the microwave magnetic field but is relatively insensitive to a dc field if the powder is located in the microwave electric field, hence defining a magnetoimpedance for the system.