Magnetic properties of Mn-oxide nanoparticles dispersed in an amorphous SiO2 matrix

摘要: Abstract Samples of Mn-oxide nanoparticles dispersed in an amorphous SiO2 matrix with manganese concentration 0.7 and 3 at% have been synthesized by a sol–gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates silica particles 10–20 nm size. In two types Mn-rich are dispersed, smaller dimensions between 3 10 nm, larger crystalline areas consisting aggregates nanoparticles. High-temperature magnetic susceptibility study reveals dominant phase at higher temperatures is λ-MnO2. At below TC=43 K strong ferrimagnetism originating from minor Mn3O4 masks relatively weak magnetism λ-MnO2 antiferromagnetic interactions. Magnetic field dependence maximum zero-field-cooled magnetization for both vicinity 40 K, frequency shift real component ac sample Mn suggest moments 10 nm exposed to thermally activated blocking process just Curie temperature TC. Appearance 10 K indicates possible spin glass freezing low which might occur geometrically frustrated sublattice crystal structure.