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

► The samples contain agglomerates of amorphous SiO2 particles 10-20 nm in size. ► Small crystalline Mn-rich NPs (3-10 nm) and aggregates of the small NPs were observed. ► Dominant magnetic phase in the Mn-rich NPs at higher temperatures is λ-MnO2. ► Below TC=43 K strong FiM of the minor Mn3O4 phase masks the weak AFM of λ-MnO2. ► Magnetic moments of the small Mn3O4 NPs are exposed to blocking process below TC.