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2011 | 120 | 2 | 316-321
Article title

Magnetic Properties of Mn-Doped Amorphous SiO_2 Matrix

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Samples of Mn-doped amorphous SiO_2 matrix with manganese concentration 0.7 and 3 at.% have been prepared by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10 - 20 nm in size. Two types of Mn-rich particles are dispersed in silica matrix, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility reveals that dominant magnetic phase at higher temperatures is λ-MnO_2. At temperatures below T_{C}=43 K strong ferrimagnetism originating from the minor Mn_3O_4 phase masks the relatively weak magnetism of λ-MnO_2. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the AC magnetic susceptibility in the sample with 3 at.% Mn suggest that the magnetic moments of the smaller Mn_3O_4 nanoparticles with dimensions below 10 nm are subject to thermally activated blocking process just below the Curie temperature T_{C}. The low-temperature maximum in the zero-field-cooled magnetization observed for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments in the geometrically frustrated Mn sublattice of the λ-MnO_2 crystal structure.
Physical description
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