Magnetic Properties of Mn-Doped Amorphous SiO2 Matrix
D. Milivojević a, B. Babić-Stojića, V. Jokanović a, Z. Jagličić b and D. Makovec c
aVinča Institute of Nuclear Sciences, University of Belgrade, P.O.Box 522, 11001 Belgrade, Serbia
bInstitute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana, Slovenia
cJožef Stefan Institute, Department for Materials Synthesis, Jamova 39, 1000 Ljubljana, Slovenia
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Samples of Mn-doped amorphous SiO2 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-MnO2. At temperatures below TC=43 K strong ferrimagnetism originating from the minor Mn3O4 phase masks the relatively weak magnetism of λ-MnO2. 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 Mn3O4 nanoparticles with dimensions below 10 nm are subject to thermally activated blocking process just below the Curie temperature TC. 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-MnO2 crystal structure.
DOI: 10.12693/APhysPolA.120.316
PACS numbers: 75.50.Lk, 75.47.Lx, 75.50.Tt