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Room-Temperature Ferromagnetism in Zn-Mn-O, X-Ray Photoemission Surface Study

100%

Milivojević D., Babić-Stojić B., Blanuša J., Kovač J.

Acta Physica Polonica A

2011

vol. 120

issue 2

311-315

Room temperature ferromagnetic properties of Zn-Mn-O show evident dependence on manganese concentration and preparation conditions. We systematically studied series of samples with manganese concentration ranging from 0 to 10 at.%, prepared in air at thermal treatment temperatures ranging from 400 to 900°C. The samples were investigated by X-ray diffraction, TEM, magnetization measurements and XPS spectroscopy. XPS analyses of surface composition, chemical bonding and XPS depth profiling were successfully employed on powder revealing the chemical composition at the surface of the grains and underneath. The study emphasizes important role of the grain surface in observed room temperature ferromagnetism. It seems that the ferromagnetic phase is correlated with oxygen build up at the surface.

Magnetic Properties of Mn-Doped Amorphous SiO_2 Matrix

88%

Milivojević D., Babić-Stojić B., Jokanović V., Jagličić Z., Makovec D.

Acta Physica Polonica A

2011

vol. 120

issue 2

316-321

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.

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2 Acta Physica Polonica A

2 2011

2 Babić-Stojić B.

2 Milivojević D.

1 Blanuša J.

1 Jagličić Z.

1 Jokanović V.

1 Kovač J.

1 Makovec D.

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Room-Temperature Ferromagnetism in Zn-Mn-O, X-Ray Photoemission Surface Study

Magnetic Properties of Mn-Doped Amorphous SiO_2 Matrix