Тип публикации: статья из журнала
Год издания: 2015
Идентификатор DOI: 10.1063/1.4936838
Ключевые слова: Anisotropy, Crystallography, High resolution electron microscopy, Magnetic anisotropy, Magnetic properties, Magnetic resonance measurement, Magnetic variables measurement, Magnetism, Mossbauer spectroscopy, Nanomagnetics, Nanoparticles, Particle size, Comparative analysis, Crystallographic position, Ferromagnetic resonance spectroscopy, Magnetic anisotropy constant, Magnetic properties of nanoparticle, Magnetically ordered state, Paramagnetic contribution, Superparamagnetic behavior, Magnetic bubbles
Аннотация: We report the results of comparative analysis of magnetic properties of the systems based on epsilon-Fe2O3, nanoparticles with different average sizes (from similar to 3 to 9 nm) and dispersions. The experimental data for nanoparticles higher than 6-8 nm in size are consistent with the available data, specifically, the transition to the magnetically ordered state occurs at a temperature of similar to 500K and the anomalies of magnetic properties observed in the range of 80-150K correspond to the magnetic transition. At the same time, M} ossbauer and ferromagnetic resonance spectroscopy data as well as the results of static magnetic measurements show that at room temperature all the investigated samples contain epsilon-Fe2O3 particles that exhibit the superparamagnetic behavior. It was established that the magnetic properties of nanoparticles significantly change with a decrease in their size to similar to 6 nm. According to high-resolution electron microscopy and M} ossbauer spectroscopy data, the particle structure can be attributed to the e-modification of trivalent iron oxide; meanwhile, the temperature of the magnetic order onset in these particles is increased, the well-known magnetic transition in the range of 80-150K does not occur, the crystallographic magnetic anisotropy constant is significantly reduced, and the surface magnetic anisotropy plays a decisive role. This is apparently due to redistribution of cations over crystallographic positions with decreasing particle size, which was established using Mossbauer spectra. As the particle size is decreased and the fraction of surface atoms is increased, the contribution of an additional magnetic subsystem formed in a shell of particles smaller than similar to 4 nm becomes significant, which manifests itself in the static magnetic measurements as paramagnetic contribution. (C) 2015 AIP Publishing LLC.
Журнал: JOURNAL OF APPLIED PHYSICS
Выпуск журнала: Vol. 118, Is. 21
ISSN журнала: 00218979
Место издания: MELVILLE
Издатель: AMER INST PHYSICS
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