V. Sandu, E. Cimpoiasu, S. Greculeasa, A. Kuncser, M.S. Nicolescu, V. Kuncser
U.S. Naval Academy,
Keywords: magnetite, glass ceramics, Mössbauer spectroscopy, AC susceptibility, magnetic relaxation, superparamagnetism
Summary:We investigated the specific magnetic structure and magnetic relaxation phenomena in magnetite nano-entities grown in a glassy matrix by controlled crystallization of Fe-containing borosilicate and boroaluminosilicate glasses in the presence of two types of nucleating agents, Cr2O3 and P2O5. We found that the structure, morphology and magnetic properties are strongly influenced by the nucleating agents. Cr2O3 generates magnetite-based glass ceramics with magnetite configurations showing an upward relaxation of magnetization at low and high temperatures but downward at intermediate temperatures. The magnetite grown with P2O5 displays only downward relaxation but with different signs of the temperature derivative of the relaxation rate S in different temperature ranges. The observed effects  are discussed with respect to the following factors: i) the existence of a multimodal size distribution of the magnetite (nano)particles as revealed by high resolution electron microscopy; ii) the degree of occupation of different sublattices of the magnetite structure with Fe3+ and Fe2+ ions; and iii) the interplay between the relaxation mechanisms in different temperature ranges. Acknowledgments: This work was supported by the Romanian Ministry of Education, Executive Unit for Funding High Education, Research, Development and Innovation under the Idea-Complex Research Grant PN-II-ID-PCCE-2011-2-0006 (contract #3/2012), Core Program PN 45N, and by the Office of Naval Research at USNA . “Magnetite-based glass-ceramics prepared by controlled crystallization of borosilicate glasses: Effect of nucleating agents on magnetic properties and relaxation”, V. Sandu, E. Cimpoiasu, S. Greculeasa, A. Kuncser, M. S. Nicolescu, and V. Kuncser, Ceramics International (2016) http://dx.doi.org/10.1016/j.ceramint.2016.11.188.