Formation and evolution of magnetic nanoparticles in borate glass simultaneously doped with Fe and Mn oxides

Abstract

Evolution of the phase state of paramagnetic additions at various stages of synthesis and subsequent thermal treatment of glasses of the system Al 2 O 3-K 2 O-B 2 O 3 simultaneously doped with Fe 2 O 3 and MnO is studied by means of a combination of experimental techniques: Faraday rotation ͑FR͒, electron magnetic resonance ͑EMR͒, transmission electron microscopy ͑TEM͒, Mössbauer spectroscopy, and magnetic measurements. Both FR and EMR show that magnetically ordered clusters occur already at the first stage of the glass preparation. In particular, for the ratio of the Fe and Mn oxides in the charge close to 3:2, fine magnetic nanoparticles are formed with characteristics similar to those of manganese ferrite. By computer simulating the EMR spectra at variable temperatures, a superparamagnetic nature of these nanoparticles is confirmed and their mean diameter is estimated as approximately 3.2 nm. In the thermally treated glasses larger magnetic nanoparticles are formed, giving rise to FR spectra, characteristic of magnetically ordered systems, and the EMR spectra different from those in as-prepared glasses but also showing superparamagnetic narrowing. The Mössbauer spectroscopy corroborates the manganese ferrite structure of the nanoparticles and indicates their coexistence in the ferrimagnetic and superparamagnetic states. The TEM shows the presence of polydisperse nanoparticles on the background of the glass matrix, and electron diffraction of a selected region containing larger particles indicates a crystal structure close to that of MnFe 2 O 4. Energy-dispersive atomic x-ray spectra confirm that the major part of Fe and Mn introduced to the glass composition is gathered in the particles, with the concentration ratio close to 2:1, characteristic of bulk MnFe 2 O 4. Magnetic hysteresis loops of samples subjected to an additional thermal treatment demonstrate a strong increase in the coercive force, remnant magnetization, and high-field magnetic susceptibility with temperature decrease. The consistent results obtained using various techniques demonstrate that the formation of nanoparticles with characteristics close to those of MnFe 2 O 4 confers to these glasses magnetic and magneto-optical properties typical of substances possessing magnetic order.

Electron magnetic resonance and magnetooptical studies of nanoparticle-containing borate glasses

“…However, such behaviour is observed only for diluted and not for exchange-coupled paramagnetic ions; indeed, clustering and nanoparticle formation cause deviations from this simple picture, as was demonstrated in Ref. [4].…”

“…These glasses, usually after an additional thermal treatment, acquire a non-linear magnetic field dependence of the magnetization with hysteresis and magnetic saturation. At the same time, they retain a high transparency in a part of the visible and near infrared spectral range and demonstrate a high value of magneto-optical Faraday rotation (FR) [3,4]. Meanwhile, the FR values and their spectral characteristics in these glasses largely depend on thermal treatment conditions as well as on absolute and relative dopant concentrations.…”

Formation, characterization and magnetic properties of maghemite γ-Fe2O3 nanoparticles in borate glasses

“…[7]. Prior to the synthesis, Fe 2 O 3 and co-doping element oxides, i.e., Y 2 O 3 , Bi 2 O 3 , PbO, Sm 2 O 3 in different combinations were loaded in the charge in respective concentrations of ca.…”

“…percentage Fe 2 O 3 [4,5] or maghemite γ-Fe 2 O 3 nanoparticles in silica-gel glasses [6] were identified by electron magnetic resonance (EMR). In potassiumalumina-borate glasses co-doped with iron and manganese or with iron and cobalt, nanoparticles of manganese or cobalt ferrite, correspondingly, were detected with different techniques [7,8] starting from 1.5 wt. percentage of Fe 2 O 3 and 1.0 wt.…”

Synthesis, structure and spectral properties of potassium-alumina-borate glass with nanocrystals of manganese ferrite

“…В ряде работ (например, [8,9] [10,11] было показано, что стекла, содержащие в качестве парамагнитных примесей оксид железа Fe 2 O 3 и оксид марганца MnO, демонстрируют чрезвычайно силь-ный отклик магнитооптических свойств материала на набор технологических факторов, а также в стек-лах этой группы достигаются большие значения ФВ в диапазоне 1,3-1,5 мкм.…”