Microwave and magneto-optic properties of ε-Fe2O3 nanoparticles arising in borate glasses doped with Fe and Gd

The ε-Fe2O3 nanoparticles in borate glasses co-doped with low concentrations of Fe2O3 and Gd2O3 were investigated with two experimental techniques – visible magnetic circular dichroism (MCD) and electron spin resonance (ESR). The most prominent features of the MCD spectra are: non-linear dependence of the spectral maxima intensities on the Gd concentration and strong increase with the temperature decrease. The ESR spectra of these glasses exhibit two features with g = 4.3 due to the diluted Fe3+ ions and 2.0 associated both with Fe3+ ions and with nanoparticles. The integrated spectra intensities do not follow the T-1 Curie law suggesting a considerable contribution from the magnetically ordered nanoparticles to ESR. Analysis of the MCD and ESR concentration dependences allow suggestion on the Gd ions incorporation into nanoparticles

Microwave and magneto-optic properties of ε-Fe

The ε-Fe2O3 nanoparticles in borate glasses co-doped with low concentrations of Fe2O3 and Gd2O3 were investigated with two experimental techniques – visible magnetic circular dichroism (MCD) and electron spin resonance (ESR). The most prominent features of the MCD spectra are: non-linear dependence of the spectral maxima intensities on the Gd concentration and strong increase with the temperature decrease. The ESR spectra of these glasses exhibit two features with g = 4.3 due to the diluted Fe3+ ions and 2.0 associated both with Fe3+ ions and with nanoparticles. The integrated spectra intensities do not follow the T-1 Curie law suggesting a considerable contribution from the magnetically ordered nanoparticles to ESR. Analysis of the MCD and ESR concentration dependences allow suggestion on the Gd ions incorporation into nanoparticles

Microwave and magneto-optic properties of ε-Fe2O3 nanoparticles arising in borate glasses doped with Fe and Gd

The ε-Fe2O3 nanoparticles in borate glasses co-doped with low concentrations of Fe2O3 and Gd2O3 were investigated with two experimental techniques – visible magnetic circular dichroism (MCD) and electron spin resonance (ESR). The most prominent features of the MCD spectra are: non-linear dependence of the spectral maxima intensities on the Gd concentration and strong increase with the temperature decrease. The ESR spectra of these glasses exhibit two features with g = 4.3 due to the diluted Fe3+ ions and 2.0 associated both with Fe3+ ions and with nanoparticles. The integrated spectra intensities do not follow the T-1 Curie law suggesting a considerable contribution from the magnetically ordered nanoparticles to ESR. Analysis of the MCD and ESR concentration dependences allow suggestion on the Gd ions incorporation into nanoparticles

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

We report electron magnetic resonance (EMR) and magnetooptical studies of borate glasses of molar composition 22.5K2O-22.5Al2O3-55B2O3 co-doped with low concentrations of Fe2O3 and MnO. In as-prepared samples the paramagnetic ions, as a rule, are in diluted state. However, in the case where the ratio of the iron and manganese oxides in the charge is 3/2, magnetic nanoparticles with characteristics close to those of manganese ferrite are formed already at the first stage of the glass preparation, as evidenced by both magnetic circular dichroism (MCD) and EMR. After thermal treatment all glasses show characteristic MCD and EMR spectra, attesting to the presence of magnetic nanoparticles, predominantly including iron ions. Preliminary EXAFS measurements at the FeK-absorption edge show an emergence of nanoparticles with a structure close to MnFe2O4 after annealing the glasses at 560 1C. By computer simulating the EMR spectra at variable temperatures, a superparamagnetic nature of relatively broad size and shape distribution with the average diameter of ca. 3-4 nm. The characteristic temperature-dependent shift of the apparent resonance field is explained by a strong temperature dependence of the magnetic anisotropy in the nanoparticles. The formation of magnetic nanoparticles confers to the potassium-alumina-borate glassesmagnetic and magneto-optical properties typical of magnetically ordered substances. At the same time, they remain transparent in a part of the visible and near infrared spectral range and display a high Faraday rotation value

Effect of gadolinium on magnetic circular dichroism and electron magnetic resonance of ε-Fe2O3 nanoparticles formed in borate glasses

A remarkable characteristic of borate glasses is the ability of forming magnetic nanoparticles at low doping with transition element oxides. We have studied structure and magnetic properties of iron oxide nanoparticles formed in borate glasses, in particular, concentration and temperature dependences of magnetic circular dichroism (MCD) and electron magnetic resonance (EMR) spectra. A series of glasses of molar composition 22.5K 2 O-22.5Al 2 O 3-55B 2 O 3 doped with 1.5 mass % of Fe 2 O 3 and different contents of Gd 2 O 3 from 0.1 to 1.0 mass % was prepared using a conventional melt quenching technique and subjected to an additional thermal treatment. The whole set of results allows to identify the predominant magnetic phase in these glasses as ε-Fe 2 O 3 nanoparticles, with a considerable part of iron ions substituted by gadolinium. Analysis and computer simulations of the EMR spectra allow separating the contribution of electron paramagnetic resonance of diluted iron ions and together with the temperature dependences of magnetization demonstrate a superparamagnetic character of the nano-particle magnetism

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

Evolution of the phase state of paramagnetic additions at various stages of synthesis and subsequent thermal treatment of glasses of the system Al2O3-K2O-B2O3 simultaneously doped with Fe2O3 and MnO is studied by means of a combination of experimental techniques: Faraday rotation (FR), electron magnetic resonance (EMR), transmission electron microscopy (TEM), 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 MnFe2O4. 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 MnFe2O4. 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 MnFe2O4 confers to these glasses magnetic and magneto-optical properties typical of substances possessing magnetic order

Сравнительное изучение -Fe2O3 и ϵ-Fe2O3 наночастиц, формирующихся в стекле, допированном железом и гадолинием

Formation and properties of the iron oxides -Fe2O3 and ϵ-Fe2O3 nanoparticles arising in glasses of basic compositions Ge2O-K2O-Al2O3-B2O3 and K2O-Al2O3-B2O3 doped with different concentrations of Fe2O3 and Gd2O3 and subjected to the additional thermal treatment are studied. The X-ray diffraction, TEM microscopy, magnetooptical effects, and electron spin resonance study allow elucidating the matrix and Gd role in determining the nanoparticle propertiesИзучены свойства наночастиц -Fe2O3 и ϵ-Fe2O3, формирующихся в стеклах основного состава Ge2O-K2O-Al2O3-B2O3 и K2O-Al2O3-B2O3, допированных Fe2O3 и Gd2O3 и подвергнутых дополни- тельной термической обработке. Результаты исследования рентгеновской дифракции, электрон- ной микроскопии, магнитооптических эффектов и электронного спинового резонанса позволили объяснить роль матрицы и гадолиния в определении свойств наночасти

Сравнительное изучение -Fe2O3 и ϵ-Fe2O3 наночастиц, формирующихся в стекле, допированном железом и гадолинием

Formation and properties of the iron oxides -Fe2O3 and ϵ-Fe2O3 nanoparticles arising in glasses of basic compositions Ge2O-K2O-Al2O3-B2O3 and K2O-Al2O3-B2O3 doped with different concentrations of Fe2O3 and Gd2O3 and subjected to the additional thermal treatment are studied. The X-ray diffraction, TEM microscopy, magnetooptical effects, and electron spin resonance study allow elucidating the matrix and Gd role in determining the nanoparticle propertiesИзучены свойства наночастиц -Fe2O3 и ϵ-Fe2O3, формирующихся в стеклах основного состава Ge2O-K2O-Al2O3-B2O3 и K2O-Al2O3-B2O3, допированных Fe2O3 и Gd2O3 и подвергнутых дополни- тельной термической обработке. Результаты исследования рентгеновской дифракции, электрон- ной микроскопии, магнитооптических эффектов и электронного спинового резонанса позволили объяснить роль матрицы и гадолиния в определении свойств наночасти

Unusual magnetic phase transitions in Gd3+ clusters in multicomponent oxide glasses

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Nanoparticle-containing glasses co-doped with transition and rare earth elements: Comparative studies of transparent magnets

A comparative multitechnique study (including transmission electron microscopy, synchrotron radiation, static magnetisation, magnetic circular dichroism and electron magnetic resonance) has been carried out of nanoparticle-containing borate glasses of two different types: (i) with iron and manganese oxide additives and (ii) with iron and rare earth oxide additives. Due to the presence of magnetic nanoparticles, these glasses have a nonlinear magnetic field dependence of magnetization with hysteresis and saturation while remaining transparent in the visible and near-infrared spectral ranges. The nature of the nanoparticles has been identified as manganese ferrite for type (i) glasses and maghemite for type (ii) glasses. The synchrotron radiation studies as well as the computer-assisted electron magnetic resonance provide an insight into the morphological characteristics of the magnetic nanoparticles in the glass