Oxana Ivanova

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), Mossbauer 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 ma...

Magnetic nanoparticles formed in glasses co-doped with iron and larger radius elements

A new type of nanoparticle-containing glasses based on borate glasses co-doped with low contents of iron and larger radius elements, Dy, Tb, Gd, Ho, Er, Y, and Bi, is studied. Heat treatment of these glasses results in formation of magnetic nanoparticles, radically changing their physical properties. Transmission electron microscopy and synchrotron radiation-based techniques: x-ray diffraction, extended x-ray absorption fine structure, x-ray absorption near-edge structure, and small-angle x-ray scattering, show a broad distribution of nanoparticle sizes with characteristics depending on the treatment regime; a crystalline structure of these nanoparticles is detected in heat treated samples. Magnetic circular dichroism (MCD) studies of samples subjected to heat treatment as well as of maghemite, magnetite, and iron garnet allow to unambiguously assign the nanoparticle structure to maghemite, independently of co-dopant nature and of heat treatment regime used. Different features observed in the MCD spectra ...

Nanostructures Based on Glasses Doped with 3d and 4f Elements

Nano-composite structures based on potassium-aluminum-germanium glasses doped simultaneously with Fe and rare earth (RE) oxides - Gd, Tb, Dy, Ho, or Yb were studied for the first time. Samples were fabricated by glass technology and subjected to an additional thermal treatment at different regimes. Formation of magnetic nanoparticles was revealed with transmission electron microscope. Morphology and space distribution of nanoparticles in the glasses as well as optical and magneto optical spectra have been shown to be dependent on the additional treatment regime and almost independent of the type of the rare earth element.

Ensembles of γ-Fe2O3 Nanoparticles Formed during Devitrification of Borate Glasses

Structural, magnetic and magneto-optical properties of borate glasses co-doped with Fe and the lager radius ions are presented. Maghemite, γ-Fe2O3, nanoparticles arise in the glasses as a result of their thermal treatment in different regimes. Magnetization FC and ZFC temperature dependences demonstrate the superparamagnetic behavior of the particles with the blocking temperature below the room temperature. The EMR spectra measurements revealed a significant anisotropy with a large contribution of the nanoparticles’ surface anisotropy. The FR maximum centered near 700 nm is a characteristic feature of the investigated glasses.

A Comparative Study of -Fe2O3 and ϵ-Fe2O3 Nanoparticles Arising in Borate Glasses Doped with Fe and Gd

Formation and properties of the iron oxides γ-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 properties.

Magnetooptical Studies of Nanoparticle-Containing Borate Glasses

Faraday rotation (FR) and magnetic circular dichroism (MCD) of nanocomposite structures based on potassium-aluminum-germanium-boron glasses co-doped with Fe and rare earth (RE) or Y+Bi oxides have been studied. Formation of magnetic nanoparticles as a result of the glass heat treatment ensures them magnetic and magneto-optical properties typical of magnetically ordered substances. At the same time, glasses keep transparence in visual spectral range owing to low paramagnetic oxides concentration. FR and MCD spectra of the heat treated glasses are shown to be very close to those of γ-Fe2O3 and practically independent of the RE element nature for the light wave energies lower than 22000 cm-1. For higher energies, the MCD spectrum shape depends strongly on RE what evidences the different origin of magneto-optical effects in two spectral ranges.

Oxide glasses doped with 3d and 4f elements (Transparent Magnets): Structure, magneto-optics, magnetic resonance

Glasses of composition Al2O3-K2O-GeO-B2O3 doped with rare earths Tb, Dy, Ho, Yb, Gd were investigated. After thermal treatment, magnetic nanoparticles appeared with a structure that could not be identified unambiguously using electron microscopy and electron micro diffraction. Study of the magnetic circular dichroism revealed the structure of the forming nanoparticles to be similar to that of the spinel γ-Fe2O3. The high values of the remnant Faraday effect allow us to consider the investigated glasses as transparent permanent magnets.

Structural and magnetic ordering in nanoparticles of complex 3d- and 4f-element oxides in germanate glass

Germanate glasses doped simultaneously with Fe and rare earth elements Gd, Tb, Dy, and Ho in concentrations of several percent have been investigated. It is shown that the phase state of paramagnetic elements changes from isolated ions and small clusters in the initial glass to crystalline magnetic nanoparticles in the samples subjected to heat treatments. The field dependences of the magnetization of such samples are characterized by magnetic saturation in fields of about 1 kOe and large Faraday rotation in the near-IR region (up to 10 deg/cm in the range from 700 to 800 nm).

Faraday effect and aggregation of paramagnetic ions in borate glasses

The magneto-optical Faraday effect and electron spin resonance (ESR) in a potassium-aluminum borate glass containing small amounts of impurities of Fe and Mn oxides have been investigated. The Faraday effect measurements and ESR data made it possible to reveal the formation of clusters of paramagnetic ions interacting via oxygen even in the stage of glass synthesis. Heat treatment leads to cluster coarsening and formation of nanoparticles.