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Golovina I.,Institute of Semiconductor Physics of Ukraine | Shanina B.,Institute of Semiconductor Physics of Ukraine | Kolesnik S.,Institute of Semiconductor Physics of Ukraine | Geifman I.,Quality Engineering Education Inc. | Andriiko A.,Kharkiv Polytechnic Institute
Physica Status Solidi (B) Basic Research | Year: 2012

Magnetic defects in non-doped and iron-doped nanopowders of KTaO 3 were studied by resonance and static magnetic measurements. The resonance spectra and hysteresis loops of KTaO 3:Fe nanocrystalline powders were observed and investigated for the first time. Unlike bulk crystals, both non-doped and doped nanopowders exhibit two types of resonance lines, paramagnetic ones from the isolated Fe 3+ ions and a ferromagnetic signal from ions involved in clusters. Theoretical description and full identification of the electron paramagnetic resonance (EPR) spectra were made. It was established that low doping (up to 0.4mol%) increases the number of paramagnetic Fe 3+ centers with axial and rhombic symmetries, and has no effect on the centers with cubic symmetry and magnetic clusters. Analysis of the temperature dependence of the spectra showed that the cluster's resonance line follows the Bloch law "T 3/2", which indicates a ferromagnetic nature of the cluster. A partial collapse of the ferromagnetic subsystem in the temperature range of 100-400K was also found. Magnetization and other characteristics of ferromagnetic and paramagnetic subsystems were determined. An average cluster size was estimated to be equal to a length of 6.2nm and the fractional volume of the ferromagnetic cluster system was found. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Golovina I.S.,Ukrainian Academy of Sciences | Shanina B.D.,Ukrainian Academy of Sciences | Geifman I.N.,Quality Engineering Education Inc. | Andriiko A.A.,Kharkiv Polytechnic Institute | Chernenko L.V.,Kharkiv Polytechnic Institute
Physics of the Solid State | Year: 2012

The electron paramagnetic resonance spectra of KTaO 3: Mn nanocrystalline powders in the temperature range from 77 to 620 K have been measured and studied for the first time. The change observed in the spectra has been investigated as a function of the doping level. The doping regions in which Mn 2+ ions are individual paramagnetic impurities have been established, as well as the regions where the dipole-dipole and exchange interactions of these ions begin to occur. The spin-Hamiltonian constants for the spectrum of non-interacting individual Mn 2+ ions have been determined as follows: g = 2. 0022, D = 0. 0170 cm -1, and A = 85 × 10 -4 cm -1. A significant decrease in the axial constant D in the KTaO 3: Mn nanopowder, as compared to the single crystal, has been explained by the remoteness of the charge compensator from the paramagnetic ion and by the influence of the surface of the nanoparticle. It has been assumed that the Mn 2+ ions are located near the surface and do not penetrate deep into the crystallites. © 2012 Pleiades Publishing, Ltd.

Golovina I.S.,Ukrainian Academy of Sciences | Bryksa V.P.,Ukrainian Academy of Sciences | Strelchuk V.V.,Ukrainian Academy of Sciences | Geifman I.N.,Quality Engineering Education Inc.
Functional Materials | Year: 2013

Raman spectra of KTa0.5Nb0.503 nanopowder solid solution were obtained at the temperatures from -190°C to 600°C and investigated for the first time. The compound was synthesized by a new technology. Temperature dependences of the intensity, width and frequency of the B1(T02), A1(TO1), B1(TO3), A1(T03) and B2(TO3) modes are thoroughly analyzed. A significant expanding of the temperature ranges of all phase transitions, correlated with a spread of particle sizes is registered. It was found that an average temperature of each of the phase transitions is shifted in different way, in particular: a low-temperature transition at 30 degrees higher, the middle transition at 10 degrees higher, and the ferroelectric phase transition occurs at 20 degrees lower than the temperature of the corresponding transitions in single-crystal KTa0.5Nb0.5O3. © 2013-STC "Institute for Single Crystal".

Golovina I.S.,Institute of Semiconductor Physics of Ukraine | Kolesnik S.P.,Institute of Semiconductor Physics of Ukraine | Geifman I.N.,Quality Engineering Education Inc. | Belous A.G.,Ukrainian Academy of Sciences
Review of Scientific Instruments | Year: 2010

We have developed and tested two types of novel dielectric resonators for simultaneous recording of electron paramagnetic resonance (EPR) spectra from two to four samples. The resonator of the first type contains two holes, and the other resonator contains four holes for introduction of the samples. Also, the resonator structure includes a pair of gradient coils. Dielectric resonators made of materials with high dielectric constant with low losses can be inserted into the standard EPR cavity or waveguide in the maximum microwave magnetic field. Gradient coils are located outside the cavity (or waveguide) so that their axes are parallel to the static magnetic field. Computer simulations were made to obtain microwave characteristics of the resonators such as resonant frequency, sizes, and distribution of the fields. Spacing of the point samples and optimum value of the magnetic-field gradient have been chosen correctly. The designed resonators can be applied in express analysis using EPR technique, for instance. © 2010 American Institute of Physics.

Golovina I.S.,Institute of Semiconductor Physics of Ukraine | Shanina B.D.,Institute of Semiconductor Physics of Ukraine | Kolesnik S.P.,Institute of Semiconductor Physics of Ukraine | Geifman I.N.,Quality Engineering Education Inc. | Andriiko A.A.,Kharkiv Polytechnic Institute
Journal of Applied Physics | Year: 2013

Newly synthesized undoped and iron-doped nanoscale powders of KNbO 3 are investigated using magnetic resonance and static magnetization methods in order to determine how the crystal size and doping affect the structure of magnetic defects and material properties. Although the bulk crystals of KNbO3 are nonmagnetic, the undoped KNbO3 powder with average particle size of 80 nm exhibits magnetic properties. The ferromagnetic resonance signal and the magnetization curve registered on the powder are thoroughly analyzed. It is concluded that the appearance of the defect driven ferromagnetism in the undoped powder is due to the nano-size of the particles. This effect disappears in the iron-doped KNbO3 powder with particle sizes above 300 nm. In case of low doping (<1 mol. % Fe), a new electron paramagnetic resonance signal with geff = 4.21 is found out in the KNbO3:Fe powder. Such a signal has not been observed in the bulk crystals of KNbO3:Fe. We suppose that this signal corresponds to individual paramagnetic Fe3+ ions having rhombic symmetry. © 2013 AIP Publishing LLC.

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