No abstract

Nominally pure nanocrystalline KTaO 3 was thoroughly investigated by micro-Raman and magnetic resonance spectroscopic techniques. In all samples the defect driven ferroelectricity and magnetism are registered. Both ordering states are suggested to appear due to the iron atoms and oxygen vacancies. The concentration of defects was estimated to be 0.04 and 0.06-0.1 mole %, respectively. Note that undoped single crystals of KTaO 3 are nonmagnetic and have never exhibited ferromagnetic properties. The results enable us to refer a nanosized KTa(Fe)O 3 to the class of multiferroics and assume that it could perform the magnetoelectric effect at T<29 K. It was also established that the critical concentration of impurity defects necessary to provoke the appearance of the new phase states in the material strongly correlates with the size of the particle; as the size of the particle decreases, the critical concentration decreases as well.

No abstract

The influence of the substitutional atoms Cr, Mn, Ni, Cu, Mo in iron-based alloys on the stability of the crystalline fcc structure and the change of the electron state density at the Fermi surface are studied by means of conduction electron spin resonance (CESR). The temperature dependence of the CESR g-factor and of its integral intensity is measured and analysed in relation to theoretical predictions. It is shown that Cr, Mn and Mo decrease the state density at the Fermi surface in the fcc iron, whereas Ni and Cu increase it. The study singles out the contributions of three electron subsystems (conduction s electrons, localized isolated d electrons and those included in superparamagnetic clusters) to g(T) and traces the important role of substitutional alloying elements in the formation of clusters in fcc solid solution.

Newly synthesized undoped and iron-doped nanoscale powders of KNbO3 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 (&lt;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.