Abstract
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 (<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.
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