Dielectric Properties and Electron Paramagnetic Resonance of Nanocrystalline Potassium Tantalate

Specific features of the EPR spectra of KTaO3: Mn nanopowders

“…In KTaO 3 single crystals, ferromagnetic properties have also never been observed. However, recent investiga tions of nanocrystalline powders of nominally pure potassium tantalate have revealed two distinctive properties: the occurrence of a ferroelectric phase transition at a temperature T c = 29 K and ferromag netism [2,3]. The manifestation of new phase states in a material suggests that this material can be assigned to the class of multiferroics, i.e., to the class of substances that are characterized by two (or more) order parame ters simultaneously (in our case, these are spontane ous polarization and spontaneous magnetization).…”

Defect driven ferroelectricity and magnetism in nanocrystalline KTaO3

“…As it was defined in our previous paper [22], the magnetic resonance spectrum of nanocrystalline potassium tantalate consists of two types of signals, a broad ferromagnetic resonance (FMR) signal, and an electron paramagnetic resonance (EPR) signal. Below the nature of both signals are thoroughly investigated.…”

“…where q r ω is a dispersion curve of the lowest TO 1 frequency of KTaO 3 , which can be written as [22]. D is a phonon parameter that was regarded as an isotropic and temperature independent in our fitting procedure.…”

“…Using the random field theory one could estimate the ferroelectric phase transition temperature in the incipient ferroelectrics with known defect concentration , namely [43]: experiments [22]. Estimations are made for two defect centers (see Table 1), which are considered below as possible origin of the polar nanoregions.…”

“…21 Ceramic samples were made from this powder, and some interesting effects were observed. 22 Firstly, a wide peak at 20-30 K was observed in the temperature dependence of dielectric constant. Maximum value of dielectric constant ε m was about 400 at 26 K. Since the dielectric peak did not shift to higher temperature as the measuring frequency was increased from 25 Hz to 1 MHz, it was suggested that the transition to the polar ordered phase takes place.…”