Possibility Of Ferroelectricity Research Articles

Magnetic and dielectric properties of Ba-lacunar La0.5Eu0.2Ba0.3MnO3 manganites synthesized using sol-gel method under different sintering temperatures

Structural, magnetic and dielectric properties of La0.5Eu0.2Ba0.3−x□xMnO3 (x = 0.00, 0.05 and 0.15) perovskites are investigated. Nano-polycrystalline samples prepared using sol-gel wet chemical method were subjected to annealing in two different temperatures and investigated by powder X-ray diffraction (XRD), magnetometry, and ac impedance spectroscopy. XRD characterizations indicated that all samples exhibited a single rhombohedral phase. The temperature-dependent magnetizations indicate the ferromagnetic transition. The resistivity decreased and the magnetic ordering temperature increased as Ba-deficiency increased. The dielectric constant dependent on frequency shows normal behavior. The samples with a lower sintering temperature show the highest resistivity and dielectric constant. Dielectric anomaly dependent on temperature was observed close to the magnetic ordering temperature, indicating the possibility of ferroelectricity and further magnetoelectric coupling. The dielectric behaviors have been interpreted based on space charge polarization according to Maxwell-Wagner’s two-layer model and hopping of charge between Mn3+ and Mn4+ ions.

B-site ordering, magnetic and dielectric properties of hydrothermally synthesized Lu2NiMnO6

The double peroskite Lu2NiMnO6 was synthesized by a facile hydrothermal method. X-ray power diffraction (XRD) analysis shows it adopts monoclinic structure with space group P21/n, indicating an ordered arrangement at B sites. Valence states analysis done by XPS shows Ni2+/Mn4+ configuration. Raman spectrum reveals an ordered structure in the sample, in agreement with the XRD results. The degree of ordering was greatly enhanced after the sample was annealed at 873 K. Magnetism of the as-grown and annealed samples was analyzed using DC and AC magnetization, as well as Magnetization-Hysteresis. Dielectric anomaly independent on frequency was observed close to the magnetic ordering temperature, indicating the possibility of ferroelectricity and further magnetoelectric coupling.

Magnetoelectric effect and low-temperature phase transitions in YMn2O5

Abstract A possibility of ferroelectricity has been proposed in some low temperature phases of the oxides of the series RMn2O5 (R = a rare earth from Nd to Lu, Y or Bi). YMn2O5 is unusual in this series, because Y3+ is non-magnetic. We made dielectric, magnetic and magnetoelectric measurements on single crystals of this oxide to detect two electric transitions at 39 K and 19 K. These transitions are accompanied with anomalies in the dielectric constant and the magnetic and the magnetoelectric susceptibilities. Particularly, the sign of the magnetoelectric susceptibility is switched below 19 K, depending on the sense of the electric field applied during cooling the sample down to 4.2 K. This fact indicates that YMn2O5 possesses spontaneous polarization at least below 19 K.

Possibility of ferroelectricity in Yttrium iron garnet single crystal

Abstract We observed the first order magnetoelectric effect in a YIG single crystal in the temperature range below 125 K. The magnetoelectric signal was strongly influenced by the electric field applied along the [110] direction during cooling the sample down to 77 K. It reversed the sign when the electric field was applied in the opposite direction during cooling. Its magnitude composed of two parts; the one which was linear in the cooling field and the residual part. From the experimental results we conclude that YIG has a phase transition at 125 K below which it is a polar crystal.

Electrical studies in some alkali titanates

D.C. electrical conductivity of Na 2Ti 3O 7, NaKTi 3O 7, K 2Ti 4O 9 and KRbTi 4O 9 pelletized samples has been studied in the temperature range between 400 K and 800 K. Dependence of loss tangent (tan δ) on temperature and frequency has been studied in detail for Na 2Ti 3O 7 and NaKTi 3O 7. The results indicate possibility of ferroelectricity at higher temperatures.

On the possibility of ferroelectricity in liquid crystalline polymers

The model of ferroelectric liquid crystalline polymers is suggested. The model describes properties of the aligned polymer media doped by spontaneously polarized solid grains. The phase transition in small grains is considered and the behaviour of the bulk system in the external field is investigated. Results are compared with the available experimental data. The process of the long-lived bulk polarization creation is described.