Il-Kyoung Jeong

Direct observation of the formation of polar nanoregions in Pb(Mg1/3Nb2/3)O3 using neutron pair distribution function analysis

Using neutron pair distribution function analysis over the temperature range from 1000 to 15 K, we demonstrate the existence of local polarization and the formation of medium-range, polar nanoregions (PNRs) with local rhombohedral order in a prototypical relaxor ferroelectric Pb(Mg(1/3)Nb(2/3))O3. We estimate the volume fraction of the PNRs as a function of temperature and show that this fraction steadily increases from 0% to a maximum of approximately 30% as the temperature decreases from 650 to 15 K. Below T approximately 200 K the volume fraction of the PNRs becomes significant, and PNRs freeze into the spin-glass-like state.

High-Performance Lead-Free Piezoceramics with High Curie Temperatures.

A bismuth ferrite and barium titanate solid solution compound can achieve good piezoelectric properties with a high Curie temperature when fabricated with low-temperature sintering followed by a water-quenching process, with no complicated grain alignment processes performed. By adding the super-tetragonal bismuth gallium oxide to the compound, the piezoelectric properties are as good as those of lead zirconate titanate ceramics.

High-temperature structural evolution of hexagonal multiferroic YMnO3 and YbMnO3

Neutron powder diffraction studies on the structural evolution of hexagonal multiferroic YMnO3 and YbMnO3 from 1000 K to 1400 K, and from 1000 K to 1350 K, respectively, are presented. The temperature evolution of diffraction patterns suggests that YMnO3 undergoes a phase transition to a non-polar structure above 1200 K, while YbMnO3 remains ferroelectric up to 1350 K. Detailed structural parameters were obtained as a function of temperature from Rietveld refinements. Based on this result, the distinct differences in temperature behaviour between YMnO3 and YbMnO3, and the origin of the ferroelectricity in these hexagonal multiferroics are discussed.

Giant magnetoelectric effect in multiferroic HoMnO3 with a high ferroelectric transition temperature

We present an example of giant magnetoelectric effect in a conventional multiferroic

A study of the correlation between hydrogen content and magnetism in ZnCoO

{\text{HoMnO}}_{3}

Structural study on the phase separation in Sm1−xCaxMnO3 (0.8≤x≤0.92)

, where polarization is very large

Soft modes and local structural transitions in Pb-free Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3 (x = 0.5): Pressure- and temperature-dependent Raman studies

(\ensuremath{\sim}56\text{ }\text{mC}/{\text{m}}^{2})

Structural evolution of bismuth sodium titanate induced by A-site non-stoichiometry: Neutron powder diffraction studies

and the ferroelectric transition temperature is higher than the magnetic ordering temperature by an order. We attribute the characteristic of the giant magnetoelectric effect to the ferroelectricity induced entirely by the off-center displacement of rare-earth ions with large magnetic moments. This finding suggests an avenue to design multiferroics with large polarization and higher ferroelectric transition temperature as well as large magnetoelectric effects.

Determination of the local symmetry and the multiferroic-ferromagnetic crossover in Ni3−xCoxV2O8 by using Raman scattering spectroscopy

Through the hydrogen treatment of Co-doped ZnO (ZnCoO), the Co-H-Co complex manifests the magnetization mediated by H. The increase in hydrogen content causes an increase in the number of Co-H-Co units, which can be controlled by the hydrogen treatment conditions. The 15 mol. % ZnCoO showed a proportional tendency between the hydrogen content and remnant magnetization under different conditions of rf power for the plasma treatment. The 20 mol. % sample showed deviation from the proportional tendency by the existing CoO phase before hydrogen injection and the formation of the Co metal phase after hydrogen injection. If one ensures the enhanced solubility limit of Co in ZnO and uses the correlation between the hydrogen content and magnetization below the solubility limit, this magnetic tool may be a good method for the measurement of the hydrogen content.

Local structural disorder in Zn0.9Co0.1O nanocrystals studied using neutron total scattering analysis

We have investigated the details of phase separation in the electron-doped manganites Sm1−xCaxMnO3 (0.8≤x≤0.92) by using temperature dependent x-ray diffraction. The lattice of the low-temperature orthorhombic phase is distorted to various extents according to the strength of the coexisting monoclinic phase. Meanwhile, the room-temperature lattice becomes more distorted due to the increasing Jahn–Teller active Mn3+ ions by Sm3+ doping. On the other hand, the substitution of Ca2+ with Sm3+ introduces the Mn3+–Mn4+ pairs, which favor the double exchange ferromagnetism. As a result of the competition between the lattice distortion and electron doping level, the modified phase diagram have been presented, including the high-temperature Griffiths phase and the ground state with competing multiphases.