Eun Ok Chi

Bulk characterization methods for non-centrosymmetric materials: second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity

Characterization methods for bulk non-centrosymmetric compounds are described. These methods include second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity. In this tutorial review with each phenomenon, details are given of the measurement techniques along with a brief history and background. Finally, data interpretation is discussed.

Colossal magnetoresistance in perovskite manganite induced by localized moment of rare earth ion

Abstract The magnetic and transport properties of a single crystal of Pr 0.7 Ca 0.3 MnO 3 annealed by various magnetic fields were investigated by dc and ac magnetization measurements. The ordered Pr moment is almost absent in zero-field magnetization but is clearly observed when the sample was measured after annealing with a magnetic field. The Pr moment is enhanced when the annealing field is increased. Remarkably, the ordered Pr spins appear to induce colossal magnetoresistance (∼10 10 %) as well as a metal–insulator (M–I) transition in Pr 0.7 Ca 0.3 MnO 3 . This unique behavior is discussed in terms of the reorientation of Pr spins that are strongly coupled with the neighboring Mn spins.

Chemical Pressure Effects of Cation Size Variation in Layered Manganites.

We have investigated the electric and magnetic properties of the layered manganite (La 1- y R y ) 2-2 x Sr 1+2 x Mn 2 O 7 (R=Pr, Nd, Sm, Eu, Gd; x =0.3) with the fixed doping concentration. The ave...

Fabrication of TiO2 nanospheres by template replication in porous carbon networks

A silica-colloidal template approach was used to prepare monodisperse nanospheres of TiO 2 . Close-packed arrays of silica spheres were infiltrated with a sucrose precursor used as a source of carbon. The infiltrated sucrose was carbonized by calcination at 800 °C in flowing argon. After removal of the silica spheres by washing with HF, a porous carbon replica remained. The resulting pores in the replica were then filled with a chloroform solution of titanium alkoxide. Nanospheres of TiO 2 approximately 200 nm in diameter were obtained after calcination of the organic component at 600 °C in an argon atmosphere and subsequent sintering in air at 700 °C.

Macroscopic phase separation in layered manganite induced by a surface effect

Abstract We report on the origin of the perovskite phase intergrown in the layered manganite, Sr 1.6 La 1.4 Mn 2 O 7 . X-ray powder diffraction, magnetization, and transport measurements on the Sr 1.6 La 1.4 Mn 2 O 7 materials prepared under various conditions show that the perovskite phase is grown predominantly on the surface region in contact with either air or the substrate. With intermediate grinding and sintering the perovskite impurity increases rather than transforms to Sr 1.6 La 1.4 Mn 2 O 7 . The results provide important information for the understanding of the layered manganite system in which the compositional fluctuation occurs naturally due to the intergrown perovskite phase.

Magnetic Glassiness below Curie Temperature in La0.8Ca0.2MnO3

The magnetic and structural behaviors of a single crystal of La 0.8 Ca 0.2 MnO 3 were investigated in terms of magnetic and neutron diffraction measurements. The frequency-dependent ac magnetic susceptibility reveals that cluster-glassy phase evolves below the Curie temperature ( T C ) in this system, suggesting the existence of short-range correlation below T C embedded in the ferromagnetic (FM) background. A correlation of the magnetic properties in La 0.8 Ca 0.2 MnO 3 with the buckling of MnO 6 octahedra is discussed based on its temperature-dependent neutron and magnetization data.

Effect of Subsidiary Phase on the Magnetic and Transport Properties of Sr1.6La1.4Mn2O7

Temperature and field dependent magnetic and transport measurements on a polycrystalline sample of Sr 1.6 La 1.4 Mn 2 O 7 reveal distinct magnetic peaks above the ferromagnetic ordering temperature T C 90 K. The magnetic moment of the subsidiary phases identified as perovskitic impurities by a relation between the volume fraction and the corresponding magnetic moment does not couple with that of Sr 1.6 La 1.4 Mn 2 O 7 in the high temperature range. This is evidenced by the presence of two slopes, dM/dH, in the M(H) curves and two different field dependences, H and H 2 , in the Q(H) curves. On the other hand, a simple slope, dM/dH, in the low temperature regime hints at an exchange coupling between the magnetic moments of the two phases.