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Anisotropic Magnetic Properties in Åkermanite Sr2MSi2O7 (M=Co, Mn) Crystals
Mitsuru Akaki,Tomoya Tadokoro,Hideki Kuwahara,Takumi Kihara,Masashi Tokunaga 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We have investigated the magnetic and the dielectric properties of °akermanite Sr2CoSi2O7 and Sr2MnSi2O7 single crystals. Sr2CoSi2O7 shows a canted antiferromagnetism with a large magnetic anisotropy at temperatures below 7 K. By applying a magnetic field along the [110] direction, an electric polarization emerges along the c axis at temperatures below the magnetic transition temperature. In high magnetic fields, the saturation magnetization becomes enhanced only when the electric polarization appears. In contrast, the magnetization of Sr2MnSi2O7 is isotropic at all temperatures, and its magnetic-field-induced electric polarization is very small. These results suggest that the electronic configuration of the transition-metal ion is of crucial importance for the appearance of electric polarization.
Low-temperature Thermoelectric Properties of the Electron-doped Perovskites Sr1−xCaxTi1−yNbyO3
Tetsuji Okuda,Junichi Fukuyado,Kurahito Narikiyo,Mitsuru Akaki,Hideki Kuwahara 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have investigated the thermoelectric (TE) properties for single crystals of the perovskitesSr1−xCaxTi1−yNbyO3 for 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.03 at temperatures below room temperature(RT). We found that SrTi0.99Nb0.01O3 showed a large power factor at low temperatures (PF =50 µW/K2cm at 100 K 90 µW/K2cm at 50 K) and the largest dimensionless TE figure-ofmeritat temperatures below 40 K (ZT 0.07) among the reported materials. Such a large lowtemperatureTE response around a carrier concentration of 1020 cm−3 is due to a distinct phonondrag effect. We also found that the Ca2+ substitution for Sr2+ increased the ZT at 300 K forSr1−xCaxTi0.97Nb0.03O3 from 0.08 to 0.105. The enhancement of the ZT around RT originatesboth from a large reduction of a thermal conductivity due to a randomness introduced into thecrystal structure and from an unexpected enhancement of a Seebeck coefficient.
Control of Coexisting Ferroelectric Phases in RMnO3 Crystals with Fine Tuning of 4f Moment
Tomoya Tadokoro,Naoaki Kano,Haruhiko Kuroe,Tomoyuki Sekine,Hideki Kuwahara,Mitsuru Akaki 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have systematically investigated the magnetic and the dielectric properties of Eu0.595(Y1−xHox)0.405MnO3 (0 ≤ x ≤ 1) single crystals with fine tunning of 4f magnetic momentswhile keeping the average size of the rare-earth (R) site the same. In the x = 0.3 crystal,the ferroelectric polarization along the c axis (Pc) emerges at 25 K; then, Pc is suppressed, andPa appears simultaneously with decreasing temperature. On further decreasing temperature, Padisappears and Pc appears again. The observed reentrant behavior of the Pc phase indicates thatthe Pa and the Pc phases are strongly competing with each other.
Thermal, Dielectric, and Magnetic Properties in Multiferroic Cu2.85Zn0.15Mo2O9
Haruhiko Kuroe,Kento Aoki,Ryusuke Itoh,Tomohiro Hosaka,Takuya Hasegawa,Suguru Hachiuma,Mitsuru Akaki,Hideki Kuwahara,Tomoyuki Sekine,Masashi Hase,Kunihiko Oka,Toshimitsu Ito,Hiroshi Eisaki 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We study the effects of Zn substitution on single crystals of the low-dimensional multiferroicmaterial Cu3Mo2O9. We report the magnetic field-temperature phase diagram obtained from thetemperature and the magnetic field dependences of the specific heat, the dielectric constant, thedifferential magnetization, and the electric polarization-electric field curve in Cu2.85Zn0.15Mo2O9. We obtain three phases: a paraelectric and a ferroelectric phase, and a ferroelectric phase with alarge coercive electric field. The origin of the last one is discussed based on the charge redistributioneffect on a half-filled Mott insulator. In this phase, the Zn substitution induces a robust localizedferroelectric polarization that increases the coercive electric field.