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Anisotropic Spin Excitations in Spin-Peierls CuGeO3
Kazuhiko Ikeuchi,Ryoichi Kajimoto,Fumio Mizuno,Masaki Fujita,Yasuhiro Inamura,Mitsutaka Nakamura,Kenji Nakajima,Kazuya Aizawa,Masatoshi Arai 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We report on the investigation of spin excitations in CuGeO3 at a low temperature by usinginelastic neutron scattering on a pulsed source with a time-of-flight analysis. By observing thedispersion relation of spin excitations not only along the chain direction but also along the interchain direction, we studied spin correlations in the S = 1/2 Heisenberg chains, as well as between thechains, in detail. The results show a clear anisotropy of the magnetic excitations at a temperaturebelow the spin-Peierls transition temperature.
High-energy Magnetic Excitations in Underdoped La1.90Sr0.10CuO4
Kentaro Sato,Masato Matsuura,Masaki Fujita,Ryoichi Kajimoto,Sungdae Ji,Kazuhiko Ikeuchi,Mitsutaka Nakamura,Yasuhiro Inamura,Masatoshi Arai,Masanori Enoki,Kazuyoshi Yamada 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We measured the magnetic excitations in underdoped (UD) La1.90Sr0.10CuO4 by using inelasticneutron scattering over a wide energy range. We succeeded in observing the high-energy excitationsup to '160 meV. Hour-glass-like magnetic excitation, which is commonly seen in the superconductingphase of cuprate oxides, was confirmed. The Ecross (the energy where the dispersion is closestto the ( 12 , 12 ) reciprocal position) of 40 meV follows a linear relation between Ecross and the dopedhole concentration in the UD region. From the dispersion of high-energy excitations above Ecross,we successfully found an effective nearest neighbor interaction (Jeff ) of 102 ± 2 meV. This Jeff issmaller than the nearest neighbor interaction J(=132 meV) in the parent compound La2CuO4,indicating a reduction of Jeff by hole-doping.
The Effect of Pressure on the Poling Condition in Lead-based Relaxor Ferroelectric Solid Solutions
Naohiko Yasuda,Naoki Miyazono,Hidehiro Ohwa,Yoshihito Tachi,Yohachi Yamashita,Kazuhiko Fujita,Makoto Iwata,Yoshihiro Ishibashi 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
Topographic images for the domain structures of etched surfaces of PMNT ceramics were observed: ① Flattened fine domain structures with domains of about 50 nm or less in size along the poling direction due to the 180 domain reversal were seen in rhombohedral (74/26), (72/28), and (69/31) ceramics. ② Stereographical fine domain structures with projected domains of about 50 nm or less in size along some directions due to non-180˚ domain reversal, as well as 180˚ domain reversal were seen in the (67/33) ceramic near a MPB composition. Pressure-induced suppression of the electromechanical response occurred at the depoling pressure p_d = 590 MPa for PMNT (67/33) and at p_d = 400 MPa for PMNT (69/31). The poling for the PMNT (72/28) ceramic under a pressure of 600 MPa above pd was done under decreasing pressure at 10 kV/cm at room temperature. The resonance frequency fr and the antiresonance frequency fa decreased to f_r = 121.74 kHz and f_a = 124.03 kHz, the electromechanical coupling coefficient k31 decreased to 20.5%, and the maximum phase angle θ_m decreased to 12˚ compared to f_r = 131.32 kHz and f_a = 135.37 kHz, k31 = 26.8% and θ_m = 52˚ for normal poling. The topographic images of the etched surface of PMNT (72/28) poled under pressure was characterized with stereographical fine domain structures with projected domains of about 100 nm or less in size along some directions due to non-180 domain switching. A poling process using depoling pressure, as well as the well-known normal poling using depoling temperature, is applicable for ferroelectric materials.
Naohiko Yasuda,Aritoshi Nakada,Hidehiro Ohwa,Ikuo Suzuki,Kazuhiko Fujita,Makoto Iwata,Masaki Maeda,Ryouko Ozao,Yoshihiro Ishibashi 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
The relation between polarization P and electric eld E in the solid solutions (1 .. x)Pb(Sc1=2Ta1=2)O3-xPbZrO3(PST-PZ) was investigated with the successive antiferroelectric (AFE) - ferroelectric(FE) - paraelectric(PE) phase transition with heating in the range of PZ compositions x > 0:8. It was found that P{E hysteresis loops change from the double P{E loop to the single one, re ecting the phase transition from AFE to FE. For the switching behavior in the AFE phase, it was found that the electric eld dependence of the reciprocal switching time and the peak switching current which characterize the switching transient consists of two parts ; one is the linear part at the high-eld region and the other is the curved part at the low-eld region.