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Lattice Modulation in YMn2O5 and TbMn2O5 Studied by Using Synchrotron Radiation X-rays
Yukio Noda,H Kimura,H Sawa,K Kohn,N Ikeda,S Kobayashi,Y Ishikawa,Y Kamada,Y Wakabayashi 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
RMn2O5 (R = Y and rare earth) shows successive magnetic and ferroelectric phase transitions at about 45 K, 40 K, 39 K, 20 K and 10 K and is called a multiferroic compound. We have investigated the lattice modulation vectors (qL) of YMn2O5 and TbMn2O5 by using single crystal Synchrotron Radiation X-ray diraction and compared them with the magnetic propagation vectors (qM) studied by neutron diraction. The relation of the propagation vectors between magnetic materials and dielectrics is found to be qL = 2qM. A preliminary structure analysis of the atomic displacement pattern in the commensurate ferroelectric phase of TbMn2O5 is discussed.fb
Satoru Kobayashi,Hiroyuki Kimura,Isao Kagomiya,Kay Kohn,Toshihiro Osawa,Yukio Noda 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
A ferroelectric phase transition of RMn2O5 (R = rare earth,Bi,Y) has been systematically reinvestigated by dielectric measurements. In addition to a sharp peak of the dielectric constant along the b axis at the temperature of ferroelectric phase transition, TC1, we observed a small kink at TS slightly below TC1 for R = Er, Y, Tb, Tm. Correspondingly, two-step successive magnetic phase transitions were found for R = Er, Y, Tm in a narrow temperature range of 1 K around TC1 by neutron diraction measurements. The comparison between temperatures of dielectric anomalies and magnetic phase transitions indicates that the paraelectric-ferroelectric phase transition at TC1 is induced by a commensurate magnetic ordering along the c axis in RMn2O5.
Ordering Process in Sodium Nitrite Observed by Using Neutron Diffractometry
Hiroyuki Mashiyama,Tatsuki Miyoshi,Takanao Asahi,Hironobu Kasano,Yukio Noda,Hiroyuki Kimura 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
From neutron diffraction data, the nuclear density of sodium nitrite is guessed directly by a maximum entropy method, and is compared with the results of usual least-squares calculations. The obtained nuclear density displays that the disordered NO_2 molecule becomes partially ordered in the ferroelectric phase just below the transition temperature. However, the density distribution cannot be explained by a two-Gaussian function, which suggests that the ordering is not a classical stochastic process but a quantum tunneling in a double minima local potential.
Properties of spin-12triangular-lattice antiferromagnetsCuY2Ge2O8andCuLa2Ge2O8
Cho, Hwanbeom,Kratochví,lová,, Marie,Sim, Hasung,Choi, Ki-Young,Kim, Choong Hyun,Paulsen, Carley,Avdeev, Maxim,Peets, Darren C.,Jo, Younghun,Lee, Sanghyun,Noda, Yukio,Lawler, Michael J.,Pa American Physical Society 2017 Physical review. B Vol.95 No.14
<P>We found new two-dimensional (2D) quantum (S = 1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE = Y and La). According to our analysis of high-resolution x-ray and neutron diffraction experiments, the Cu network of CuRE2Ge2O8 (RE = Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of E-g congruent to 2 eV. Taken together, our observations make CuRE2Ge2O8 (RE = Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering.</P>