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Hiroyuki Kimura,K Kohn,K Kakurai,K Kaneko,N Metoki,S Wakimoto,Y Kamada,Y Noda 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
A microscopic magnetic phase diagram as functions of temperature and magnetic .eld was mapped for multiferroic compounds of RMn2O5 (R = Er, Ho) by using neutron diraction mea- surements under high magnetic .eld. The unambiguous relation between the ferroelectric phase transition and the magnetic phase transition from a two-dimensional incommensurate to a com- mensurate phase, where both the transitions are concomitantly induced by the magnetic .eld, indicates that the electric polarization is magnetically induced and the commensurate spin state is important for stabilizing the ferroelectricity in the multiferroic RMn2O5 system. The origin of the .eld-induced magnetic phase transition is discussed based on the magnetic structure. j_si
稀薄溶液에서의 Polymer의 熱分解. Hydroquinone의 영향
Won, Yeong-Moo,Fukutomi, Takashi,Kakurai, Toshio,Noguchi, Tatsuya 대한화학회 1972 대한화학회지 Vol.16 No.2
The thermal degradation of poly (${\alpha}$-methyl styrene) in several mixed solvents (toluene-n-butylalcohol, toluene-sec-butylalcohol, toluene-kerosene, toluene-methyl ethyl ketone) without hydroquinone, and in with the addition of the hydroquinone, was studied at temps. of $165^{\circ}{\sim}205^{\circ}C$. The velocity constant of degradation (k), and the activation energy (E) were calculated for each solvent. As results, k decreased with the increase of the volume-fraction of poor solvent in both systems, whereas E either showed no perceptible change or it increased with the volume-fraction of poor solvents. these results were discussed.
稀薄溶液에서의 polymer의 機械的切斷. 切斷에 미치는 온도의 영향
Won, Yeong-Moo,Takashi Fukutomi,Toshio Kakurai,Tatsuya Noguchi 대한화학회 1971 대한화학회지 Vol.15 No.3
The mechanical degradation of poly (${\alpha}$-methyl styrene) in several mixed solvents (toluene-n-butyl alcohol, toluene-sec-butyl alcohol, toluene-kerosene, toluene-methyl ethyl ketone), from $1^{\circ}C to $45^{\circ}C$, was studied using the capillary flow method. The velocity constant of scission reaction (k) and the limited degree of polymerization (g) were compared at the same value of [${\eta}$] at each temperatures. As results, mechanical degradation of polymer in dilute mixed solutions is affected by composition of solvents around the polymer chains.
Nirmala, R,Jang, Kwang-Hyun,Sim, Hasung,Cho, Hwanbeom,Lee, Junghwan,Yang, Nam-Geun,Lee, Seongsu,Ibberson, R M,Kakurai, K,Matsuda, M,Cheong, S-W,Gapontsev, V V,Streltsov, S V,Park, Je-Geun Institute of Physics 2017 Journal of Physics, Condensed Matter Vol.29 No.13
<P>CuAl<SUB>2</SUB>O<SUB>4</SUB> is a normal spinel oxide having quantum spin, <I>S</I> = 1/2 for Cu<SUP>2+</SUP>. It is a rather unique feature that the Cu<SUP>2+</SUP> ions of CuAl<SUB>2</SUB>O<SUB>4</SUB> sit at a tetrahedral position, not like the usual octahedral position for many oxides. At low temperatures, it exhibits all the thermodynamic evidence of a quantum spin glass. For example, the polycrystalline CuAl<SUB>2</SUB>O<SUB>4</SUB> shows a cusp centered at ~2 K in the low-field dc magnetization data and a clear frequency dependence in the ac magnetic susceptibility while it displays logarithmic relaxation behavior in a time dependence of the magnetization. At the same time, there is a peak at ~2.3 K in the heat capacity, which shifts towards a higher temperature with magnetic fields. On the other hand, there is no evidence of new superlattice peaks in the high-resolution neutron powder diffraction data when cooled from 40 to 0.4 K. This implies that there is no long-ranged magnetic order down to 0.4 K, thus confirming a spin glass-like ground state for CuAl<SUB>2</SUB>O<SUB>4</SUB>. Interestingly, there is no sign of structural distortion either although Cu<SUP>2+</SUP> is a Jahn–Teller active ion. Thus, we claim that an orbital liquid state is the most likely ground state in CuAl<SUB>2</SUB>O<SUB>4</SUB>. Of further interest, it also exhibits a large frustration parameter, <I>f</I> = |<I>θ</I> <SUB>CW</SUB>/<I>T</I> <SUB>m</SUB>| ~ 67, one of the largest values reported for spinel oxides. Our observations suggest that CuAl<SUB>2</SUB>O<SUB>4</SUB> should be a rare example of a frustrated quantum spin glass with a good candidate for an orbital liquid state.</P>
Frustrated minority spins in GeNi<sub>2</sub>O<sub>4</sub>
Matsuda, M.,Chung, J.-H.,Park, S.,Sato, T. J.,Matsuno, K.,Aruga Katori, H.,Takagi, H.,Kakurai, K.,Kamazawa, K.,Tsunoda, Y.,Kagomiya, I.,Henley, C. L.,Lee, S.-H. Editions de Physique 2008 Europhysics letters Vol.82 No.3
<P>Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi<SUB>2</SUB>O<SUB>4</SUB> at <I>T</I><SUB><I>N</I>1</SUB>=12.1 K and <I>T</I><SUB><I>N</I>2</SUB>=11.4 K, respectively (Crawford M. K. <I>et al</I>., <I>Phys. Rev. B</I>, <B>68</B> (2003) 220408(R)). Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at <I>T</I><SUB><I>N</I>1</SUB> the spins on the 〈111〉 kagome planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the 〈111〉 triangular planes that separate the kagome planes frustrated and disordered. At the lower <I>T</I><SUB><I>N</I>2</SUB>, the triangular spins also order in the 〈111〉 plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions.</P>
Crystal distortions in geometrically frustrated ACr<sub>2</sub>O<sub>4</sub> (A = Zn,Cd)
Lee, S-H,Gasparovic, G,Broholm, C,Matsuda, M,Chung, J-H,Kim, Y J,Ueda, H,Xu, G,Zschack, P,Kakurai, K,Takagi, H,Ratcliff, W,Kim, T H,Cheong, S-W IOP Pub 2007 Journal of Physics, Condensed Matter Vol.19 No.14
<P>In this paper, we discuss neutron and synchrotron x-ray diffraction data obtained from single crystals of ACr<SUB>2</SUB>O<SUB>4</SUB> (A = Zn, Cd). The Cr spinels undergo three-dimensional spin-Peierls transitions at low temperatures that involve cubic-to-tetragonal lattice distortions and magnetic long-range ordering. Our results show that the magnetic structures selected by these systems are closely related to the lattice distortions that are undertaken. </P>
Spiral spin structures and origin of the magnetoelectric coupling inYMn2O5
Kim, J.-H.,Lee, S.-H.,Park, S. I.,Kenzelmann, M.,Harris, A. B.,Schefer, J.,Chung, J.-H.,Majkrzak, C. F.,Takeda, M.,Wakimoto, S.,Park, S. Y.,Cheong, S-W.,Matsuda, M.,Kimura, H.,Noda, Y.,Kakurai, K. American Physical Society 2008 Physical review. B, Condensed matter and materials Vol.78 No.24