Zentaro Honda

Field-Induced Magnetic Long-Range Order in the Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain System (CH3)2CHNH3CuCl3 Observed by Specific Heat Measurements.

The compound (CH 3 ) 2 CHNH 3 CuCl 3 has recently been found to be an ideal ferromagnetic-antiferromagnetic alternating Heisenberg chain with the energy gap Δ/ k =17∼18 K [H. Manaka et al. : J. Phys. Soc. Jpn. 66 (1997) 564]. When an external field H is applied to this compound, the energy gap should vanish at the critical field H c1 = Δ/ g µ B . Just above H c1 , the three-dimensional magnetic long-range order is expected, if the interchain coupling exists. Motivated by this expectation, we performed specific heat measurements over a temperature range from 0.5 to 5 K applying H up to 12 T. As a result, we found a λ-type anomaly of specific heat over 10∼12 T, which indicates a transition to the three-dimensional long range order. The temperature at which the λ-type anomaly appears increases with increasing H . The critical field obtained by extrapolating the curve of the λ peak position versus H is 9.0 T, which is close to that obtained from a magnetization measurement.

Observation of a transient magnetization plateau in a quantum antiferromagnet on the Kagomé lattice

The magnetization process of an S = ½ antiferromagnet on the Kagome lattice, [Cu3(titmb)2(OCOCH3)6]·H2O{titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6 trimethylbenzene}, has been measured at very low temperatures in both pulsed and steady fields. We have found a new dynamical behavior in the magnetization process. A plateau at one third of the saturation magnetization Ms appears in the pulsed-field experiments for intermediate sweep rates of the magnetic field and disappears in the steady-field experiments. A theoretical analysis using exact diagonalization yields J1 = − 19 ± 2 K and J2 = 6 ± 2 K, for the nearest-neighbor and second-nearest-neighbor interactions, respectively. This set of exchange parameters explains the very low saturation field and the absence of the plateau in the thermodynamic equilibrium as well as the two-peak feature in the magnetic heat capacity observed by Honda et al. (Z. Honda et al., J. Phys. Condens. Matter 14 (2002) L625). Supported by numerical results we argue that a dynamical order by disorder phenomenon could explain the transient appearance of the Ms/3 plateau in pulsed-field experiments.

New high magnetic field phase of the frustrated S = 1/2 chain compound LiCuVO4

Magnetization of the frustrated S = 1/2 chain compound LiCuVO4, focusing on high magnetic field phases, is reported. Besides a spin-flop transition and the transition from a planar spiral to a spin modulated structure observed recently, an additional transition was observed just below the saturation field. This newly observed magnetic phase is considered as a spin nematic phase, which was predicted theoretically but was not observed experimentally. The critical fields of this phase and its dM/dH curve are in good agreement with calculations performed in a microscopic model (M.E. Zhitomirsky and H. Tsunetsugu, Europhys. Lett. 92, 37001 (2010)).

Improved Power Conversion Efficiency of Organic Photovoltaic Cell Fabricated by Electrospray Deposition Method by Mixing Different Solvents

A smooth surface of the poly(3-hexylthiophene) (P3HT)-doped-(6,6)-phenyl-C61-butyric acid methyl ester (PCBM) thin film was achieved by mixing different solvents for the electrospray deposition method. As a result, the high power-conversion efficiency (PCE) of the bulk-heterojunction organic photovoltaic cell (OPV) was comparable to that obtained in the case of the spin-coating method. By optimizing the additional solvent in o-dichlorobenzene, the P3HT/PCBM active layer with the root-means-square roughness of 2.23 nm and the PCE of 2.2% was fabricated employing acetonitrile as the additional solvent.

Field-induced long-range ordering in an S = 1 quasi-one-dimensional Heisenberg antiferromagnet

We have measured the heat capacity and magnetization of the spin one one-dimensional Heisenberg antiferromagnet NDMAP and constructed a magnetic field versus temperature phase diagram. We found a field induced long-range magnetic ordering. We have been successful in explaining the phase diagram theoretically.

Field-Induced Three- and Two-Dimensional Freezing in a Quantum Spin Liquid

Field-induced commensurate transverse magnetic ordering is observed in the Haldane-gap compound Ni(C(5)D(14)N(2))2N(3)(PF(6)) by means of neutron diffraction. Depending on the direction of applied field, the high-field phase is shown to be either a three-dimensional ordered Néel state or a short-range ordered state with dominant two-dimensional spin correlations. The structure of the high-field phase is determined, and properties of the observed quantum phase transition are discussed.

Massive triplet excitations in a magnetized anisotropic Haldane spin chain

Inelastic neutron scattering experiments on the Haldane-gap quantum antiferromagnet Ni(C{sub 5}D{sub 14}N{sub 2}){sub 2}N{sub 3}(PF{sub 6}) are performed at mK temperatures in magnetic fields of almost twice the critical field H{sub c} applied perpendicular to the spin chains. Above H{sub c} a reopening of the spin gap is clearly observed. In the high-field Neel-ordered state the spectrum is dominated by three distinct excitation branches. A theoretical model consistently describing the experimental data is proposed.

Haldane-gap excitations in the low- H c one-dimensional quantum antiferromagnet Ni ( C 5 D 14 N 2 ) 2 N 3 ( PF 6 )

Inelastic neutron scattering on deuterated single-crystal samples is used to study Haldane-gap excitations in the new S=1 one-dimensional quantum antiferromagnet NDMAP, that was recently recognized as an ideal model system for high-field studies. The Haldane gap energies

High-field phase diagram of the Haldane-gap antiferromagnet Ni(C5H14N2)2N3(PF6)

\Delta_x=0.42

Dynamics of an anisotropic Haldane antiferromagnet in a strong magnetic field

meV,