Zentarou Honda

Inducing a magnetic ordering in the Haldane material Ni() by magnetic field

From a heat capacity measurement in high magnetic fields and at low temperatures, we have obtained evidence for a magnetic ordering in the S = 1 quasi-one dimensional Heisenberg antiferromagnet . The transition temperature is at 12 T parallel to the chain axis.

Inducing a magnetic ordering in the Haldane material Ni(C5H14N2)2N3(C1O4) by magnetic field

Due to an oversight, the last page of this article (L88) containing references [8 - 16] was not printed. The missing references are reproduced below. [8] Kobayashi T, Tabuchi Y, Amaya K, Ajiro Y, Yosida T and Date M 1992 J. Phys. Soc. Japan 61 1772 [9] Mitra P P and Halperin B I 1994 Phys. Rev. Lett. 72 912 [10] Sakai T and Shiba H 1994 J. Phys. Soc. Japan 63 867 [11] Sieling M, Palme W and Luthi B1995 Z. Phys. B 96 297 [12] Brill T M, Boucher J P, Brunel L C, Renard J P and Verdaguer M 1995 Physica B 204 303 [13] Yamashita M, Inoue K, Ohishi T, Takeuchi T, Yosida T and Mori W 1995 Mol. Cryst. Liq. Cryst. 274 25 [14] Renard J P, Verdaguer M, Regnault L P, Erkelens W A C, Rossat-Mignod J and Stirling W G 1987 Europhys. Lett. 3 945 [15] Yamamoto S and Miyashita S 1993 Phys. Rev. B 48 9528 [16] Fujiwara N, Goto T, Maegawa S and Kohmoto T 1993 Phys. Rev. B 47 11860

High field magnetization and multi-frequency ESR in the spin-ladder compound Na2Fe2(C2O4)3(H2O)2

We have performed high field magnetization and multi-frequency electron spin resonance (ESR) measurements on single crystal and powder samples of Na2Fe2(C2O4)3(H2O)2, abbreviated as SIO. The Fe2+ ions in SIO are bridged by oxalate groups to make two-leg ladders. The temperature dependence of magnetic susceptibilities parallel and perpendicular to the leg direction show very different and anisotropic behavior. Experimental results of the isomorphous compound Na2Co2(C2O4)3(H2O)2 (SCO) are well explained by isolated magnetic dimers with an Ising-type anisotropy. Therefore, we analyze the frequency dependence of the ESR resonance fields by the same model with a fictitious spin 1 as in SCO. The agreement between experiment and calculation is satisfactorily good. Magnetic susceptibility and magnetization curves calculated with the same parameters obtained in the ESR analyses, however, do not agree well with the experimental ones. This indicates the presence of the exchange interaction between the dimers, namely the interaction along the leg.

Magneto-Transport Study on Ni1-xMnx(0.23<x<0.3) in High Fields up to 30T

Giant negative magnetoresistance (MR) up to 15 % were observed for nano-scaled grains of Ni1-xMnx(0.23<x<0.3) in high fields up to 30 T. The crystal grain size (≈5nm) was obtained by an adequate annealing condition of 630 K, 200hrs. The sample resistance decreased linearly with magnetization increases in each magnetization range for different x, and decreased with the same slope even for different x. The observed negative MR is plausibly explained by the scattering of carriers by the anti-parallel spin pairs of residual Mn-Mn clusters.

An electron spin resonance study of magnetic excitations in the quantum antiferromagnet Ni(C5H14N2)2N3(PF6)

We report the results of electron spin resonance (ESR) measurements on single crystals of the spin 1 quasi-one-dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6) in the high-field phase. We observed ESR transitions from the ground state with a q=π component above the critical field Hc. The experimental results are analyzed using the energy level scheme that is widely accepted for the spin 1 one-dimensional Heisenberg antiferromagnet below Hc.

Phthalocyanine based metal containing porous carbon sheet

Highly-ordered fused-ring poly copper phthalocyanine (PCuPc) was prepared using copper octacyanophthalocyanine as a building block, and two-dimensional (2D) square superlattices were directly observed by the transmission electron microscopy. Remarkably, we have found a formation of polymer network that consists of a 2D porous PCuPc sheet in which the centers of phthalocyanine units are alternately occupied by Cu atom and vacancy. Using this “half-filling” PCuPc, it must be possible to create alternating arrangements for transition metal centers, and therefore control the magnetic properties of the 2D carbon sheets.

Multi-frequency ESR in the haldane magnet NDMAP below 1 K

The S=1 quasi-one dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6), abbreviated as NDMAP, has been studied by electron spin resonance (ESR) in a magnetic field exceeding the critical field (Hc) above which this compound shows a long range order (LRO) at sufficiently low temperatures. Our recently developed ESR apparatus with a dilution refrigerator is utilized to study the spin excitations of NDMAP above Hc for H∥c, because this compound exhibits the LRO below about 1 K. The spin excitation modes above Hc observed below 1 K do not show any difference from those at 1.5 K and the lowest excitation mode observed at 30 mK in the inelastic neutron experiments above Hc was not observed at about 200 mK in this study. Accordingly, the result suggests that the lowest excitation mode is very sensitive to temperature.

New development of sensitive magnetic sensors for nondestructive evaluation of structural materials

The diagnosis of iron-based materials was performed by using many magnetic sensors such as a small Hall element for leakage flux observations after polarizations, a locally sensitive fluxgate sensor available down to 100pT, by a pick-up coil for magnetic noise observation and by a triple-fold coil for eddy current detector. The spatially high resolution of the magnetic sensors was attained as narrow as 100 μm or less with the same order lift-off distance depending on the situation. By using these detectors, we detected the positions with the relatively high stress in comparison with the other positions. Residual stress detection less than 0.1 % in ferromagnetic material was attained in this study by deriving the expectations of field strength for magnetic noise occurrence. Positions with small holes inside the material were precisely detected by an eddy current detector, composed of a triple-fold coil with thin amorphous ribbon and attached from the material surface. The small magnetic field emission from a new type flux gate sensor was also attained by composing a double coil set for flux gate with the opposite coil current coil each other.

Field induced spin transitions and large magnetoresistance in the quasi-one-dimensional magnet Ca/sub 3/Co/sub 2/O/sub 6/

The Co spin states on trigonal prisms and octahedral were clarified, and the large magnetoresistance during phase transitions induced by externally applied fields was obtained. The magnetic susceptibility of Ca/sub 3/Co/sub 2/O/sub 6/ single crystals were measured for varying temperatures. A second magnetic transition was observed to occur at T/sub c2/=12 K. Results reveal an intra-chain ferromagnetic ordering at T/sub c1/=23 K and a weak antiferromagnetic inter-chain coupling at T/sub c2/=12 K. The field induced phase transition from a ferrimagnetic to ferromagnetic state and the prominent magnetic hysteresis suggests that the sample behaves as an Ising-like antiferromagnetic triangular lattice.

Magnetic Diagnosis of Structural Materials and These Monte-Carlo Simulations

Many magnetic techniques were developed for nondestructive evaluations for iron-based materials such as SUS304, A533B, S25C etc in a tensile stress range up to each fracture state. Magnetic tools are composed of a triple-fold coil for ac resistivity detections, a small Hall element for leakage flux observations after polarizations of the material and a pickup coil of magnetic Barkhausen noises combined with the excitation yoke. The degree of degradations was expressed by an average field for the discontinuous magnetization. Magnetic noises were simulated by Monte-Carlo method under the non-equilibrium condition with limited trials.