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Aiming at nondestructive evaluation of magnetic materials, Monte Carlo simulations of the dynamic magnetic processes were investigated on the temporal and the temperature dependences for spin systems with various lattice imperfections as so called Barkhausen noises. From a physical point of view, the presented method might be the more useful tool for the analyses of the dynamic magnetic processes rather than those by Preisach model. We have been investigated on the Nondestructive Evaluations (NDE) of iron-based structural materials by detecting the magnetic property changes with increasing fatigues. Therefore, the observations of magnetic properties have been expected as a diagnosis method for NDE. For these purposes of NDE, many researchers have been studied on the magnetic properties of structural materials (1-9). Figure 1 shows an example of experimentally observed Barkhausen Noises (BN) spectra at a sample position as a function of applied field up to 14 mT with different yoke angles against the sample elongation direction for an iron-based material (A533B) with a residual stress caused by a tensile stress of 600 MPa. The alphabets in this figure indicated by "a"-"l" stand for the different yoke angle directions against the sample elongating direction. The spectrum of "g" was observed with a magnetic yoke pair (N-S) configuration in the perpendicular direction against the long sample. Here, the spectra of "a" and "l" stand for the observations in the parallel direction with the sample. As it is apparently seen, the BN spectra show large dependences on the observed yoke directions. Further, experimental results vary with the complicated combinations of the observing positions, angles, sample shape, preparations, annealing conditions, sample history, ambient temperatures and the chemical compositions. The microscopic processes and the method of the analyses for BN, therefore, have not been sufficiently studied due to this complexity. The difficulty of BN analysis seems to be cause by the dynamic process including localized magnetic potentials and by the transient de-pinning processes. By these reasons, the itinerant model could not be adopted for these analyses. The Preisach model is neither applicable because the total M-H curves are composed of many miner loops describing the steady states even though dM/dH at each point could be defined. In this paper, we developed a special Monte-Carlo (MC) method with

Fe-Si alloy system was investigated on the magneto-resistance (MR) effects in a temperature range between 77K-RT and in high fields up to 30 T. The samples were prepared by sputtering Fe(200 nm) on n-Si(1 0 0) surface and variously annealed up to beta-FeSi2 are obtained. The MR effects were found small less than several %, negative at RT and positive at T=77 K for Fe-rich samples. For a sample at the stoichiometric beta-Fe-Si-2 on n-Si as a p-n junction, we found a positive MR as large as 30% at RT in B = 30 T. The physical mechanism of the large MR is tentatively given by the carrier freeze-out effect in between the p-n. (c) 2006 Elsevier B.V. All rights reserved.

Giant negative magnetoresistance (MR) up to 15 % were observed for nano-scaled grains of Ni1-xMnx(0.23

Magnetic and magnetoresistance effect of needle shaped crystal and slightly Co rich Ca3Co2O6 was investigated in a temperature range between 2 and 100 K and in a dc magnetic field range less than 7 T and in pulsed fields less than 20 T. We found 1/3m(s) and 2/3m(s) plateaus of the magnetization for the full magnetization m, and large negative magnetoresistance effect of 10% at the same magnetic fields, respectively. (c) 2006 Elsevier B.V. All rights reserved.

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.

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.

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.

We have performed a heat capacity (Cp) measurement using a relaxation method on a single-crystal sample of the S = 1 quasi-one-dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(ClO4) in high magnetic fields and at low temperatures. An anomaly in Cp has been observed at about 0.9 K and at 12 T. We interpret this anomaly as an indication of field induced long-range magnetic ordering.

A series of compounds, [Ni(AA)2X]Y (AA=diamines, tetramines etc; X=N 3 − and NO 2 − ; Y=ClO 4 − , PF 6 − etc) with S=1 have been synthesized, and their magnetic properties and crystal structures have been investigated. They have linear-chain structures. It has been found that the magnitude of the Haldane gaps can be controlled by substituting the bridging groups(X) and in-plane ligands(AA). On the other hand, [Ni([15]aneN 4 )N 3 ]PF 6 , [Ni([14]aneN 4 )N 3 ]ClO 4 ·H 2 O and [Ni(en) 2 NO 2 ]BF 4 show spin glass behaviors.

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