Masato Hagihala

Antiferromagnetism and geometric frustration in tetrahedral lattice hydroxyhalides M2(OH)3X

A systematic study of magnetic susceptibility measurements is carried out on distorted tetrahedral lattice hydroxyhalides Fe2(OH)3Cl, Mn2(OH)3Cl, Mn2(OH)3Br, and Co2(OH)3Br, following our recent finding of coexisting antiferromagnetic order and disorder in Cu2(OH)3Cl (clinoatacamite). These transition metal hydroxyhalides are found to undergo antiferromagnetic transitions, at TN = 14 K for Fe2(OH)3Cl, at two successive transitions of TN1 = 3.4 K and TN2 = 2.7 K for Mn2(OH)3Cl, at TN1 = 3.3 K and TN2 = 2.4 K for Mn2(OH)3Br, and at TN = 5 K for Co2(OH)3Br, respectively. All hydroxychlorides show coexisting glassiness below the magnetic transitions; meanwhile, the glassiness is not found in the hydroxybromides. The distorted tetrahedral lattice for the magnetic ions consists of stacked layers of triangular lattice planes and Kagome lattice planes, with the magnetic ions on the Kagome lattice planes being bonded by the halogen ions. The contrasting behaviours in Mn2(OH)3Cl and Mn2(OH)3Br suggest that the glassiness arises from competing magnetic interactions in the tetrahedron, specifically on the Kagome lattice planes.

Spin Density Wave in Insulating Ferromagnetic Frustrated Chain LiCuVO4

We study a field-induced quantum phase in the weakly-coupled ferromagnetic frustrated chain LiCuVO 4 by a neutron diffraction technique. A new incommensurate magnetic peak is observed at H ≥8.5 T. The field-dependent propagation vector is identified with the spin density wave correlation in the theoretically predicted magnetic quadrupole order. Quantum fluctuation, geometrical frustration, and interchain interaction induce an exotic spin density wave long-range order in the insulating magnet.

Spin-Liquid Ground State in the Spin 1=2 Distorted Diamond Chain Compound K3Cu3AlO2(SO4)4

The new compound K3Cu3AlO2(SO4)4, representing a spin 1/2 distorted diamond chain system, was synthesized and its magnetic properties were studied by magnetic susceptibility, specific heat, and high-field magnetization measurements. Magnetic Cu2+ ions were found to form a highly one-dimensional distorted diamond chain with strong intrachain interactions. Short-range magnetic correlations were observed to develop in a two-stage process without magnetic long-range ordering by magnetic susceptibility and specific heat measurements. The exchange constant ratio J2/J1, where J2 is the magnetic interaction of the diamond backbone and J1 is the magnetic interaction of the monomers along the chain, was estimated to be 2.5, demonstrating that the magnetic ground state is composed of an alternating dimer–monomer spin-liquid phase. The absence of an M = 0 plateau in the high-field magnetization curve is also consistent with an alternating dimer–monomer model. These results strongly suggest that K3Cu3AlO2(SO4)4 is the...

NMR Study of Spin State in Geometrically Frustrated Compound Co2Cl(OH)3

NMR studies of a geometrically frustrated system, Co 2 Cl(OH) 3 , are carried out at low temperature. The NMR results of 59 Co and 1 H nuclei show that long-range ordered ferromagnetic moments on the triangular lattice plane coexist microscopically with disordered moments on the kagome lattice plane. The moment direction is not ordered. Although the disordered moments freeze within the NMR observation time (10 -4 s) at low temperature, the frozen moments begin to fluctuate with increasing temperature. Up to 4.2 K (0.4 T C ), the magnitude of the ferromagnetically ordered moments is independent of temperature.

Long-Time Variation in Magnetic Structure of CeIr3Si2: Observation of a Nucleation-and-Growth Process of Magnetic Domains

CeIr3Si2 is the first three-dimensional uniform magnet in which the long-time variation in magnetic structure was observed. To clarify the microscopic mechanism of this magnetic structural change, time-resolved neutron scattering measurements have been reinvestigated. Clear time variations in the line widths as well as the amplitudes of magnetic Bragg diffractions have been observed in this improved instrumentation. On the basis of this observation, a nucleation-and-growth model of magnetic structural change has been presented. The numerical calculation with this model reproduces well the observation.

Unusual low-temperature phase in VO2 nanoparticles

We present a systematic investigation of the crystal and electronic structures and the magnetic properties above and below the metal-insulator transition of ball-milled

Mid-IR and Raman Spectral Properties of Clinoatacamite-Structure Basic Copper Chlorides

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Proton NMR Study of Atacamite Cu2Cl(OH)3

nanoparticles and

Proton NMR Study of Pyrochlore-Like Atacamite Mn2Cl(OH)3

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Magnetic State Selected by Magnetic Dipole Interaction in Kagome Antiferromagnet NaBa

microparticles. For this research, we performed a Rietveld analysis of synchrotron radiation x-ray diffraction data,