Masashi Fujisawa

Neutron Diffraction Study of the Pressure-Induced Magnetic Ordering in the Spin Gap System TlCuCl3

Neutron elastic scattering measurements have been performed under a hydrostatic pressure in order to investigate the spin structure of the pressure-induced magnetic ordering in the spin gap system TlCuCl 3 . Below the ordering temperature T N =16.9 K for the hydrostatic pressure P =1.48 GPa, magnetic Bragg reflections were observed at reciprocal lattice points Q =( h , 0, l ) with integer h and odd l , which are equivalent to those points with the lowest magnetic excitation energy at ambient pressure. This indicates that the spin gap closes due to the applied pressure. The spin structure of the pressure-induced magnetic ordered state for P =1.48 GPa was determined.

Electric Polarization Induced by Néel Order without Magnetic Superlattice: Experimental Study of Cu3Mo2O9 and Numerical Study of a Small Spin Cluster

We clarify that the antiferromagnetic order in the distorted tetrahedral quasi-one-dimensional spin system induces electric polarization. In this system, the effects of low dimensionality and magnetic frustration are expected to appear simultaneously. We obtain the magnetic-field–temperature phase diagram of Cu 3 Mo 2 O 9 by studying the dielectric constant and spontaneous electric polarization. Around the tricritical point at 10 T and 8 K, the change in the direction of electric polarization causes a colossal magnetocapacitance. We calculate the charge redistribution in a small spin cluster consisting of two magnetic tetrahedra to demonstrate the electric polarization induced by the antiferromagnetism.

Electron spin resonance studies of P and B codoped Si nanocrystals

P- and/or B-doped Si nanocrystals (Si-ncs) embedded in glass matrices were studied by electron spin resonance (ESR) spectroscopy to investigate the origin of strong room-temperature photoluminescence (PL) of n- and p-type impurities codoped Si-ncs below the band-gap energy of bulk Si crystals. It was shown that the intensity and width of the ESR signal depend strongly on impurity concentrations. A clear correlation was observed between the ESR signal width and the PL intensity. The observed correlation suggests that in addition to the geometrical confinement, P and B codoping further localize carriers in Si-ncs, and the strong localization results in the characteristic luminescence properties.

Pressure-induced Magnetic Quantum Phase Transition from Gapped Ground State in TlCuCl3

Magnetization measurements under hydrostatic pressure were performed on an S =1/2 coupled spin dimer system TlCuCl 3 with a gapped ground state under magnetic field H parallel to the [201] direction. With increasing applied pressure P , the gap decreases and closes completely at P c = 0.42±0.05 kbar. For P > P c , TlCuCl 3 undergoes antiferromagnetic ordering. A spin-flop transition was observed at H sf ≃0.7 T. The spin-flop field is approximately independent of pressure, although the sublattice magnetization increases with pressure. The gap and Neel temperature are presented as functions of pressure. The occurrence of the pressure-induced quantum phase transition is attributed to the relative enhancement of the interdimer exchange interactions compared with the intradimer exchange interaction.

Magnetic ordering under high pressure in the quantum spin system TlCuCl3

Abstract TlCuCl3 is a strongly coupled spin dimer system with the excitation gap Δ/k B =7.7 K . It was found that the gap decreases rapidly at pressures around P=0.2 GPa and the magnetic ordering arises for P>0.4 GPa . The phase diagram for the magnetic field parallel to the [2 0 1] direction obtained at P=0.74 GPa is presented.

Neutron scattering study of magnetic ordering and excitations in the doped spin-gap system Tl ( Cu 1 − x Mg x ) Cl 3

Neutron elastic and inelastic scattering measurements have been performed in order to investigate the spin structure and the magnetic excitations in the impurity-induced antiferromagnetic ordered phase of the doped spin gap system

Pressure-Induced Magnetic Quantum Phase Transition in Gapped Spin System KCuCl3

\mathrm{Tl}({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}){\mathrm{Cl}}_{3}

Recent developments of high field ESR systems in Kobe

with

High-field ESR measurements of S=3/2 honeycomb lattice antiferromagnet Bi3Mn4O12(NO3)

x=0.03.

High-Field ESR Measurements of S=1/2 Kagome Lattice Antiferromagnet BaCu3V2O8(OH)2

The magnetic Bragg reflections indicative of the ordering were observed at