Norikazu Todoroki

Theory of ferroelectric phase transition in SrTiO 3 induced by isotope replacement

A theory to describe the dielectric anomalies and the ferroelectric phase transition induced by oxygen isotope replacement in

Ordered Phases and Phase Transitions in The Stacked Triangular Antiferromagnet CsCoCl3 and CsCoBr3

{\mathrm{SrTiO}}_{3}

Partial Disordered Phase of Ising Spin System in Distorted Triangular Lattice RbCoBr3

is developed. The proposed model gives consistent explanation between apparently contradictory experimental results on macroscopic dielectric measurements and microscopic lattice dynamical measurements by neutron-scattering studies. The essential feature is described by a three-state quantum order-disorder system characterizing the degenerated excited states in addition to the ground state of

Phase Diagram of Lattice–Spin System RbCoBr3

{\mathrm{TiO}}_{6}

Quantum-Fluctuation-Enhanced Ordered Phase in Blume–Capel Model

cluster. The effect of isotope replacement is taken into account through the tunneling frequency between the excited states. The dielectric properties are analyzed by the mean-field approximation (MFA), which gives qualitative agreements with the experimental results throughout full range of the isotope concentration. The phase diagram in the temperature-tunneling frequency coordinate is studied by a quantum Monte Carlo method to confirm the qualitative validity of the MFA analysis.

Generarized Cubic Model for BaTiO3-like Ferroelectric Substance

We study the ordered phases and the phase transitions in the stacked triangular antiferromagnetic Ising (STAFI) model with strong interplane coupling modeling CsCoCl 3 and CsCoBr 3 . We find that t...

Sublattice asymmetric reductions of spin values on stacked triangular lattice antiferromagnet CsCoBr3

Powder and single-crystal neutron diffraction measurements were performed on RbCoBr 3 . The magnetic phase transitions of this compound are well explained by the Ising spin model for a distorted triangular lattice. Magnetic peaks of powder diffraction patterns at 34 and 20 K closely fit a partial disordered phase and a ferrimagnetic phase, respectively. The temperature dependences of the ( h , h ,1) scan profile and magnetic Bragg peak heights at (1,1,1), (1/3,1/3,1), and (2/3,2/3,1) were measured for a single-crystal sample. We conclude that the ferrimagnetic phase only exists below 30.5 K. The partial disordered phase is identified between 30.5 (= T N2 ) and 37.2 K (= T N1 ). We found a characteristic linear increase in the (1,1,1) peak height below T N2 with decreasing temperature. These results show that a lattice distortion couples to the spin system. Numerical simulations are also performed to estimate magnetic interaction parameters.

Ordered phase and phase transitions in the three-dimensional generalized six-state clock model

We study the lattice–spin model of RbCoBr 3 which is proposed by Shirahata and Nakamura, by mean field approximation. This model is an Ising spin system on a distorted triangular lattice. There are two kinds of frustrated variables, that is, the lattice and spin. We obtain a phase diagram of which phase boundary is drawn continuously in a whole region. Intermediate phases that include a partial disordered state appear. The model has the first-order phase transitions in addition to the second-order phase transitions. We find a three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice ferrimagnetic state does not appear when the lattice is not distorted.We study the lattice-spin model of RbCoBr

Theory of ferroelectric phase transition in SrTiO3 induced by isotope replacement

_3

Partial Disordered Phase of Ising Spin System in Distorted Triangular Lattice RbCoBr_3(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

which is proposed by Shirahata and Nakamura, by mean field approximation. This model is an Ising spin system on a distorted triangular lattice. There are two kinds of frustrated variables, that is, the lattice and spin. We obtain a phase diagram of which phase boundary is drawn continuously in a whole region. Intermediate phases that include a partial disordered state appear. The model has the first-order phase transitions in addition to the second-order phase transitions. We find a three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice ferrimagnetic state does not appear when the lattice is not distorted.