Yoichi Nishiwaki

Dielectric and Magnetic Properties of the Distorted Triangular Lattice Ising-Like Antiferromagnet TlCoCl3

Successive structural phase transitions with ferroelectricity were found in TlCoCl 3 through dielectric constant measurements and D – E hysteresis loop observations. The sequence of the transitions is identical with that in RbMnBr 3 and TlFeCl 3 , which undergo successive transitions from the prototype crystal structure of CsNiCl 3 . The temperature dependence of the magnetic susceptibility below T N1 indicates the presence of successive magnetic orderings, which has not been observed in the Ising-like antiferromagnets CsCoCl 3 and CsCoBr 3 without structural transitions. Dielectric dispersion attributable to the Ising-spin dynamics on a linear-chain spin system was observed at low temperatures. Several problems to be solved are proposed for understanding structural and magnetic properties of TlCoCl 3 .

Neutron Diffraction Study of Distorted-Triangular-Lattice Ising-like Antiferromagnet RbCoBr3

A powder and single-crystal neutron diffraction study was performed on the structural and magnetic phase transitions of the distorted-triangular-lattice Ising-like antiferromagnet TlCoCl 3 . From the results of powder sample measurement, the crystal structures were identified as the P 6 3 c m and P b c a structures at the intermediate-temperature (75 < T < 165 K) and lowest-temperature ( T <68 K) phases, respectively. From the results of single-crystal measurement, it was clarified that Ising spins were arranged in an up-up-down-down manner with a triple-domain formation below the Neel temperature. Satellite peaks on the shoulder of magnetic peaks were observed near the Neel temperature.

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

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.

Magnetic and Dielectric Properties of RbCoBr3 Inspected from Nonmagnetic Impurity Effect

Through magnetic and dielectric measurements, a simultaneous phase transition of spin and lattice systems observed previously at 37.2 K of RbCoBr 3 have been investigated by doping with nonmagnetic Mg impurities. A mutual reduction in the ferroelectric Curie temperature T C and the Neel temperature T N due to the enhancement of Mg doping confirms the occurrence of the synergistic ordering of both. A broad peak of the real part of dielectric constant along the c axis, e ′ c ( T ), at approximately 32 K of the pure system splits into two sharp peaks in mixed systems. This suggests the presence of successive structural phase transitions at around this temperature. A probable sequence of crystal and magnetic structures was discussed for the successive phase transitions of RbCo 1- x Mg x Br 3 . The interplay between the spin and lattice variables of RbCoBr 3 was interpreted by taking account of spin-dependent polarizability and spin-dependent spontaneous polarization. A dielectric anomaly observed at 9.0 K in ...

Phase Diagram of Lattice–Spin System RbCoBr3

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

Polarized Neutron Inelastic Scattering Study of Anisotropic Magnetic Fluctuations in Quasi-One-Dimensional Ising-like Antiferromagnet TlCoCl3

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Magnetic Excitations in the Quasi-1D Ising-like Antiferromagnet TlCoCl3

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.

Thermal Expansion and Dielectric Properties of Triangular Lattice Antiferromagnet RbCoBr3

Polarized neutron inelastic scattering experiments have been carried out in the quasi-1D Ising-like antiferromagnet TlCoCl 3 . We observed the longitudinal magnetic fluctuation S z z ( Q , ω) for t...

Neutron Diffraction Study of Successive Magnetic Phase Transitions of Distorted-Triangular-Lattice Antiferromagnet RbFeBr3

Neutron inelastic scattering measurements have been performed in order to investigate the magnetic excitations in the quasi-1D Ising-like antiferromagnet TlCoCl

Spin-lattice model of magnetoelectric transitions in RbCoBr3

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