Tokuro Shimokawa

Collapse of Ferrimagnetism in Two-Dimensional Heisenberg Antiferromagnet due to Frustration

We study ferrimagnetism in the ground state of the antiferromagnetic Heisenberg model on the spatially anisotropic kagome lattice, in which ferrimagnetism of the conventional Lieb–Mattis type appears in the region of weak frustration whereas the ground state is nonmagnetic in the isotropic case. Numerical diagonalizations of small finite-size clusters are carried out to examine the spontaneous magnetization. We find that the spontaneous magnetization changes continuously in the intermediate region between conventional ferrimagnetism and the nonmagnetic phase. Local magnetization of the intermediate state shows strong dependence on the site position, which suggests non-Lieb–Mattis ferrimagnetism.

Quantum Spin-Liquid Behavior in the Spin-1/2 Random-Bond Heisenberg Antiferromagnet on the Kagome Lattice

The effect of the quenched bond-randomness on the ordering of the

Ferrimagnetism of the Heisenberg Models on the Quasi-One-Dimensional Kagome Strip Lattices

S=1/2

Frustration-Induced Ferrimagnetism in S = 1/2 Heisenberg Spin Chain

antiferromagnetic Heisenberg model on the kagome lattice is investigated by means of an exact-diagonalization method. When the randomness exceeds a critical value, the ground state of the model exhibits a transition within the non-magnetic state into the randomness-relevant gapless spin-liquid state. Implications to the S=1/2 kagome-lattice antiferromagnet herbertsmithite is discussed.

Fine-Tuning of Magnetic Interactions in Organic Spin Ladders

We study the ground-state properties of the S =1/2 Heisenberg models on the quasi-one-dimensional kagome strip lattices by the exact diagonalization and density matrix renormalization group methods. The models with two different strip widths share the same lattice structure in their inner part with the spatially anisotropic two-dimensional kagome lattice. When there is no magnetic frustration, the well-known Lieb–Mattis ferrimagnetic state is realized in both models. When the strength of magnetic frustration is increased, on the other hand, the Lieb–Mattis-type ferrimagnetism is collapsed. We find that there exists a non-Lieb–Mattis ferrimagnetic state between the Lieb–Mattis ferrimagnetic state and the nonmagnetic ground state. The local magnetization clearly shows an incommensurate modulation with long-distance periodicity in the non-Lieb–Mattis ferrimagnetic state. The intermediate non-Lieb–Mattis ferrimagnetic state occurs irrespective of strip width, which suggests that the intermediate phase of the ...

Two-Dimensional Honeycomb Lattice Consisting of a New Organic Radical 2-Cl-6-F-V

The ground-state properties of the S = 1/2 frustrated Heisenberg spin chain with interactions up to fourth nearest neighbors are investigated by the exact-diagonalization method and density matrix renormalization group method. Our numerical calculations clarify that the ferrimagnetic state is realized in the ground state in spite of the fact that a multi-sublattice structure in the shape of the system is absent. We find that there are two types of ferrimagnetic phases: one is the well-known ferrimagnetic phase of the Lieb–Mattis type and the other is the nontrivial ferrimagnetic phase that is different from that of the Lieb–Mattis type. Our results suggest that a multi-sublattice structure of the shape is not necessarily required for the occurrence of ferrimagnetism.

Nontrivial ferrimagnetism of the Heisenberg model on the Union Jack strip lattice

We have succeeded in synthesizing two types of new organic radical crystals 3-I-V [= 3-(3-iodophenyl)-1,5-diphenylverdazyl] and 3-Br-4-F-V [= 3-(3-bromo-4-fluorophenyl)-1,5-diphenylverdazyl]. Their crystal strucutures are found to be isomorphous to that of previously reported spin ladder 3-Cl-4-F-V. Through the quantitative analysis of their molecular arrangements and magnetic properties, we confirm that these materials form ferromagnetic chain-based spin ladders with slightly modulated magnetic interactions. These results present the first quantitative demonstration of the fine-tuning of magnetic interactions in the molecular-based materials.We have succeeded in synthesizing two types of new organic radical crystals 3-I-V [= 3-(3-iodophenyl)-1,5-diphenylverdazyl] and 3-Br-4-F-V [= 3-(3-bromo-4-fluorophenyl)-1,5-diphenylverdazyl]. Their crystal strucutures are found to be isomorphous to that of previously reported spin ladder 3-Cl-4-F-V. Through the quantitative analysis of their molecular arrangements and magnetic properties, we confirm that these materials form ferromagnetic chain-based spin ladders with slightly modulated magnetic interactions. These results present the first quantitative demonstration of the fine-tuning of magnetic interactions in the molecular-based materials.

Exact diagonalization and cluster mean-field study of triangular-lattice XXZ antiferromagnets near saturation

We have successfully synthesized new organic radical crystals of 2-Cl-6-F-V [= 3-(2-chloro-6-fluorophenyl)-1,5-diphenylverdazyl]. Two types of dominant intermolecular interactions forming a honeycomb lattice are deduced from the molecular packing in the crystal, and ab initio molecular orbital calculation also indicate such an exchange network. We analyzed the magnetic and thermodynamic properties by using the quantum Monte Carlo method and successfully explained these properties as an \(S = 1/2\) Heisenberg honeycomb lattice with ferromagnetic chain interactions. Our results indicate that 2-Cl-6-F-V is one of the few examples of a purely organic radical compound that forms two-dimensional lattices, and this paper presents the first complete, quantitative description of an actual honeycomb lattice material.

Ferrimagnetism of the Heisenberg model on the Kagome strip lattice

We study the ground-state properties of the S = 1/2 antiferromagnetic Heisenberg model on the Union Jack strip lattice by using the exact-diagonalization and density matrix renormalization group methods. We confirm a region of a magnetization state intermediate between the Néel-like spin liquid state and the conventional ferrimagnetic state of a Lieb-Mattis type. In the intermediate state, we find that the spontaneous magnetization changes gradually with respect to the strength of the inner interaction. In addition, the local magnetization clearly shows an incommensurate modulation with long-distance periodicity in the intermediate magnetization state. These characteristic behaviors lead to the conclusion that the intermediate magnetization state is a non-Lieb-Mattis ferrimagnetic one. We also discuss the relationship between the ground-state properties of the S = 1/2 antiferromagnetic Heisenberg model on the original Union Jack lattice and those on our strip lattice.

Magnetization Curve of the Kagome-Strip-Lattice Antiferromagnet

Quantum magnetic phases near the magnetic saturation of triangular-lattice antiferromagnets with XXZ anisotropy have been attracting renewed interest since it has been suggested that a nontrivial coplanar phase, called the