Takashi Tonegawa

Magnetic properties of the S = 1/2 distorted diamond chain at T = 0

We explore, at T = 0, the magnetic properties of the S = 1/2 antiferromagnetic distorted diamond chain described by the Hamiltonian = ? j = 1N/3{J 1 (S3j?1 ?S3j +S3j ?S3j+1)+J2S3j+1 ?S3j+2 +J3(S3j?2 ?S3j +S3j ?S3j+2)}?H ? l = 1NS lzwith J1, J2, J3 ? 0, which models well A3Cu3(PO4)4 with A = Ca, Sr, Bi4Cu3V2O14 and azurite Cu3(OH)2(CO3)2. We employ the physical consideration, degenerate perturbation theory, level spectroscopy analysis of the numerical diagonalization data obtained by the Lanczos method and also the density matrix renormalization group (DMRG) method. We investigate the mechanisms of the magnetization plateaux at M = Ms/3 and (2/3)Ms, and also show the precise phase diagrams of the (J2/J1,J3/J1) plane concerned with these magnetization plateaux, where M = ? l = 1NS lz and Ms is the saturation magnetization. We also calculate the magnetization curves and the magnetization phase diagrams by means of the DMRG method.

Magnetic properties of the diamond chain compound Cu3(CO3)2(OH)2

Azurite (Cu 3 (CO 3 ) 2 (OH) 2 ) is a model substance of a diamond spin chain, one of frustrated antiferromagnetic quantum spin chains. The high field magnetization up to 60 T, magnetic susceptibility, magnetic entropy, muon spin relaxation and 1 H-NMR of azurite have been measured using single crystals. A distinct 1/3 magnetization plateau is confirmed to be present in the magnetization curve. Two resonance peaks of 1 H-NMR. were observed. By analyzing temperature dependencies of their hyperfine shift. we found two different local susceptibilities which correspond to susceptibility of dimer and monomer spins, respectively. New field induced phase transition was found to occur at a critical field where the magnetic plateau onsets. A short range magnetic ordering developed in a peculiar two-stage process, which was revealed by temperature dependence of the magnetic specific heat and susceptibility.

Fractional S z excitation and its bound state around the 1/3 plateau of the S = 1 / 2 Ising-like zigzag XXZ chain

We present the microscopic view for the excitations around the 1/3 plateau state of the Ising-like zigzag

1/3 magnetization plateau in a one-dimensional anisotropic ferrimagnet

mathrm{XXZ}

Quantum magnetization plateau of an anisotropic mixed spin chain

chain. We analyze the low-energy excitations around the plateau with the degenerating perturbation theory from the Ising limit, combined with the Bethe-form wave function. We then find that the domain-wall particles carrying

Ground state phase diagrams of an anisotropic spin-12 Δ-chain with ferro- and antiferromagnetic interactions

{S}^{z}=ifmmodepmelsetextpmfi{}1/3

Ground-state phase diagram of an (S, S') = (1, 2) spin-alternating chain with competing single-ion anisotropies

and its bound state of

Magnetization process of the S=1/2 distorted diamond spin chain with the Dzyaloshinsky-Moriya interaction

{S}^{z}=ifmmodepmelsetextpmfi{}2/3

Two-step Quantum Spin Flop Transition in Spin Ladders

describe well the low-energy excitations around the 1/3 plateau state. The formation of the bound state of the domain walls clearly provides the microscopic mechanism of the cusp singularities and the even-odd behavior in the magnetization curve.

ELEMENTARY EXCITATIONS AND SPIN DYNAMICS IN NANOWIRE QUANTUM MAGNETS

Using mainly numerical methods, we investigate the ground-state magnetization curve of a mixed spin chain with uniaxial single-ion anisotropies, where S = 1 and S = 2 spins are alternating and coupled antiferromagnetically. Special attention is paid to the magnetization plateau, the 1/3-plateau, which appears at one third of the saturation magnetization in the magnetization curve. It is found that there appear three kinds of 1/3-plateaux, one of which has a quantum nature, while the remaining two have a classical (Ising) nature.