Zigzag Spin Chain Research Articles

Magnetic Phase Diagram of theS=1/2 Antiferromagnetic Zigzag Spin Chain in the Strongly Frustrated Region: Cusp and Plateau

We determine the magnetic phase diagram of the antiferromagnetic(AF) zigzag spin chain in the strongly frustrated region, using the density matrix renormalization group method. We find the magnetization plateau at 1/3 of the full moment accompanying the spontaneous symmetry breaking of the translation, the cusp singularities above and/or below the plateau, and the even-odd effect in the magnetization curve. We also discuss the formation mechanisms of the plateau and cusps briefly.

Magnetization and specific heat of a ferromagnetic zigzag spin chain compound LaCrOS 2

The magnetization and the specific heat of an oxysulfide LaCrOS 2, in which Cr ions form zigzag spin chains, have been measured. The temperature dependence of the magnetic susceptibility deviates from the Curie–Weiss behavior with the Weiss temperature Θ p =66 K, below 200 K. A peak appears in the low field susceptibility vs. temperature curve at 32 K, which is regarded to signal the ferromagnetic transition. The temperature dependence of the magnetic specific heat shows a broad maximum, which is characteristic of a low dimensional magnetic system. In addition, a small sharp peak is observed at 32 K which is attributed to the three-dimensional ferromagnetic transition. These behaviors are well explained by an effective Ising spin chain model for S=3/2 with a weak interchain interaction.

Mean field theory on the incommensurate ground state of the zigzag spin chain

We give a mean field treatment of the incommensurate phase of the zigzag spin-1/2 Heisenberg chain containing both the nearest neighbour coupling J 1 and the next nearest neighbour antiferromagnetic coupling J 2. By use of Jordan–Wigner transformation, the zigzag spin chain is mapped into an interacting spinless fermionic system with two pairs of Fermi points. The incommensurate ground state commences when one more Fermi sea begins to be filled. The mean field theory predicts a new critical point in the ferromagnetic region x c =−2( π+1)/( π−1) such that the system is incommensurate in region x c < J 1/ J 2<2. We conjecture that the ground state in the region x c > J 1/ J 2>−4 has a nonzero total spin magnitude instead of four Fermi points.

Strongly reduced gap in the zigzag spin chain with a ferromagnetic interchain coupling

We study a spin 1/2 Heisenberg zigzag spin chain model near decoupled two chains. Taking into account a symmetry breaking perturbation, we discuss the existence of an energy gap in the ferromagnetic interchain coupling as well as the antiferromagnetic one. In the ferromagnetic model, a marginally relevant fixed line reduces the gap strongly, so that the correlation length becomes an astronomical length scale even in order 1 coupling. This result agrees with density matrix renormalization group results.

Antiferromagnetic zigzag spin chain in magnetic fields at finite temperatures

We study thermodynamic behaviors of the antiferromagnetic zigzag spin chain in magnetic fields, using the density-matrix renormalization group method for the quantum transfer matrix. We focus on the thermodynamics of the system near the critical fields in the ground-state magnetization process($M$-$H$ curve): the saturation field, the lower critical field associated with excitation gap, and the field at the middle-field cusp singularity. We calculate magnetization, susceptibility and specific heat of the zigzag chain in magnetic fields at finite temperatures, and then discuss how the calculated quantities reflect the low-lying excitations of the system related with the critical behaviors in the $M$-$H$ curve.

NMR Studies on Spin-Gap Behavior of Monoclinic CuNb2O6

The NMR Knight shift and the spin-lattice relaxation rate 1/ T 1 have been measured at Nb sites in two polymorphs of quasi one-dimensional zig-zag spin chain compounds CuNb 2 O 6 . The temperature ( T ) dependence of NMR-1/ T 1 of the monoclinic CuNb 2 O 6 indicates the existence of spin excitation gap (spin gap) whose magnitude (∼20 K) is consistent with the result of other kinds of measurements. The difference of the T -dependences between 1/ T 1 T and K is similar to that well-known for high- T c oxides. A simultaneous growing of the antiferromagnetic and the singlet correlation has been observed with decreasing T at around the temperature of the susceptibility maximum (≥20 K). Results of the NMR measurements for the orthorhombic CuNb 2 O 6 , which undergoes an antiferromagnetic transition at about 7.3 K, are also presented.

Spin-Gap Behavior of CuNb2O6

The magnetic properties of two polymorphs of CuNb 2 O 6 with quasi-one-dimensional zig-zag spin ( S =1/2) chains of Cu 2+ ions are studied. The magnetic excitation spectra of Cu spins measured by neutron scattering, and the T -dependence of the longitudinal spin relaxation rate of 93 Nb nuclei by NMR indicate the existence of the spin gap in the monoclinic phase whose magnitude is consistent with the one deduced by the detailed analyses of uniform magnetic susceptibility at low temperatures. The behavior in the monoclinic phase is in clear contrast to that found in the orthorhombic phase.

Dimerization and incommensurate spiral spin correlations in the zigzag spin chain: Analogies to the Kondo lattice.

Using the density matrix renormalization group and a bosonization approach, we study a spin-1/2 antiferromagnetic Heisenberg chain with near-neighbor coupling ${\mathit{J}}_{1}$ and frustrating second-neighbor coupling ${\mathit{J}}_{2}$, particularly in the limit ${\mathit{J}}_{2}$\ensuremath{\gg}${\mathit{J}}_{1}$. This system exhibits both dimerization and incommensurate spiral spin correlations. We argue that this system is closely related to a doped, spin-gapped phase of the one-dimensional Kondo lattice. \textcopyright{} 1996 The American Physical Society.