Effects of Randomness on the Field-Induced Phase Transition in the S=1 Bond-Alternating Spin Chain NTENP

We report novel effects of randomness in the S=1 bond-alternating antiferromagnetic chain compound with a dimer-singlet ground state [Ni(N,N'-bis(3-aminopropyl)propane-1,3-diamine(mu-NO2]ClO4 abbreviated as NTENP. The 15N NMR spectra develop a continuum with sharply peaked edges at low temperatures, indicating an inhomogeneous staggered magnetization induced by magnetic field. We attribute this to random anisotropic interactions due to disorder of NO2 groups in the chains. The field-induced antiferromagnetic transition exhibits remarkably anisotropic behavior. We propose that a field-induced incoherent magnetization is transformed into a coherent antiferromagnetic moment with spatially fluctuating amplitude.Comment: 4pages, 5 figues, submitted to J. Phys. Soc. Jp

Magnetization Process of Kagome-Lattice Heisenberg Antiferromagnet

The magnetization process of the isotropic Heisenberg antiferromagnet on the kagome lattice is studied. Data obtained from the numerical-diagonalization method are reexamined from the viewpoint of the derivative of the magnetization with respect to the magnetic field. We find that the behavior of the derivative at approximately one-third of the height of the magnetization saturation is markedly different from that for the cases of typical magnetization plateaux. The magnetization process of the kagome-lattice antiferromagnet reveals a new phenomenon, which we call the "magnetization ramp".Comment: 4 pages, 5figures, accepted in J. Phys. Soc. Jpn

Universal emergence of the one-third plateau in the magnetization process of frustrated quantum spin chains

We present a numerical study of the magnetization process of frustrated quantum spin-S chains with S=1, 3/2, 2 as well as the classical limit. Using the exact diagonalization and density-matrix renormalization techniques, we provide evidence that a plateau at one third of the saturation magnetization exists in the magnetization curve of frustrated spin-S chains with S>1/2. Similar to the case of S=1/2, this plateau state breaks the translational symmetry of the Hamiltonian and realizes an up-up-down pattern in the spin component parallel to the external field. Our study further shows that this plateau exists both in the cases of an isotropic exchange and in the easy-axis regime for spin-S=1, 3/2, and 2, but is absent in classical frustrated spin chains with isotropic interactions. We discuss the magnetic phase diagram of frustrated spin-1 and spin-3/2 chains as well as other emergent features of the magnetization process such as kink singularities, jumps, and even-odd effects. A quantitative comparison of the one-third plateau in the easy-axis regime between spin-1 and spin-3/2 chains on the one hand and the classical frustrated chain on the other hand indicates that the critical frustration and the phase boundaries of this state rapidly approach the classical result as the spin S increases.Comment: 15 pages RevTex4, 13 figure

Thermodynamic properties of a tetramer ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain as a model system for Cu(3-Clpy)2_2(N3_3)2_2

Thermodynamic properties of a tetramer ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain are investigated by the use of an exact mapping transformation technique. Exact results for the magnetization, susceptibility and specific heat in the zero as well as nonzero magnetic field are presented and discussed in detail. The results obtained from the mapping are compared with the relevant experimental data of Cu(3-Clpy)$_2$(N$_3$)$_2$ (3-Clpy=3-Chloropyridine).Comment: 10 pages, 1 table, 14 figures, to be presented at CSMAG04 conferenc

Magnetization Plateaus in a Solvable 3-Leg Spin Ladder

We present a solvable ladder model which displays magnetization plateaus at fractional values of the total magnetization. Plateau signatures are also shown to exist along special lines. The model has isotropic Heisenberg interactions with additional many-body terms. The phase diagram can be calculated exactly for all values of the rung coupling and the magnetic field. We also derive the anomalous behaviour of the susceptibility near the plateau boundaries. There is good agreement with the phase diagram obtained recently for the pure Heisenberg ladders by numerical and perturbative techniques.Comment: 4 pages, revtex, 3 postscript figures, small changes to the text and references update

Magnetization process for a quasi-one-dimensional S=1 antiferromagnet

We investigate the magnetization process for a quasi-one-dimensional S=1 antiferromagnet with bond alternation. By combining the density matrix renormalization group method with the interchain mean-field theory, we discuss how the interchain coupling affects the magnetization curve. It is found that the width of the magnetization plateau is considerably reduced upon introducing the interchain coupling. We obtain the phase diagram in a magnetic field. The effect of single-ion anisotropy is also addressed.Comment: 6 pages, 7 eps figure

A Strong-Coupling Approach to the Magnetization Process of Polymerized Quantum Spin Chains

Polymerized quantum spin chains (i.e. spin chains with a periodic modulation of the coupling constants) exhibit plateaux in their magnetization curves when subjected to homogeneous external magnetic fields. We argue that the strong-coupling limit yields a simple but general explanation for the appearance of plateaux as well as of the associated quantization condition on the magnetization. We then proceed to explicitly compute series for the plateau boundaries of trimerized and quadrumerized spin-1/2 chains. The picture is completed by a discussion how the universality classes associated to the transitions at the boundaries of magnetization plateaux arise in many cases from a first order strong-coupling effective Hamiltonian.Comment: 5 pages REVTeX, three PostScript figures included using psfig.st

Product Wave Function Renormalization Group: construction from the matrix product point of view

We present a construction of a matrix product state (MPS) that approximates the largest-eigenvalue eigenvector of a transfer matrix T, for the purpose of rapidly performing the infinite system density matrix renormalization group (DMRG) method applied to two-dimensional classical lattice models. We use the fact that the largest-eigenvalue eigenvector of T can be approximated by a state vector created from the upper or lower half of a finite size cluster. Decomposition of the obtained state vector into the MPS gives a way of extending the MPS, at the system size increment process in the infinite system DMRG algorithm. As a result, we successfully give the physical interpretation of the product wave function renormalization group (PWFRG) method, and obtain its appropriate initial condition.Comment: 8 pages, 8 figure

Experimental Verification of the Gapless Point in the SS=1 Antiferromagnetic Bond Alternating Chain

Susceptibility and high field magnetization measurements have been performed on powder samples of an $S$=1 bond alternating chain compound [\{Ni(333-tet)($\mu$-N$_3$)\}$_n$](ClO$_4$)$_n$ (333-tet=tetraamine N,N'-bis(3-aminopropyl)-1,3-propanediamine). As the temperature is decreased, the susceptibility exhibits a round maximum at around 120 K and decreases gradually down to 10 K, and then falls down rapidly with a logarithmic curvature which is behavior of the susceptibility of a gapless or a nearly gapless antiferromagnetic chain. Magnetization up to 50 T at 1.4 K shows no or a very small gap in this compound. We have carried out numerical calculations for the $S$=1 antiferromagnetic bond alternating chain with various alternating ratios $\alpha$ and obtained a very good agreement between experiments and calculations for $\alpha$=0.6. We verify experimentally that the gapless point exists around $\alpha$=0.6.Comment: 12 pages, 4 Postscript figures, uses REVTE

Propiedades ópticas de películas de dióxido de vanadio como recubrimiento termocrómico en ventanas

The optical properties of vanadium dioxide (VO2) thin film have been studied for the potential application of intelligent windows. The results show that VO2 film deposited on sapphire substrates exhibits good thermochromic effects, its IR transmittance changes 60% before and after phase transition, and has less thickness dependence than UV transmittance. Doping can significantly reduce transition temperature, such as to 30°C for 1.5% Mo doped VO2.Se han investigado las propiedades ópticas del dióxido de vanadio (VO2) aplicado como películas delgadas para posibles aplicaciones en ventanas inteligentes. Cuando el VO2 se deposita sobre sustratos de zafiro da lugar a efectos termocrómicos considerables; así, su transmitancia en el infrarrojo cambia en un 60 % después de la transición de fase del dióxido de vanadio, teniendo una dependencia menor con el espesor que la transmitancia en el ultravioleta. El efecto de aditivos sobre estas películas de dioxido de vanadio da lugar a una disminución de la temperatura de dicha transición responsable del efecto termocrómico, de manera que se produce a 30°C con el 1,5 % de adición de Mo