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Register a new userLarge magnetic heat transport in a Haldane chain material Ni(C$_3H_{10}N_2)_2NO_2ClO_4
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We report a study on the heat transport of an S = 1 Haldane chain compound Ni(C_3H_{10}N_2)_2NO_2ClO_4 at low temperatures and in magnetic fields. The zero-field thermal conductivities show a remarkable anisotropy for the heat current along the spin-chain direction (kappa_b) and the vertical direction (kappa_c), implying a magnetic contribution to the heat transport along the spin-chain direction. The magnetic-field-induced change of the spin spectrum has obviously opposite impacts on kappa_b and kappa_c. In particular, kappa_b(H) and kappa_c(H) curves show peak-like increases and dip-like decreases, respectively, at sim 9 T, which is the critical field that minimizes the spin gap. These results indicate a large magnetic thermal transport in this material.
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The bulk single crystals of $S = 1$ chain compound Ni(C$_3$H$_{10}$N$_2$)$_2$NO$_2$ClO$_4$ are grown by using a slow evaporation method at a constant temperature and a slow cooling method. It is found that the optimum condition of growing large crystals is via slow evaporation at 25 $^circ$C using 0.015 mol Ni(ClO$_4$)$_2$$cdot$6H$_2$O, 0.015 mol NaNO$_2$, and 0.03 mol 1,3-propanediamine liquid dissolved into 30 ml aqueous solvent. High-quality crystals with size up to $18 times 7.5 times 5$ mm$^3$ are obtained. The single crystals are characterized by measurements of x-ray diffraction, magnetic susceptibility, specific heat and thermal conductivity. The susceptibilities along three crystallographic axes are found to exhibit broad peaks at $sim 55$ K, and then decrease abruptly to zero at lower temperatures, which is characteristic of a Haldane chain system. The specific heat and the thermal conductivity along the $c$ axis can be attributed to the simple phononic contribution and are analyzed using the Debye approximation.
We have determined the magnetic phase diagram of the quasi-one-dimensional $S=$ 1 Heisenberg antiferromagnet $Ni (C_5 H_{14} N_2)_2 N_3 (PF_6)$ by specific heat measurements to 150 mK in temperature and 32 T in magnetic field. When field is applied along the spin-chain direction, a new phase appears at $H_{c2}approx 14$ T. For the previously known phases of field-induced order, accurate determination is made of the power-law exponents of the ordering temperature near the zero-temperature critical field $H_c$, owing to the four-fold improvement of the minimum temperature over the previous work. The results are compared with the predictions based on the Bose-Einstein condensation of triplet excitations. Substituting deuterium for hydrogen is found to slightly reduce the interchain exchange.
We report a study of the low-temperature heat transport in the quasi-one-dimensional S = 1/2 alternating antiferromagnetic-ferromagnetic chain compound (CH_{3})_{2}NH_{2}CuCl_{3}. Both the temperature and magnetic-field dependencies of thermal conductivity are very complicated, pointing to the important role of spin excitations. It is found that magnetic excitations act mainly as the phonon scatterers in a broad temperature region from 0.3 to 30 K. In magnetic fields, the thermal conductivity show drastic changes, particularly at the field-induced transitions from the low-field N{e}el state to the spin-gapped state, the field-induced magnetic ordered state, and the spin polarized state. In high fields, the phonon conductivity is significantly enhanced because of the weakening of spin fluctuations.
Impurity effect is systematically studied in doped Haldane material Pb(Ni$_{1-x}$$M_x$)$_2$V$_2$O$_8$ ($M$ = Mn, Co, Cu, and Mg) by use of DC and AC susceptibility, and heat capacity measurements. The occurrence of three-dimensional ordered state is universally observed for all the impurities and the complete temperature -- concentration phase diagrams are obtained, which are qualitatively similar to that in other spin-gap materials. The unique feature is found in the drastic dependence of the transition temperatures on the species of the impurities. The consideration of effective Hamiltonian based on VBS model makes it clear that the ferromagnetic next-nearest-neighbor interaction and the antiferromagnetic nearest-neighbor interaction between impurity and edge spins play a key role in the unique feature.
Inelastic neutron scattering was used to probe edge states in a quantum spin liquid. The experiment was performed on finite length antiferromagnetic spin-1 chains in Y_2BaNi_{1-x}Mg_xO_5. At finite fields, there is a Zeeman resonance below the Haldane gap. The wave vector dependence of its intensity provides direct evidence for staggered magnetization at chain ends, which decays exponentially towards the bulk (xi = 8(1) at T=0.1K). Continuum contributions to the chain end spectrum indicate inter-chain-segment interactions. We also observe a finite size blue shift of the Haldane gap.
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