共查询到20条相似文献,搜索用时 15 毫秒
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MASAYUKI HAGIWARA 《Molecular physics》2013,111(9):1489-1495
Electron spin resonance (ESR) was used to study the ground state properties of two kinds of spin (S) one Heisenberg antiferromagnetic chain systems, namely a uniform chain system (HAUC), which is well known as the Haldane system, and a bond alternating chain system (HABA). To investigate and compare the features of the ground state, two nickel chain compounds doped with non-magnetic Zn2+ impurities were studied. The HAUC was modelled with Ni(1,3-pn)2(μ-NO2)(ClO4)(1,3-pn = 1,3-propanediamine), abbreviated as NINO, while the HABA was modelled with Ni(333-tet)(μ-NO2)(ClO4) (333-tet = bis-(3-aminopropyl)-1,3-propanediamine), abbreviated as NTENP. Both systems have a singlet ground state with an excitation gap. The ground state of NINO approximates well to the valence bond solid state, thus producing S = 1/2 spins at the sites neighbouring the impurities. The angular dependence of the ESR signals of NINO:Zn is explained by the anisotropy of the g tensor for spin 1/2. On the other hand, the ground state of NTENP is expected to be in the singlet dimer phase based on the ratio of alternating bond strengths. In this case, it is expected that the S = 1 spins will appear at the sites neighbouring the impurities without forming the singlet dimer. From ESR studies of NTENP:Zn was observed the triplet state (S = 1), induced by the impurity doping, which is consistent with the above picture. 相似文献
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《Physics letters. A》1997,235(5):545-550
In order to confirm the picture of domain-wall excitations in the hidden antiferromagnetic order of the Haldane phase, the structure of the low-lying excitations in the S = 1 antiferromagnetic Heisenberg chain is studied by a quantum Monte Carlo method. It is confirmed that there exists a finite energy gap between the first- and the second-excited states at k = π as well as between the ground state and the first-excited state at k = π. In the thermodynamic limit, the second-excited state at k = π is separated from the ground state by the gap which is three times as large as the Haldane gap. From the size dependences of the low-lying-excitation energies, the interactions between the elementary excitations in the excited states are concluded to be repulsive. 相似文献
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de Vries MA Kamenev KV Kockelmann WA Sanchez-Benitez J Harrison A 《Physical review letters》2008,100(15):157205
We present a detailed analysis of the heat capacity of a near-perfect S=1/2 kagome antiferromagnet, zinc paratacamite Zn(x)Cu(4-x)(OH)(6)Cl(2), as a function of stoichiometry x-->1 and for fields of up to 9 T. We obtain the heat capacity intrinsic to the kagome layers by accounting for the weak Cu2+/Zn2+ exchange between the Cu and the Zn sites, which was measured independently for x=1 using neutron diffraction. The evolution of the heat capacity for x=0.8...1 is then related to the hysteresis in the magnetic susceptibility. We conclude that for x>0.8 zinc paratacamite is a spin liquid without a spin gap, in which unpaired spins give rise to a macroscopically degenerate ground state manifold with increasingly glassy dynamics as x is lowered. 相似文献
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We have performed electron spin resonance measurements over a wide frequency and magnetic field range on a single crystal of the S=1 quasi-one-dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6). We observed gapped excitation branches above the critical field H(c) where the Haldane gap closes. These branches are analyzed by a phenomenological field theory using the complex-field phi(4) model. A satisfactory agreement between experiment and theory is obtained. 相似文献
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G. M. Rocha-Filho A. S.T. Pires M. E. Gouvêa 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):7-14
We study the one-dimensional isotropic spin-1 Heisenberg
magnet with antiferromagnetic nearest-neighbor (nn) and
next-nearest-neighbor (nnn) interactions by using the modified spin
wave theory (MSWT). The ground state energy and the singlet-triplet
energy gap are obtained for several values of j, defined as the
ratio of the nnn interaction constant to the nn one. We also compare
two different ways of implementing the MSWT currently found in the
literature, and show that, despite the remarkable differences between
the equations to be solved in each procedure, the results given by
both are equivalent, except for the predicted value of the
jmax, the maximum value of j accessible in each treatment.
Here, we suggest that jmax is related to the disorder point of
the first kind. Our results show that the ground state and the gap
energies increase with j, for j ≤jmax, in accordance to
previous numerical results. 相似文献
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Jan Koláček 《Czechoslovak Journal of Physics》1990,40(3):345-352
The statistical approach is adopted in an attempt to find the antiferromagnetic ground state. As a result an eigenstate of the Heisenberg hamiltonian is found which is not the true ground state, but which could serve as a useful starting point for other methods.The author is grateful to ing. P. Novák for valuable discussions. 相似文献
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S. V. Demishev A. V. Semeno H. Ohta S. Okubo I. E. Tarasenko T. V. Ishchenko N. E. Sluchanko 《JETP Letters》2006,84(5):249-253
Anomalous polarization characteristics of magnetic resonance in CuGeO3 doped with 2% Co impurity are reported. For the Faraday geometry, this mode is damped for the microwave field B
ω aligned along a certain crystallographic direction, showing that the character of magnetic oscillation differs from the standard
spin precession. The observed resonance coexists with the ESR on Cu2+ chains; it is argued not to be caused by “impurity” EPR, as previously claimed, but to correspond to a previously unknown
collective mode of magnetic oscillations in an S = 1/2 AF quantum spin chain.
The text was submitted by the authors in English. 相似文献
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A recent proposal by Duke and Ford (Surface Sci. 111 (1981) L685) of strong correlations at the metastable (1× 1) Si(111) surface is shown to be equivalent to our earlier theory of magnetic or charge instabilities at this surface. It is recalled how this can be discussed from a perturbation analysis. Estimates of the Coulomb parameter U are given using recent theoretical results for dangling bond states in silicon. They support the conclusion of an antiferromagnetic 2 × 1 ground state for this surface. 相似文献
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