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Observations of spin gaps in the S=1/2 quasi-one-dimensional magnet A10Cu17O29 (A=Sr, Ca, Y, Bi)
Abstract
Magnetic susceptibility and electron spin resonance measurements have
been performed on the S=1/2 quasi-one-dimensional compound
A10Cu17O29 (A=Sr, Ca, Y, Bi), in which
copper ions are located in the isolated chains of the Cu-O squares and
the two-leg ladder planes. The magnetic excitations in the copper chains
are suggested to be the Wannier spin excitations. The spin gaps have
shown to exist for both spin chains and two-leg spin ladders.
... The high-temperature superconductivity at 80 K and at ambient pressure was reported several years ago in the spin-ladder crystals [1] and was confirmed in further studies234. These layered incommensurate crystals can be described by the formula (A 2 Cu2 O3 )m (CuO 2 )n , where A represents Sr and Ca mainly, a small amount of Bi and sometimes other impurities like Al, Pb, and Y. ...
... The high-temperature superconductivity at 80 K and at ambient pressure was reported several years ago in the spin-ladder crystals [1] and was confirmed in further studies [2][3][4]. These layered incommensurate crystals can be described by the formula (A 2 Cu2 O3 )m (CuO 2 )n , where A represents Sr and Ca mainly, a small amount of Bi and sometimes other impurities like Al, Pb, and Y. ...
Transmission electron microscopy and X-ray diffraction proved chain/ ladder incommensurate single crystal structure of investigated samples. The incommensurate ratio was determined from the X-ray and electron diffraction being equal to 0.704. Diffuse scattering intensities localised on the planes perpendicular to the c*-axis and passing through the spots originating from the periodicity of chain sublattice were detected. High-angle grain boundary or twinning formed by rotation of 33.3° around [100] direction was observed. High-resolution electron microscopy images revealed the stacking faults in ac planes.
... The temperature dependence of magnetic susceptibility 1(T) was investigated on a series of copper oxysalt minerals with various Cu-containing units. The samples studied were The temperature dependence of magnetic susceptibility in minerals was analyzed using an S = 1/2 isolated antiferromagnetic dimer model (Carlin, 1986), which has been used (Baran et al., 1999) for other Cu-containing compounds. In the analysis of the experimental results, the contributions of the free magnetic ions and other possible imperfections were also taken into account as the Curie±Weiss-like term. ...
The structure of copper oxysalt minerals is analyzed on the basis of the classification scheme developed earlier for synthetic cuprates. The copper-oxygen compounds were considered as the salts of hypothetical copper acids with characteristic Cu-containing structural units of various dimensions formed by a polymerization of the CuO squares. The results of magnetic susceptibility measurements performed recently were analyzed from the viewpoint of the developed extended structural classification scheme. The dimerization of magnetic moments was considered as a property of cuprates which was strongly dependent on the type of Cu-containing structural unit. A further extension of the structural classification scheme for cuprates is also discussed.
Magnetization M(T) and M(H) data of single crystals of the 5 = 1/2 quasi-one-dimensional system (A2Cu2O3)m(CuO2) n with various A-site constituents are compared. The studied orthorhombic, incommensurate crystals are characterized by m/n = 5/7, 7/10, and 9/13. The role of rare-earth ions located in A-sites is discussed.
We discuss an electronic model consisting of two chains or planes, each described by a t-J model, coupled by t'-J' interactions between them. For J'~J or larger we show the presence of a spin-gap and hole-pair formation upon doping. The model exhibits superconducting pairing correlations away from half filling. We support our claims by numerical studies of the spin gap, the binding energy of holes, and the pairing correlations on finite clusters. The hole-pairing operator is a spin singlet with one member of the pair in each chain or plane. Our model belongs to the universality class of the U>t. We argue that this model may be physically realized by doping the orthorhombic compound (VO)2P2O7.
We have investigated spin dynamics of both the ladder and the chain sites in Sr 14 Cu 24 O 41 by Cu-NMR and Cu-NQR. From the NMR shift, K spin , and nuclear spin-lattice relaxation time, T 1 , the energy gaps in the spin excitation spectrum are confirmed to be Δ=140 K for the chain site and Δ=470 K for the ladder site for Sr 14 Cu 24 O 41 . Doping effects on the spin gaps and electric field gradient at the Cu sites were also investigated by the substituting of Ca, Y and La for Sr. The spin gap of the ladder site decreases with increasing x for Sr 14- x Ca x Cu 24 O 41 and seems to collapse at around x =13 for Ca substitution.
The single crystal habit and structure of new incommensurate-type phases
in the system [A 2Cu 2O 3]
m[CuO 2] n (where A is alkaline earth
and trivalent metals) were analyzed. Needle- and platelet-like crystals
were grown from the melt by slow-cooling or decantation. Three
modifications of the phases with m/n values equal to {5}/{7}, {7}/{10}
and {9}/{13} were distinguished. The distortion of the second structural
fragment, the plane of Cu-O ribbons, was determined to be significantly
larger than for the first fragment composed of a ladder between two
A-cation layers. Superconducting crystals ( Tc=80-85 K) were
attributed to the modification with m=5 and n=7.
We review systematic NMR studies on underdoped high-Tc cuprates and two-leg spin-ladder systems, focusing on their spin gap and dynamics. The pressure-induced superconductivity was discovered in Sr14− xCa xCu24O41 comprising the quasi-one-dimensional S = ½ two-leg spin-ladder Cu2O3 planes. Remarkably, the new parent cuprate is the Mott insulator with the spin gap in contrast to the antiferromagnetic (AF) insulator for the high-Tc cuprates. From the Cu-NMR results in the ladder Cu2O3 plane on single crystals Sr14− xCa xCu24O41 with x = 9 (hereafter denoted as Ca9) and x = 11.5 (Ca11.5), it is shown that the spin gap, Δ = 510K in the Sr14 is significantly reduced upon isovalent Ca substitution, but its magnitude remains nearly constant with Δ = 270 and 280K for the Ca9 and Ca11.5, respectively. In T range of T ⩾ Δ, the spin dynamics in carrier-doped two-leg spin-ladder systems are characterized by the behaviour similar to the S = ½ 1D Heisenberg system. By contrast, the transport property shares a common feature, i.e, due to the spin-gap opening the charge transport is confined in the 2D CuO2 plane for underdoped high-Tc, cuprates and in the quasi-1 D ladder for spin-ladder compounds.
We have performed magnetic susceptibility and electron spin resonance measurements on the quasi-one-dimensional magnet Sr14Cu24O41, which has simple chains and two-leg ladder chains of copper ions. The magnetic signals which we observed below room temperature mainly come from the simple chains. The experimental results show that the simple chain unexpectedly has a spin gap in the excitation spectrum, which originates from a dimerized state. © 1996 The American Physical Society.